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[PATCH 2/8] Pass all scan keys to BRIN consistent function at once 36+ messages / 15 participants [nested] [flat]
* [PATCH 2/8] Pass all scan keys to BRIN consistent function at once @ 2020-09-12 13:07 Tomas Vondra <[email protected]> 0 siblings, 0 replies; 36+ messages in thread From: Tomas Vondra @ 2020-09-12 13:07 UTC (permalink / raw) Passing all scan keys to the BRIN consistent function at once may allow elimination of additional ranges, which would be impossible when only passing individual scan keys. The code continues to support both the original (one scan key at a time) and new (all scan keys at once) approaches, depending on whether the consistent function accepts three or four arguments. Author: Tomas Vondra <[email protected]> Reviewed-by: Alvaro Herrera <[email protected]> Reviewed-by: Mark Dilger <[email protected]> Reviewed-by: Alexander Korotkov <[email protected]> Discussion: https://postgr.es/m/[email protected] --- src/backend/access/brin/brin.c | 158 +++++++++++++++++++----- src/backend/access/brin/brin_validate.c | 4 +- 2 files changed, 126 insertions(+), 36 deletions(-) diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c index 27ba596c6e..f9a0476024 100644 --- a/src/backend/access/brin/brin.c +++ b/src/backend/access/brin/brin.c @@ -390,6 +390,9 @@ bringetbitmap(IndexScanDesc scan, TIDBitmap *tbm) BrinMemTuple *dtup; BrinTuple *btup = NULL; Size btupsz = 0; + ScanKey **keys; + int *nkeys; + int keyno; opaque = (BrinOpaque *) scan->opaque; bdesc = opaque->bo_bdesc; @@ -411,6 +414,66 @@ bringetbitmap(IndexScanDesc scan, TIDBitmap *tbm) */ consistentFn = palloc0(sizeof(FmgrInfo) * bdesc->bd_tupdesc->natts); + /* + * Make room for per-attribute lists of scan keys that we'll pass to the + * consistent support procedure. We allocate space for all attributes, so + * that we don't have to bother determining which attributes are used. + * + * XXX The widest table can have ~1600 attributes, so this may allocate a + * couple kilobytes of memory). We could invent a more compact approach + * (with just space for used attributes) but that would make the matching + * more complicated, so it may not be a win. + */ + keys = palloc0(sizeof(ScanKey *) * bdesc->bd_tupdesc->natts); + nkeys = palloc0(sizeof(int) * bdesc->bd_tupdesc->natts); + + /* + * Preprocess the scan keys - split them into per-attribute arrays. + */ + for (keyno = 0; keyno < scan->numberOfKeys; keyno++) + { + ScanKey key = &scan->keyData[keyno]; + AttrNumber keyattno = key->sk_attno; + + /* + * The collation of the scan key must match the collation used in the + * index column (but only if the search is not IS NULL/ IS NOT NULL). + * Otherwise we shouldn't be using this index ... + */ + Assert((key->sk_flags & SK_ISNULL) || + (key->sk_collation == + TupleDescAttr(bdesc->bd_tupdesc, + keyattno - 1)->attcollation)); + + /* First time we see this index attribute, so init as needed. */ + if (!keys[keyattno - 1]) + { + FmgrInfo *tmp; + + /* + * This is a bit of an overkill - we don't know how many scan keys + * are there for this attribute, so we simply allocate the largest + * number possible. This may waste a bit of memory, but we only + * expect small number of scan keys in general, so this should be + * negligible, and it's cheaper than having to repalloc + * repeatedly. + */ + keys[keyattno - 1] = palloc0(sizeof(ScanKey) * scan->numberOfKeys); + + /* First time this column, so look up consistent function */ + Assert(consistentFn[keyattno - 1].fn_oid == InvalidOid); + + tmp = index_getprocinfo(idxRel, keyattno, + BRIN_PROCNUM_CONSISTENT); + fmgr_info_copy(&consistentFn[keyattno - 1], tmp, + CurrentMemoryContext); + } + + /* Add key to the per-attribute array. */ + keys[keyattno - 1][nkeys[keyattno - 1]] = key; + nkeys[keyattno - 1]++; + } + /* allocate an initial in-memory tuple, out of the per-range memcxt */ dtup = brin_new_memtuple(bdesc); @@ -471,7 +534,7 @@ bringetbitmap(IndexScanDesc scan, TIDBitmap *tbm) } else { - int keyno; + int attno; /* * Compare scan keys with summary values stored for the range. @@ -481,51 +544,78 @@ bringetbitmap(IndexScanDesc scan, TIDBitmap *tbm) * no keys. */ addrange = true; - for (keyno = 0; keyno < scan->numberOfKeys; keyno++) + for (attno = 1; attno <= bdesc->bd_tupdesc->natts; attno++) { - ScanKey key = &scan->keyData[keyno]; - AttrNumber keyattno = key->sk_attno; - BrinValues *bval = &dtup->bt_columns[keyattno - 1]; + BrinValues *bval; Datum add; - /* - * The collation of the scan key must match the collation - * used in the index column (but only if the search is not - * IS NULL/ IS NOT NULL). Otherwise we shouldn't be using - * this index ... - */ - Assert((key->sk_flags & SK_ISNULL) || - (key->sk_collation == - TupleDescAttr(bdesc->bd_tupdesc, - keyattno - 1)->attcollation)); + /* skip attributes without any scan keys */ + if (nkeys[attno - 1] == 0) + continue; - /* First time this column? look up consistent function */ - if (consistentFn[keyattno - 1].fn_oid == InvalidOid) - { - FmgrInfo *tmp; + bval = &dtup->bt_columns[attno - 1]; - tmp = index_getprocinfo(idxRel, keyattno, - BRIN_PROCNUM_CONSISTENT); - fmgr_info_copy(&consistentFn[keyattno - 1], tmp, - CurrentMemoryContext); - } + Assert((nkeys[attno - 1] > 0) && + (nkeys[attno - 1] <= scan->numberOfKeys)); /* * Check whether the scan key is consistent with the page * range values; if so, have the pages in the range added * to the output bitmap. * - * When there are multiple scan keys, failure to meet the - * criteria for a single one of them is enough to discard - * the range as a whole, so break out of the loop as soon - * as a false return value is obtained. + * The opclass may or may not support processing of + * multiple scan keys. We can determine that based on the + * number of arguments - functions with extra parameter + * (number of scan keys) do support this, otherwise we + * have to simply pass the scan keys one by one, as + * before. */ - add = FunctionCall3Coll(&consistentFn[keyattno - 1], - key->sk_collation, - PointerGetDatum(bdesc), - PointerGetDatum(bval), - PointerGetDatum(key)); - addrange = DatumGetBool(add); + if (consistentFn[attno - 1].fn_nargs >= 4) + { + Oid collation; + + /* + * Collation from the first key (has to be the same + * for all keys for the same attribue). + */ + collation = keys[attno - 1][0]->sk_collation; + + /* Check all keys at once */ + add = FunctionCall4Coll(&consistentFn[attno - 1], + collation, + PointerGetDatum(bdesc), + PointerGetDatum(bval), + PointerGetDatum(keys[attno - 1]), + Int32GetDatum(nkeys[attno - 1])); + addrange = DatumGetBool(add); + } + else + { + /* + * Check keys one by one + * + * When there are multiple scan keys, failure to meet + * the criteria for a single one of them is enough to + * discard the range as a whole, so break out of the + * loop as soon as a false return value is obtained. + */ + int keyno; + + for (keyno = 0; keyno < nkeys[attno - 1]; keyno++) + { + add = FunctionCall3Coll(&consistentFn[attno - 1], + keys[attno - 1][keyno]->sk_collation, + PointerGetDatum(bdesc), + PointerGetDatum(bval), + PointerGetDatum(keys[attno - 1][keyno])); + addrange = DatumGetBool(add); + + /* mismatching key, no need to look further */ + if (!addrange) + break; + } + } + if (!addrange) break; } diff --git a/src/backend/access/brin/brin_validate.c b/src/backend/access/brin/brin_validate.c index 6d4253c05e..11835d85cd 100644 --- a/src/backend/access/brin/brin_validate.c +++ b/src/backend/access/brin/brin_validate.c @@ -97,8 +97,8 @@ brinvalidate(Oid opclassoid) break; case BRIN_PROCNUM_CONSISTENT: ok = check_amproc_signature(procform->amproc, BOOLOID, true, - 3, 3, INTERNALOID, INTERNALOID, - INTERNALOID); + 3, 4, INTERNALOID, INTERNALOID, + INTERNALOID, INT4OID); break; case BRIN_PROCNUM_UNION: ok = check_amproc_signature(procform->amproc, BOOLOID, true, -- 2.26.2 --------------82D677E9F94AC7574E460205 Content-Type: text/x-patch; charset=UTF-8; name="0003-Process-all-scan-keys-in-existing-BRIN-opcl-20210308.patch" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename*0="0003-Process-all-scan-keys-in-existing-BRIN-opcl-20210308.pa"; filename*1="tch" ^ permalink raw reply [nested|flat] 36+ messages in thread
* Built-in Raft replication @ 2025-04-14 17:15 Konstantin Osipov <[email protected]> 0 siblings, 3 replies; 36+ messages in thread From: Konstantin Osipov @ 2025-04-14 17:15 UTC (permalink / raw) To: [email protected] Hi, I am considering starting work on implementing a built-in Raft replication for PostgreSQL. Raft's advantage is that it unifies log replication, cluster configuration/membership/topology management and initial state transfer into a single protocol. Currently the cluster configuration/topology is often managed by Patroni, or similar tools, however, it seems there are certain usability drawbacks with this approach: - it's a separate tool, requiring an external state provider like etcd; raft could store its configuration in system tables; this is also an observability improvement since everyone could look up cluster state the same way as everything else - same for watchdog; raft has a built-in failure detector that's configuration aware; - flexible quorums; currently quorum size is a configurable; with a built-in raft, extending the quorum could be a matter of starting a new node and pointing it to an existing cluster Going forward I can see PostgreSQL providing transparent bouncing on pg_wire level, given that Raft state is now part of the system, so drivers and all cluster nodes could easily see where the leader is. If anyone is working on Raft already I'd be happy to discuss the details. I am fairly new to the PostgreSQL hackers ecosystem so cautious of starting work in isolation/knowing there is no interest in accepting the feature into the trunk. Thanks, -- Konstantin Osipov ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-14 17:44 Kirill Reshke <[email protected]> parent: Konstantin Osipov <[email protected]> 2 siblings, 2 replies; 36+ messages in thread From: Kirill Reshke @ 2025-04-14 17:44 UTC (permalink / raw) To: Konstantin Osipov <[email protected]>; +Cc: [email protected] On Mon, 14 Apr 2025 at 22:15, Konstantin Osipov <[email protected]> wrote: > > Hi, Hi > I am considering starting work on implementing a built-in Raft > replication for PostgreSQL. > Just some thought on top of my mind, if you need my voice here: I have a hard time believing the community will be positive about this change in-core. It has more changes as contrib extension. In fact, if we want a built-in consensus algorithm, Paxos is a better option, because you can use postgresql as local crash-safe storage for single decree paxos, just store your state (ballot number, last voice) in a heap table. OTOH Raft needs to write its own log, and what's worse, it sometimes needs to remove already written parts of it (so, it is not appended only, unlike WAL). If you have a production system which maintains two kinds of logs with different semantics, it is a very hard system to maintain.. There is actually a prod-ready (non open source) implementation of RAFT as extension, called BiHA, by pgpro. Just some thought on top of my mind, if you need my voice here. -- Best regards, Kirill Reshke ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-14 19:00 Konstantin Osipov <[email protected]> parent: Kirill Reshke <[email protected]> 1 sibling, 0 replies; 36+ messages in thread From: Konstantin Osipov @ 2025-04-14 19:00 UTC (permalink / raw) To: Kirill Reshke <[email protected]>; +Cc: [email protected] * Kirill Reshke <[email protected]> [25/04/14 20:48]: > > I am considering starting work on implementing a built-in Raft > > replication for PostgreSQL. > > > > Just some thought on top of my mind, if you need my voice here: > > I have a hard time believing the community will be positive about this > change in-core. It has more changes as contrib extension. In fact, if > we want a built-in consensus algorithm, Paxos is a better option, > because you can use postgresql as local crash-safe storage for single > decree paxos, just store your state (ballot number, last voice) in a > heap table. But Raft is a log replication algorithm, not a consensus algorithm. It does use consensus, but that's for leader election. Paxos could be used for log replication, but that would be expensive. In fact etcd uses Raft, and etcd is used by Patroni. So I completely lost your line of thought here. > OTOH Raft needs to write its own log, and what's worse, it sometimes > needs to remove already written parts of it (so, it is not appended > only, unlike WAL). If you have a production system which maintains two > kinds of logs with different semantics, it is a very hard system to > maintain.. My proposal is exactly to replace (or rather, extend) the current synchronous log replication with Raft. Entry removal is possible to stack on top of append-only format, and production implementations exist which do that. So, no, it's a single log, and in fact the current WAL will do. > There is actually a prod-ready (non open source) implementation of > RAFT as extension, called BiHA, by pgpro. My guess biha is an extension since a proprietary code is easier to maintain that way. I'd rather say the fact that there is a proprietary implementation out in the field confirms it could be a good idea to have it in PostgreSQL trunk. In any case I'm interested in contributing to the trunk, not building a proprietary module/fork. -- Konstantin Osipov ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-15 10:20 Aleksander Alekseev <[email protected]> parent: Konstantin Osipov <[email protected]> 2 siblings, 3 replies; 36+ messages in thread From: Aleksander Alekseev @ 2025-04-15 10:20 UTC (permalink / raw) To: Konstantin Osipov <[email protected]>; +Cc: [email protected] Hi Konstantin, > I am considering starting work on implementing a built-in Raft > replication for PostgreSQL. Generally speaking I like the idea. The more important question IMO is whether we want to maintain Raft within the PostgreSQL core project. Building distributed systems on commodity hardware was a popular idea back in the 2000s. These days you can rent a server with 2 Tb of RAM for something like 2000 USD/month (numbers from my memory that were valid ~5 years ago) which will fit many of the existing businesses (!) in memory. And you can rent another one for a replica, just in order not to recover from a backup if something happens to your primary server. The common wisdom is if you can avoid building distributed systems, don't build one. Which brings the question if we want to maintain something like this (which will include logic for cases when a node joins or leaves the cluster, proxy server / service discovery for clients, test cases / infrastructure for all this and also upgrading the cluster, docs, ...) for a presumably view users which business doesn't fit in a single server *and* they want an automatic failover (not the manual one) *and* they don't use Patroni/Stolon/CockroachDB/Neon/... already. Although the idea is tempting personally I'm inclined to think that it's better to invest community resources into something else. -- Best regards, Aleksander Alekseev ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-15 11:14 Konstantin Osipov <[email protected]> parent: Kirill Reshke <[email protected]> 1 sibling, 0 replies; 36+ messages in thread From: Konstantin Osipov @ 2025-04-15 11:14 UTC (permalink / raw) To: Yura Sokolov <[email protected]>; +Cc: Kirill Reshke <[email protected]>; [email protected] * Yura Sokolov <[email protected]> [25/04/15 12:02]: > > OTOH Raft needs to write its own log, and what's worse, it sometimes > > needs to remove already written parts of it (so, it is not appended > > only, unlike WAL). If you have a production system which maintains two > > kinds of logs with different semantics, it is a very hard system to > > maintain.. > > Raft is log replication protocol which uses log position and term. > But... PostgreSQL already have log position and term in its WAL structure. > PostgreSQL's timeline is actually the Term. > Raft implementer needs just to correct rules for Term/Timeline switching: > - instead of "next TimeLine number is just increment of largest known > TimeLine number" it needs to be "next TimeLine number is the result of > Leader Election". > > And yes, "it sometimes needs to remove already written parts of it". > But... It is exactly what every PostgreSQL's cluster manager software have > to do to join previous leader as a follower to new leader - pg_rewind. > > So, PostgreSQL already have 70-90%% of Raft implementation details. > Raft doesn't have to be implemented in PostgreSQL. > Raft has to be finished!!! > > PS: One of the biggest issues is forced snapshot on replica promotion. It > really slows down leader switch time. It looks like it is not really > needed, or some small workaround should be enough. I'd say my pet peeve is storing the cluster topology (the so called raft configuration) inside the database, not in an external state provider. Agree on other points. -- Konstantin Osipov ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-15 11:15 Aleksander Alekseev <[email protected]> parent: Aleksander Alekseev <[email protected]> 2 siblings, 1 reply; 36+ messages in thread From: Aleksander Alekseev @ 2025-04-15 11:15 UTC (permalink / raw) To: [email protected]; +Cc: Yura Sokolov <[email protected]>; Konstantin Osipov <[email protected]> Hi Yura, > I've been working in a company which uses MongoDB (3.6 and up) as their > primary storage. And it seemed to me as "God Send". Everything just worked. > Replication was as reliable as one could imagine. It outlives several > hardware incidents without manual intervention. It allowed cluster > maintenance (software and hardware upgrades) without application downtime. > I really dream PostgreSQL will be as reliable as MongoDB without need of > external services. I completely understand. I had exactly the same experience with Stolon. Everything just worked. And the setup took like 5 minutes. It's a pity this project doesn't seem to get as much attention as Patroni. Probably because attention requires traveling and presenting the project at conferences which costs money. Or perhaps people are just happy with Patroni. I'm not sure in which state Stolon is today. -- Best regards, Aleksander Alekseev ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-15 11:20 Yura Sokolov <[email protected]> parent: Aleksander Alekseev <[email protected]> 0 siblings, 0 replies; 36+ messages in thread From: Yura Sokolov @ 2025-04-15 11:20 UTC (permalink / raw) To: Aleksander Alekseev <[email protected]>; [email protected]; +Cc: Konstantin Osipov <[email protected]> 15.04.2025 14:15, Aleksander Alekseev пишет: > Hi Yura, > >> I've been working in a company which uses MongoDB (3.6 and up) as their >> primary storage. And it seemed to me as "God Send". Everything just worked. >> Replication was as reliable as one could imagine. It outlives several >> hardware incidents without manual intervention. It allowed cluster >> maintenance (software and hardware upgrades) without application downtime. >> I really dream PostgreSQL will be as reliable as MongoDB without need of >> external services. > > I completely understand. I had exactly the same experience with > Stolon. Everything just worked. And the setup took like 5 minutes. > > It's a pity this project doesn't seem to get as much attention as > Patroni. Probably because attention requires traveling and presenting > the project at conferences which costs money. Or perhaps people are > just happy with Patroni. I'm not sure in which state Stolon is today. But the key point: if PostgreSQL will be improved a bit, there will be no need neither in Patroni, nor in Stolon. Isn't it great? -- regards Yura Sokolov aka funny-falcon ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-15 11:23 Konstantin Osipov <[email protected]> parent: Aleksander Alekseev <[email protected]> 2 siblings, 0 replies; 36+ messages in thread From: Konstantin Osipov @ 2025-04-15 11:23 UTC (permalink / raw) To: Aleksander Alekseev <[email protected]>; +Cc: [email protected] * Aleksander Alekseev <[email protected]> [25/04/15 13:20]: > > I am considering starting work on implementing a built-in Raft > > replication for PostgreSQL. > > Generally speaking I like the idea. The more important question IMO is > whether we want to maintain Raft within the PostgreSQL core project. > > Building distributed systems on commodity hardware was a popular idea > back in the 2000s. These days you can rent a server with 2 Tb of RAM > for something like 2000 USD/month (numbers from my memory that were > valid ~5 years ago) which will fit many of the existing businesses (!) > in memory. And you can rent another one for a replica, just in order > not to recover from a backup if something happens to your primary > server. The common wisdom is if you can avoid building distributed > systems, don't build one. > > Which brings the question if we want to maintain something like this > (which will include logic for cases when a node joins or leaves the > cluster, proxy server / service discovery for clients, test cases / > infrastructure for all this and also upgrading the cluster, docs, ...) > for a presumably view users which business doesn't fit in a single > server *and* they want an automatic failover (not the manual one) > *and* they don't use Patroni/Stolon/CockroachDB/Neon/... already. > > Although the idea is tempting personally I'm inclined to think that > it's better to invest community resources into something else. My personal take away from this as a community member would be seamless coordinator failover in Greenplum and all of its forks (CloudBerry, Greengage, synxdata, what not). I also imagine there is a number of PostgreSQL derivatives that could benefit from built-in transparent failover since it standardizes the solution space. -- Konstantin Osipov ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-15 11:24 Konstantin Osipov <[email protected]> parent: Aleksander Alekseev <[email protected]> 2 siblings, 0 replies; 36+ messages in thread From: Konstantin Osipov @ 2025-04-15 11:24 UTC (permalink / raw) To: Yura Sokolov <[email protected]>; +Cc: Aleksander Alekseev <[email protected]>; [email protected] * Yura Sokolov <[email protected]> [25/04/15 14:02]: > I've been working in a company which uses MongoDB (3.6 and up) as their > primary storage. And it seemed to me as "God Send". Everything just worked. > Replication was as reliable as one could imagine. It outlives several > hardware incidents without manual intervention. It allowed cluster > maintenance (software and hardware upgrades) without application downtime. > I really dream PostgreSQL will be as reliable as MongoDB without need of > external services. thanks for pointing out mongodb, so built-in raft would help ferretdb as well. -- Konstantin Osipov ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-15 15:07 Greg Sabino Mullane <[email protected]> parent: Konstantin Osipov <[email protected]> 2 siblings, 2 replies; 36+ messages in thread From: Greg Sabino Mullane @ 2025-04-15 15:07 UTC (permalink / raw) To: Konstantin Osipov <[email protected]>; +Cc: [email protected] On Mon, Apr 14, 2025 at 1:15 PM Konstantin Osipov <[email protected]> wrote: > If anyone is working on Raft already I'd be happy to discuss > the details. I am fairly new to the PostgreSQL hackers ecosystem > so cautious of starting work in isolation/knowing there is no > interest in accepting the feature into the trunk. > Putting aside the technical concerns about this specific idea, it's best to start by laying out a very detailed plan of what you would want to change, and what you see as the costs and benefits. It's also extremely helpful to think about developing this as an extension. If you get stuck due to extension limitations, propose additional hooks. If the hooks will not work, explain why. Getting this into core is going to be a long, multi-year effort, in which people are going to be pushing back the entire time, so prepare yourself for that. My immediate retort is going to be: why would we add this if there are existing tools that already do the job just fine? Postgres has lots of tasks that it is happy to let other programs/OS subsystems/extensions/etc. handle instead. Cheers, Greg -- Crunchy Data - https://www.crunchydata.com Enterprise Postgres Software Products & Tech Support ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-15 17:27 Konstantin Osipov <[email protected]> parent: Greg Sabino Mullane <[email protected]> 1 sibling, 0 replies; 36+ messages in thread From: Konstantin Osipov @ 2025-04-15 17:27 UTC (permalink / raw) To: Greg Sabino Mullane <[email protected]>; +Cc: [email protected] * Greg Sabino Mullane <[email protected]> [25/04/15 18:08]: > > If anyone is working on Raft already I'd be happy to discuss > > the details. I am fairly new to the PostgreSQL hackers ecosystem > > so cautious of starting work in isolation/knowing there is no > > interest in accepting the feature into the trunk. > > > > Putting aside the technical concerns about this specific idea, it's best to > start by laying out a very detailed plan of what you would want to change, > and what you see as the costs and benefits. It's also extremely helpful to > think about developing this as an extension. If you get stuck due to > extension limitations, propose additional hooks. If the hooks will not > work, explain why. > > Getting this into core is going to be a long, multi-year effort, in which > people are going to be pushing back the entire time, so prepare yourself > for that. My immediate retort is going to be: why would we add this if > there are existing tools that already do the job just fine? Postgres has > lots of tasks that it is happy to let other programs/OS > subsystems/extensions/etc. handle instead. I had hoped I explained why external state providers can not provide the same seamless UX as built-in ones. The key idea is to have a built-in configuration management, so that adding and removing replicas does not require changes in multiple disjoint parts of the installation (server configurations, proxies, clients). I understand and accept that it's a multi-year effort, but I do not accept the retort - my main point is that external tools are not a replacement, and I'd like to reach consensus on that. -- Konstantin Osipov, Moscow, Russia ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-15 22:27 Nikolay Samokhvalov <[email protected]> parent: Greg Sabino Mullane <[email protected]> 1 sibling, 2 replies; 36+ messages in thread From: Nikolay Samokhvalov @ 2025-04-15 22:27 UTC (permalink / raw) To: Greg Sabino Mullane <[email protected]>; +Cc: Konstantin Osipov <[email protected]>; [email protected] On Tue, Apr 15, 2025 at 8:08 AM Greg Sabino Mullane <[email protected]> wrote: > On Mon, Apr 14, 2025 at 1:15 PM Konstantin Osipov <[email protected]> > wrote: > >> If anyone is working on Raft already I'd be happy to discuss >> the details. I am fairly new to the PostgreSQL hackers ecosystem >> so cautious of starting work in isolation/knowing there is no >> interest in accepting the feature into the trunk. >> > > Putting aside the technical concerns about this specific idea, it's best > to start by laying out a very detailed plan of what you would want to > change, and what you see as the costs and benefits. It's also extremely > helpful to think about developing this as an extension. If you get stuck > due to extension limitations, propose additional hooks. If the hooks will > not work, explain why. > This is exactly what I wanted to write as well. The idea is great. At the same time, I think, consensus on many decisions will be extremely hard to reach, so this project has a high risk of being very long. Unless it's an extension, at least in the beginning. Nik ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 04:07 Andrey Borodin <[email protected]> parent: Nikolay Samokhvalov <[email protected]> 1 sibling, 2 replies; 36+ messages in thread From: Andrey Borodin @ 2025-04-16 04:07 UTC (permalink / raw) To: Tom Lane <[email protected]>; +Cc: Konstantin Osipov <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; [email protected] > On 16 Apr 2025, at 04:19, Tom Lane <[email protected]> wrote: > > feebly, and seems to have a bus factor of 1. Another example is the > Spencer regex engine; we thought we could depend on Tcl to be the > upstream for that, but for a decade or more they've acted as though > *we* are the upstream. I think it's what Konstantin is proposing. To have our own Raft implementation, without dependencies. IMO to better understand what is proposed we need some more description of proposed systems. How the new system will be configured? initdb and what than? How new node joins cluster? What is running pg_rewind when necessary? Some time ago Peter E proposed to be able to start replication atop of empty directory, so that initial sync would be more straightforward. And also Heikki proposed to remove archive race condition when choosing new timeline. I think this steps are gradual movement in the same direction. My view is what Konstantin wants is automatic replication topology management. For some reason this technology is called HA, DCS, Raft, Paxos and many other scary words. But basically it manages primary_conn_info of some nodes to provide some fault-tolerance properties. I'd start to design from here, not from Raft paper. Best regards, Andrey Borodin. ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 04:26 Tom Lane <[email protected]> parent: Andrey Borodin <[email protected]> 1 sibling, 2 replies; 36+ messages in thread From: Tom Lane @ 2025-04-16 04:26 UTC (permalink / raw) To: Andrey Borodin <[email protected]>; +Cc: Konstantin Osipov <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; [email protected] Andrey Borodin <[email protected]> writes: > I think it's what Konstantin is proposing. To have our own Raft implementation, without dependencies. Hmm, OK. I thought that the proposal involved relying on some existing code, but re-reading the thread that was said nowhere. Still, that moves it from a large project to a really large project :-( I continue to think that it'd be best to try to implement it as an extension, at least up till the point of finding show-stopping reasons why it cannot be that. regards, tom lane ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 04:33 Ashutosh Bapat <[email protected]> parent: Andrey Borodin <[email protected]> 1 sibling, 3 replies; 36+ messages in thread From: Ashutosh Bapat @ 2025-04-16 04:33 UTC (permalink / raw) To: Andrey Borodin <[email protected]>; +Cc: Tom Lane <[email protected]>; Konstantin Osipov <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; [email protected] On Wed, Apr 16, 2025 at 9:37 AM Andrey Borodin <[email protected]> wrote: > > My view is what Konstantin wants is automatic replication topology management. For some reason this technology is called HA, DCS, Raft, Paxos and many other scary words. But basically it manages primary_conn_info of some nodes to provide some fault-tolerance properties. I'd start to design from here, not from Raft paper. > In my experience, the load of managing hundreds of replicas which all participate in RAFT protocol becomes more than regular transaction load. So making every replica a RAFT participant will affect the ability to deploy hundreds of replica. We may build an extension which has a similar role in PostgreSQL world as zookeeper in Hadoop. It can be then used for other distributed systems as well - like shared nothing clusters based on FDW. There's already a proposal to bring CREATE SERVER to the world of logical replication - so I see these two worlds uniting in future. The way I imagine it is some PostgreSQL instances, which have this extension installed, will act as a RAFT cluster (similar to Zookeeper ensemble or etcd cluster). The distributed system based on logical replication or FDW or both will use this ensemble to manage its shared state. The same ensemble can be shared across multiple distributed clusters if it has scaling capabilities. -- Best Wishes, Ashutosh Bapat ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 05:24 Andrey Borodin <[email protected]> parent: Tom Lane <[email protected]> 1 sibling, 4 replies; 36+ messages in thread From: Andrey Borodin @ 2025-04-16 05:24 UTC (permalink / raw) To: Tom Lane <[email protected]>; +Cc: Konstantin Osipov <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; PostgreSQL Hackers <[email protected]> > On 16 Apr 2025, at 09:26, Tom Lane <[email protected]> wrote: > > Andrey Borodin <[email protected]> writes: >> I think it's what Konstantin is proposing. To have our own Raft implementation, without dependencies. > > Hmm, OK. I thought that the proposal involved relying on some existing > code, but re-reading the thread that was said nowhere. Still, that > moves it from a large project to a really large project :-( > > I continue to think that it'd be best to try to implement it as > an extension, at least up till the point of finding show-stopping > reasons why it cannot be that. I think I can provide some reasons why it cannot be neither extension, nor any part running within postmaster reign. 1. When joining cluster, there’s not PGDATA to run postmaster on top of it. 2. After failover, old Primary node must rejoin cluster by running pg_rewind and following timeline switch. The system in hand must be able to manipulate with PGDATA without starting Postgres. My question to Konstantin is Why wouldn’t you just add Raft to Patroni? Is there a reason why something like Patroni is not in core and noone rushes to get it in? Everyone is using it, or system like it. Best regards, Andrey Borodin. ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 05:39 Kirill Reshke <[email protected]> parent: Andrey Borodin <[email protected]> 3 siblings, 1 reply; 36+ messages in thread From: Kirill Reshke @ 2025-04-16 05:39 UTC (permalink / raw) To: Andrey Borodin <[email protected]>; +Cc: Tom Lane <[email protected]>; Konstantin Osipov <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; PostgreSQL Hackers <[email protected]> On Wed, 16 Apr 2025 at 10:25, Andrey Borodin <[email protected]> wrote: > > I think I can provide some reasons why it cannot be neither extension, nor any part running within postmaster reign. > > 1. When joining cluster, there’s not PGDATA to run postmaster on top of it. You can join the cluster on pg_basebackup of its master; So I dont get why this is an anti-extension restriction. > 2. After failover, old Primary node must rejoin cluster by running pg_rewind and following timeline switch. You can run bash from extension, what's the point? > The system in hand must be able to manipulate with PGDATA without starting Postgres. -- Best regards, Kirill Reshke ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 05:44 Andrey Borodin <[email protected]> parent: Kirill Reshke <[email protected]> 0 siblings, 1 reply; 36+ messages in thread From: Andrey Borodin @ 2025-04-16 05:44 UTC (permalink / raw) To: Kirill Reshke <[email protected]>; +Cc: Tom Lane <[email protected]>; Konstantin Osipov <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; PostgreSQL Hackers <[email protected]> > On 16 Apr 2025, at 10:39, Kirill Reshke <[email protected]> wrote: > > You can run bash from extension, what's the point? You cannot run bash that will stop backend running bash. Best regards, Andrey Borodin. ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 07:50 Michael Banck <[email protected]> parent: Andrey Borodin <[email protected]> 3 siblings, 0 replies; 36+ messages in thread From: Michael Banck @ 2025-04-16 07:50 UTC (permalink / raw) To: Andrey Borodin <[email protected]>; +Cc: Tom Lane <[email protected]>; Konstantin Osipov <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; PostgreSQL Hackers <[email protected]> Hi, On Wed, Apr 16, 2025 at 10:24:48AM +0500, Andrey Borodin wrote: > I think I can provide some reasons why it cannot be neither extension, > nor any part running within postmaster reign. > > 1. When joining cluster, there’s not PGDATA to run postmaster on top > of it. > > 2. After failover, old Primary node must rejoin cluster by running > pg_rewind and following timeline switch. > > The system in hand must be able to manipulate with PGDATA without > starting Postgres. Yeah, while you could maybe implement some/all of the RAFT protocol in an extension, actually building something useful on top with regards to high availability or distributed whatever does not look feasible. > My question to Konstantin is Why wouldn’t you just add Raft to > Patroni? Patroni can use pysyncobj, which is a Python implementation of RAFT, so then you do not need an external RAFT provider like etcd, consul or zookeeper. However, it is deemed deprecated by the Patroni authors due to being difficult to debug when it breaks. I guess a better Python implementation of RAFT for Patroni to use or Patroni to implement it itself would help, but I believe nobody is working on the latter right now, nor has any plans to do so. And there also does not seem to be anybody working on a better pysyncobj. > Is there a reason why something like Patroni is not in core and noone > rushes to get it in? Everyone is using it, or system like it. Well, Patroni is written in Python, for starters. It also does a lot more than just leader election / cluster config. So I think nobody seriously thought about proposing to put Patroni into core so far. I guess the current proposal tries to be a step into the "something like Patroni in core" if you tilt your head a little. It's just that the whole thing would be a really big step for Postgres, maybe similar to deciding we want in-core replication way back when. Michael ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 09:47 Konstantin Osipov <[email protected]> parent: Nikolay Samokhvalov <[email protected]> 1 sibling, 0 replies; 36+ messages in thread From: Konstantin Osipov @ 2025-04-16 09:47 UTC (permalink / raw) To: Tom Lane <[email protected]>; +Cc: Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; [email protected] * Tom Lane <[email protected]> [25/04/16 11:05]: > Nikolay Samokhvalov <[email protected]> writes: > > This is exactly what I wanted to write as well. The idea is great. At the > > same time, I think, consensus on many decisions will be extremely hard to > > reach, so this project has a high risk of being very long. Unless it's an > > extension, at least in the beginning. > > Yeah. The two questions you'd have to get past to get this into PG > core are: > > 1. Why can't it be an extension? (You claimed it would work more > seamlessly in core, but I don't think you've made a proven case.) I think this can be best addressed when the discussion moves on to an architecture design record, where the UX and implementation details are outlined. I'm sure there can be a lot of bike-shedding on that part. For now I merely wanted to know if: - maybe there is a reason this will never be accepted - maybe someone is already working on this. ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 09:53 Konstantin Osipov <[email protected]> parent: Ashutosh Bapat <[email protected]> 2 siblings, 0 replies; 36+ messages in thread From: Konstantin Osipov @ 2025-04-16 09:53 UTC (permalink / raw) To: Ashutosh Bapat <[email protected]>; +Cc: Andrey Borodin <[email protected]>; Tom Lane <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; [email protected] * Ashutosh Bapat <[email protected]> [25/04/16 11:06]: > > My view is what Konstantin wants is automatic replication topology management. For some reason this technology is called HA, DCS, Raft, Paxos and many other scary words. But basically it manages primary_conn_info of some nodes to provide some fault-tolerance properties. I'd start to design from here, not from Raft paper. > > > In my experience, the load of managing hundreds of replicas which all > participate in RAFT protocol becomes more than regular transaction > load. So making every replica a RAFT participant will affect the > ability to deploy hundreds of replica. I think this experience needs to be detailed out. There are implementations in the field that are less efficient than others. Early etcd-raft didn't have pre-voting and had "bastardized" (their own definition) implementation of configuration changes which didn't use joint consensus. Then there is a liveness issue if leader election is implemented in a straightforward way in large clusters. But this is addressed: scaling up the randomized election timeout with the cluster size, converting most of participants to non-voters in large clusters. Raft replication, again, if implemented in a naive way, would require a O(outstanding transaction) * number of replicas amount of RAM. But that doesn't have to be naive. To sum up, I am not aware of any principal limitations in this area. -- Konstantin Osipov, Moscow, Russia ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 09:58 Konstantin Osipov <[email protected]> parent: Andrey Borodin <[email protected]> 3 siblings, 0 replies; 36+ messages in thread From: Konstantin Osipov @ 2025-04-16 09:58 UTC (permalink / raw) To: Andrey Borodin <[email protected]>; +Cc: Tom Lane <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; PostgreSQL Hackers <[email protected]> * Andrey Borodin <[email protected]> [25/04/16 11:06]: > > Andrey Borodin <[email protected]> writes: > >> I think it's what Konstantin is proposing. To have our own Raft implementation, without dependencies. > > > > Hmm, OK. I thought that the proposal involved relying on some existing > > code, but re-reading the thread that was said nowhere. Still, that > > moves it from a large project to a really large project :-( > > > > I continue to think that it'd be best to try to implement it as > > an extension, at least up till the point of finding show-stopping > > reasons why it cannot be that. > > I think I can provide some reasons why it cannot be neither extension, nor any part running within postmaster reign. > > 1. When joining cluster, there’s not PGDATA to run postmaster on top of it. > > 2. After failover, old Primary node must rejoin cluster by running pg_rewind and following timeline switch. > > The system in hand must be able to manipulate with PGDATA without starting Postgres. > > My question to Konstantin is Why wouldn’t you just add Raft to Patroni? Is there a reason why something like Patroni is not in core and noone rushes to get it in? > Everyone is using it, or system like it. Raft uses the same WAL to store configuration change records as is used for commit records. This is at the core of the correctness of the algorithm. This is also my biggest concern with correctness of Patroni - but to the best of my knowledge 's 90%+ of use cases of Patroni use a "fixed" quorum size, that's defined at start of the deployment and never/rarely changes. Contrast to that being able to a replica to the quorum at any time, and all it takes is just starting this replica and pointing it at the existing cluster. This greatly simplifies UX. -- Konstantin Osipov, Moscow, Russia ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 10:02 Konstantin Osipov <[email protected]> parent: Andrey Borodin <[email protected]> 0 siblings, 0 replies; 36+ messages in thread From: Konstantin Osipov @ 2025-04-16 10:02 UTC (permalink / raw) To: Andrey Borodin <[email protected]>; +Cc: Kirill Reshke <[email protected]>; Tom Lane <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; PostgreSQL Hackers <[email protected]> * Andrey Borodin <[email protected]> [25/04/16 11:06]: > > You can run bash from extension, what's the point? > > You cannot run bash that will stop backend running bash. You're right there is a chicken and egg problem when you add Raft to an existing project, and rebootstrap becomes a trick, but it's a plumbing trick. The new member needs to generate and persist a globally unique identifier as the first step. Later it can reintroduce itself to the cluster given this identifier can be preserved in the new incarnation (popen + fork). -- Konstantin Osipov, Moscow, Russia ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 14:07 Konstantin Osipov <[email protected]> parent: Ashutosh Bapat <[email protected]> 2 siblings, 0 replies; 36+ messages in thread From: Konstantin Osipov @ 2025-04-16 14:07 UTC (permalink / raw) To: Alastair Turner <[email protected]>; +Cc: Ashutosh Bapat <[email protected]>; Andrey Borodin <[email protected]>; Tom Lane <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; PostgreSQL Hackers <[email protected]> * Alastair Turner <[email protected]> [25/04/16 15:58]: > > > If you use build-in failover you have to resort to 3 big Postgres > > machines because you need 2/3 majority. Of course, you can install > > MySQL-stype arbiter - host that had no real PGDATA, only participates in > > voting. But this is a solution to problem induced by built-in autofailover. > > > > Users find it a waste of resources to deploy 3 big PostgreSQL > > instances just for HA where 2 suffice even if they deploy 3 > > lightweight DCS instances. Having only some of the nodes act as DCS > > and others purely PostgreSQL nodes will reduce waste of resources. > > > > The experience of other projects/products with automated failover based on > quorum shows that this is a critical issue for adoption. In the In-memory > Data Grid space (Coherence, Geode/GemFire) the question of how to ensure > that some nodes didn't carry any data comes up early in many architecture > discussions. When RabbitMQ shipped their Quorum Queues feature, the first > and hardest area of pushback was around all nodes hosting message content. > > It's not just about the requirement for compute resources, it's also about > bandwidth and latency. Many large organisations have, for historical > reasons, pairs of data centres with very good point-to-point connectivity. > As the requirement for quorum witnesses has come up for all sorts of > things, including storage arrays, they have built arbiter/witness sites at > branches, colocation providers or even on the public cloud. More than not > holding user data or processing queries, the arbiter can't even be sent the > replication stream for the user data in the database, it just won't fit > down the pipe. > > Which feels like a very difficult requirement to meet if the replication > model for all data is being changed to a quorum model. I agree master/replica deployment layouts are very popular and are not going to directly benefit from raft. They'll still work, but no automation will be available, just like today with Patroni. However, if the storage cost is an argument, then the logical path is to disaggregate storage/compute altogether, i.e. use projects like neon. -- Konstantin Osipov, Moscow, Russia ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 14:29 Yura Sokolov <[email protected]> parent: Andrey Borodin <[email protected]> 3 siblings, 0 replies; 36+ messages in thread From: Yura Sokolov @ 2025-04-16 14:29 UTC (permalink / raw) To: Andrey Borodin <[email protected]>; Tom Lane <[email protected]>; +Cc: Konstantin Osipov <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; PostgreSQL Hackers <[email protected]> 16.04.2025 08:24, Andrey Borodin пишет: > 2. After failover, old Primary node must rejoin cluster by running pg_rewind and following timeline switch. It is really do-able: BiHA already does it. And BiHA runs as a child process of postmaster, ie both postmaster and BiHA doesn't restart when PostgreSQL needs to rewind and restart. Yes, there are non-trivial amount of changes made into postmaster machinery. But it is doable. -- regards Yura Sokolov aka funny-falcon ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 19:29 Greg Sabino Mullane <[email protected]> parent: Ashutosh Bapat <[email protected]> 2 siblings, 1 reply; 36+ messages in thread From: Greg Sabino Mullane @ 2025-04-16 19:29 UTC (permalink / raw) To: Ashutosh Bapat <[email protected]>; +Cc: Andrey Borodin <[email protected]>; Tom Lane <[email protected]>; Konstantin Osipov <[email protected]>; Nikolay Samokhvalov <[email protected]>; PostgreSQL Hackers <[email protected]> On Wed, Apr 16, 2025 at 2:18 AM Ashutosh Bapat <[email protected]> wrote: > Users find it a waste of resources to deploy 3 big PostgreSQL instances > just for HA where 2 suffice even if they deploy 3 lightweight DCS > instances. Having only some of the nodes act as DCS and others purely > PostgreSQL nodes will reduce waste of resources. > A big problem is that putting your DCS into Postgres means your whole system is now super-sensitive to IO/WAL-streaming issues, and a busy database doing database stuff is going to start affecting the DCS stuff. With three lightweight DCS servers, you don't really need to worry about how stressed the database servers are. In that way, I feel etcd et al. are adhering to the unix philosophy of "do one thing, and do it well." Cheers, Greg -- Crunchy Data - https://www.crunchydata.com Enterprise Postgres Software Products & Tech Support ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-16 21:24 Hannu Krosing <[email protected]> parent: Tom Lane <[email protected]> 1 sibling, 0 replies; 36+ messages in thread From: Hannu Krosing @ 2025-04-16 21:24 UTC (permalink / raw) To: Tom Lane <[email protected]>; +Cc: Andrey Borodin <[email protected]>; Konstantin Osipov <[email protected]>; Greg Sabino Mullane <[email protected]>; Nikolay Samokhvalov <[email protected]>; [email protected] On Wed, Apr 16, 2025 at 6:27 AM Tom Lane <[email protected]> wrote: > > Andrey Borodin <[email protected]> writes: > > I think it's what Konstantin is proposing. To have our own Raft implementation, without dependencies. > > Hmm, OK. I thought that the proposal involved relying on some existing > code, but re-reading the thread that was said nowhere. Still, that > moves it from a large project to a really large project :-( My understanding is that RAFT is a fancy name for what PostgreSQL is largely already doing - "electing" a leader and then doing all the changes through that leader (a.k.a. WAL streaming) The thing that needs adding - and which makes it "RAFT" instead of just a streaming replication with a failover - is what happens when the leader goes away and one of the replicas needs to become a new leader. We have ways to do rollbacks and roll-forwards but the main tricky part is "how do you know that you have not lost some changes" and here we must have some place to store the info about at which LSN the failover happened, so that we know to run pg_rewind if any losts hosts come back and want to join. And of course we need to have a way to communicate this "who is the new leader" to clients which needs new libpgq functionality of "failover connection pools" which hide the failovers from old clients. The RAFT protocol could be a provider of "who is current leader info" and optionally cache the LSN the switch happened. > I continue to think that it'd be best to try to implement it as > an extension, at least up till the point of finding show-stopping > reasons why it cannot be that. The main thing I would like to see in core is ability to do clean *switchovers* (not failovers) by sending a magic WAL record with a message "hey node N, please take over the write node role" over WAL so that node N knows to self-promote and all other nodes know to start following N starting from the next WAL record either directly or Why WAL - because it is already is sent to all replicas, it guarantees continuity as it very clearly states at what LSN the write-head-switch happens. We also should be able to send this info to the client libraries currently connected to the writer. so that they can choose to switch to the new head. The rest could be easily an extension. Mainly we want more than one "coordinators" which can be running in some or all of the nodes.and who agree on - which node is current leader - at which LSN the switch happened (so if some node coming back discovers that it has magicall moved ahead it knows to rewind to that LSN and then re-stream it from commonly agreed place. It would also be nice to have some agreed, hopefully lightweight, notion of node identity, which we could then use for many things, including stamping it in WAL records to guarantee / verify that all the nodes have been on the same WAL stream all the time But regarding weather to use RAFT I would just define a "coordinator API" and leave it up to the specific coordinator/consensus extension to decide how the consensus is achieved So to summarize: # Core should provide - way tomove to new node, - for switchover a WAL-based switchover - for failover something similar which also writes the WAL record so all histories are synced - a libpq message informing clients about "new write head node" - node IDs and more general c;luster-awareness inside the PostgreSQL node (I had a shoutout about this in a recent pgconf.dev unconference talk) - a new write-node field in WAL to track write head movement - API for a joining node to find out which cluster it joins and the switchover history - in WAL it is always switchover, maybe with some info saying that it was a forces switchover because we lost old write head - if some lost node comes back it may need to rewind or re-initialize if it finds out it had been following a lost timeline that is not fully part of NOTE: switchovers in WAL would be very similar to timeline changes. I am not sure how much extra info is needed there. # Extension can provide - agreeing on new leader node in case of failover - protocol can be RAFT, PAXOS or "the DBA says so" :) - sharing fresh info about current leader and switch timelines (though this should more likely be in core) - anything else ??? # external apps is (likely?) needed for - setting up cluster, provisioning machines / VMs - setting up networking - starting PostgreSQL servers. - spinning up and down clients, - communicating current leader and replica set (could be done by DNS with agreed conventions) ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: Built-in Raft replication @ 2025-04-29 20:16 Jim Nasby <[email protected]> parent: Greg Sabino Mullane <[email protected]> 0 siblings, 0 replies; 36+ messages in thread From: Jim Nasby @ 2025-04-29 20:16 UTC (permalink / raw) To: Devrim Gündüz <[email protected]>; +Cc: Greg Sabino Mullane <[email protected]>; Ashutosh Bapat <[email protected]>; Andrey Borodin <[email protected]>; Tom Lane <[email protected]>; Konstantin Osipov <[email protected]>; Nikolay Samokhvalov <[email protected]>; PostgreSQL Hackers <[email protected]> I've always assumed there'd have to be at least one global stream, if for no other purpose than to be the source of truth about transaction commit ordering (though, I was thinking of supporting multiple streams for one database). Presumably the same could be used for shared objects. Or perhaps shared objects just get their own stream. Either way, having a master commit record that points at LSNs of various other streams is what I'd been thinking. On Wed, Apr 23, 2025 at 12:01 PM Devrim Gündüz <[email protected]> wrote: > Hi, > > On Wed, 2025-04-23 at 11:48 -0500, Jim Nasby wrote: > > unless we added multiple WAL streams. That would allow for splitting > > WAL traffic across multiple devices as well as providing better > > support for configurations that don’t replicate the entire cluster. > > The current situation where delayed replication of a single table > > mandates retention of all the WAL for the entire cluster is less than > > ideal. > > I think the problem is handling the stream of global objects. Having > separate stream for each database would be awesome as long as it can > deal with the "global stream". > > Regards, > -- > Devrim Gündüz > Open Source Solution Architect, PostgreSQL Major Contributor > BlueSky: @devrim.gunduz.org , @gunduz.org > ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: use of SPI by postgresImportForeignStatistics @ 2026-07-10 05:03 Etsuro Fujita <[email protected]> 0 siblings, 1 reply; 36+ messages in thread From: Etsuro Fujita @ 2026-07-10 05:03 UTC (permalink / raw) To: Corey Huinker <[email protected]>; +Cc: Robert Haas <[email protected]>; pgsql-hackers On Wed, Jul 8, 2026 at 9:04 PM Etsuro Fujita <[email protected]> wrote: > Attached is a new version > of the patch. I'm planning to push and back-patch it, if no > objections. Committed and back-patched. Best regards, Etsuro Fujita ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: use of SPI by postgresImportForeignStatistics @ 2026-07-10 05:36 Fujii Masao <[email protected]> parent: Etsuro Fujita <[email protected]> 0 siblings, 1 reply; 36+ messages in thread From: Fujii Masao @ 2026-07-10 05:36 UTC (permalink / raw) To: Etsuro Fujita <[email protected]>; +Cc: Corey Huinker <[email protected]>; Robert Haas <[email protected]>; pgsql-hackers On Fri, Jul 10, 2026 at 2:03 PM Etsuro Fujita <[email protected]> wrote: > > On Wed, Jul 8, 2026 at 9:04 PM Etsuro Fujita <[email protected]> wrote: > > Attached is a new version > > of the patch. I'm planning to push and back-patch it, if no > > objections. > > Committed and back-patched. In the committed patch, I found that the set_*_arg() helper functions in postgres_fdw.c are declared static in their prototypes, but their definitions omit the static keyword. This looks like an oversight. Attached patch adds static to the definitions for consistency and to make their intended file-local scope explicit. It also fixes a few nearby comment typos. Regards, -- Fujii Masao Attachments: [application/octet-stream] v1-0001-postgres_fdw-Mark-statistics-import-helpers-as-st.patch (3.4K, ../../CAHGQGwGjcQ4SwHMUQ9P8UYQ7iLKL1QE3uLSdONToQ1MrzpUUoQ@mail.gmail.com/2-v1-0001-postgres_fdw-Mark-statistics-import-helpers-as-st.patch) download | inline diff: From f9793e5fe924b49e1cad93f7d33ed313283c51f7 Mon Sep 17 00:00:00 2001 From: Fujii Masao <[email protected]> Date: Fri, 10 Jul 2026 14:22:54 +0900 Subject: [PATCH v1] postgres_fdw: Mark statistics import helpers as static The set_*_arg helper functions in postgres_fdw.c are declared static, but their definitions omitted the static keyword. Add it to make their file-local scope explicit and keep the declarations and definitions consistent. Also fix a couple of nearby comment typos. --- contrib/postgres_fdw/postgres_fdw.c | 12 ++++++------ src/backend/statistics/attribute_stats.c | 2 +- src/backend/statistics/relation_stats.c | 2 +- 3 files changed, 8 insertions(+), 8 deletions(-) diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c index e6e0a4ab9b5..70de942de12 100644 --- a/contrib/postgres_fdw/postgres_fdw.c +++ b/contrib/postgres_fdw/postgres_fdw.c @@ -6134,7 +6134,7 @@ import_fetched_statistics(Relation relation, } /* - * Conenience routine to fetch the value for the row/column of the PGresult + * Convenience routine to fetch the value for the row/column of the PGresult */ static char * get_opt_value(PGresult *res, int row, int col) @@ -6147,7 +6147,7 @@ get_opt_value(PGresult *res, int row, int col) /* * Convenience routine for setting optional text arguments */ -void +static void set_text_arg(NullableDatum *arg, const char *s) { if (s) @@ -6165,7 +6165,7 @@ set_text_arg(NullableDatum *arg, const char *s) /* * Convenience routine for setting optional int32 arguments */ -void +static void set_int32_arg(NullableDatum *arg, const char *s) { if (s) @@ -6185,7 +6185,7 @@ set_int32_arg(NullableDatum *arg, const char *s) /* * Convenience routine for setting optional uint32 arguments */ -void +static void set_uint32_arg(NullableDatum *arg, const char *s) { if (s) @@ -6205,7 +6205,7 @@ set_uint32_arg(NullableDatum *arg, const char *s) /* * Convenience routine for setting optional float arguments */ -void +static void set_float_arg(NullableDatum *arg, const char *s) { if (s) @@ -6225,7 +6225,7 @@ set_float_arg(NullableDatum *arg, const char *s) /* * Convenience routine for setting optional float[] arguments */ -void +static void set_floatarr_arg(NullableDatum *arg, const char *s) { if (s) diff --git a/src/backend/statistics/attribute_stats.c b/src/backend/statistics/attribute_stats.c index 2efb74b95a6..48e0df391e2 100644 --- a/src/backend/statistics/attribute_stats.c +++ b/src/backend/statistics/attribute_stats.c @@ -708,7 +708,7 @@ pg_restore_attribute_stats(PG_FUNCTION_ARGS) } /* - * Import attribute statistics from NullableDatum inputs for all statitical + * Import attribute statistics from NullableDatum inputs for all statistical * values. * * For now, the 'version' argument is ignored. In the future it can be used diff --git a/src/backend/statistics/relation_stats.c b/src/backend/statistics/relation_stats.c index 990a7511d04..fbaab92284f 100644 --- a/src/backend/statistics/relation_stats.c +++ b/src/backend/statistics/relation_stats.c @@ -256,7 +256,7 @@ pg_restore_relation_stats(PG_FUNCTION_ARGS) } /* - * Import relation statistics from NullableDatum inputs for all statitical + * Import relation statistics from NullableDatum inputs for all statistical * values. * * For now, the 'version' argument is ignored. In the future it can be used -- 2.55.0 ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: use of SPI by postgresImportForeignStatistics @ 2026-07-10 07:40 Etsuro Fujita <[email protected]> parent: Fujii Masao <[email protected]> 0 siblings, 1 reply; 36+ messages in thread From: Etsuro Fujita @ 2026-07-10 07:40 UTC (permalink / raw) To: Fujii Masao <[email protected]>; +Cc: Corey Huinker <[email protected]>; Robert Haas <[email protected]>; pgsql-hackers Fujii-san, On Fri, Jul 10, 2026 at 2:37 PM Fujii Masao <[email protected]> wrote: > In the committed patch, I found that the set_*_arg() helper functions > in postgres_fdw.c are declared static in their prototypes, but their > definitions omit the static keyword. This looks like an oversight. > > Attached patch adds static to the definitions for consistency and > to make their intended file-local scope explicit. It also fixes a few > nearby comment typos. Good catch! Thanks for the patch! LGTM. Best regards, Etsuro Fujita ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: use of SPI by postgresImportForeignStatistics @ 2026-07-10 11:36 Etsuro Fujita <[email protected]> parent: Etsuro Fujita <[email protected]> 0 siblings, 2 replies; 36+ messages in thread From: Etsuro Fujita @ 2026-07-10 11:36 UTC (permalink / raw) To: Fujii Masao <[email protected]>; +Cc: Corey Huinker <[email protected]>; Robert Haas <[email protected]>; pgsql-hackers On Fri, Jul 10, 2026 at 4:40 PM Etsuro Fujita <[email protected]> wrote: > On Fri, Jul 10, 2026 at 2:37 PM Fujii Masao <[email protected]> wrote: > > In the committed patch, I found that the set_*_arg() helper functions > > in postgres_fdw.c are declared static in their prototypes, but their > > definitions omit the static keyword. This looks like an oversight. > > > > Attached patch adds static to the definitions for consistency and > > to make their intended file-local scope explicit. It also fixes a few > > nearby comment typos. > > Good catch! Thanks for the patch! LGTM. My compiler (Apple clang version 17.0.0 (clang-1700.4.4.1)) doesn't output any error/warning about that declaration. Actually, it's allowed? Anyway, +1 for adding it for consistency. Best regards, Etsuro Fujita ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: use of SPI by postgresImportForeignStatistics @ 2026-07-10 12:09 Fujii Masao <[email protected]> parent: Etsuro Fujita <[email protected]> 1 sibling, 0 replies; 36+ messages in thread From: Fujii Masao @ 2026-07-10 12:09 UTC (permalink / raw) To: Etsuro Fujita <[email protected]>; +Cc: Corey Huinker <[email protected]>; Robert Haas <[email protected]>; pgsql-hackers On Fri, Jul 10, 2026 at 8:37 PM Etsuro Fujita <[email protected]> wrote: > > On Fri, Jul 10, 2026 at 4:40 PM Etsuro Fujita <[email protected]> wrote: > > On Fri, Jul 10, 2026 at 2:37 PM Fujii Masao <[email protected]> wrote: > > > In the committed patch, I found that the set_*_arg() helper functions > > > in postgres_fdw.c are declared static in their prototypes, but their > > > definitions omit the static keyword. This looks like an oversight. > > > > > > Attached patch adds static to the definitions for consistency and > > > to make their intended file-local scope explicit. It also fixes a few > > > nearby comment typos. > > > > Good catch! Thanks for the patch! LGTM. > > My compiler (Apple clang version 17.0.0 (clang-1700.4.4.1)) doesn't > output any error/warning about that declaration. Actually, it's > allowed? Anyway, +1 for adding it for consistency. Maybe that's allowed. I wonder adding static to both the declaration and the definition seems mainly a matter of consistency, readability, and coding style. Thanks for the review! I've pushed the patch. Regards, -- Fujii Masao ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: use of SPI by postgresImportForeignStatistics @ 2026-07-10 14:08 Tom Lane <[email protected]> parent: Etsuro Fujita <[email protected]> 1 sibling, 1 reply; 36+ messages in thread From: Tom Lane @ 2026-07-10 14:08 UTC (permalink / raw) To: Etsuro Fujita <[email protected]>; +Cc: Fujii Masao <[email protected]>; Corey Huinker <[email protected]>; Robert Haas <[email protected]>; pgsql-hackers Etsuro Fujita <[email protected]> writes: > On Fri, Jul 10, 2026 at 4:40 PM Etsuro Fujita <[email protected]> wrote: >> On Fri, Jul 10, 2026 at 2:37 PM Fujii Masao <[email protected]> wrote: >>> Attached patch adds static to the definitions for consistency and >>> to make their intended file-local scope explicit. It also fixes a few >>> nearby comment typos. > My compiler (Apple clang version 17.0.0 (clang-1700.4.4.1)) doesn't > output any error/warning about that declaration. Actually, it's > allowed? Anyway, +1 for adding it for consistency. The back story here is that that coding pattern is allowed by standard C but traditionally (pre-ANSI C or so) wasn't. We used to have some buildfarm animals that would warn about it, but none do today. I think it's a good idea to include "static" in the definitions for clarity, and so that you don't have to go looking for the declaration to know if a function is file-local or not. But the standard doesn't require that. Rummaging in the gcc manual, it looks like you can turn on a warning for this with '-Wtraditional', but that also enables a boatload of warnings we don't want, so I can't see using it on a regular basis. regards, tom lane ^ permalink raw reply [nested|flat] 36+ messages in thread
* Re: use of SPI by postgresImportForeignStatistics @ 2026-07-10 14:41 Tom Lane <[email protected]> parent: Tom Lane <[email protected]> 0 siblings, 0 replies; 36+ messages in thread From: Tom Lane @ 2026-07-10 14:41 UTC (permalink / raw) To: Etsuro Fujita <[email protected]>; +Cc: Fujii Masao <[email protected]>; Corey Huinker <[email protected]>; Robert Haas <[email protected]>; pgsql-hackers I wrote: > Rummaging in the gcc manual, it looks like you can turn on a warning > for this with '-Wtraditional', but that also enables a boatload of > warnings we don't want, so I can't see using it on a regular basis. I experimented with that for fun. On current HEAD, it produces 347111 warnings, mostly "traditional C rejects ISO C style function definitions". But amongst the dross there's dbcommands.c:395:1: warning: non-static declaration of 'ScanSourceDatabasePgClassTuple' follows static declaration [-Wtraditional] event_trigger.c:392:1: warning: non-static declaration of 'SetDatabaseHasLoginEventTriggers' follows static declaration [-Wtraditional] tablecmds.c:20846:1: warning: non-static declaration of 'ConstraintImpliedByRelConstraint' follows static declaration [-Wtraditional] nodeModifyTable.c:4154:1: warning: non-static declaration of 'ExecInitMerge' follows static declaration [-Wtraditional] postmaster.c:4056:1: warning: non-static declaration of 'StartSysLogger' follows static declaration [-Wtraditional] buf_table.c:48:1: warning: non-static declaration of 'BufTableShmemRequest' follows static declaration [-Wtraditional] oracle_compat.c:555:1: warning: non-static declaration of 'dobyteatrim' follows static declaration [-Wtraditional] pg_locale_icu.c:746:1: warning: non-static declaration of 'strncoll_icu_utf8' follows static declaration [-Wtraditional] pg_locale_icu.c:767:1: warning: non-static declaration of 'strcoll_icu_utf8' follows static declaration [-Wtraditional] pg_walsummary.c:230:1: warning: non-static declaration of 'walsummary_error_callback' follows static declaration [-Wtraditional] pg_walsummary.c:245:1: warning: non-static declaration of 'walsummary_read_callback' follows static declaration [-Wtraditional] vacuumdb.c:327:1: warning: non-static declaration of 'check_objfilter' follows static declaration [-Wtraditional] if anyone cares to follow that up. regards, tom lane ^ permalink raw reply [nested|flat] 36+ messages in thread
end of thread, other threads:[~2026-07-10 14:41 UTC | newest] Thread overview: 36+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2020-09-12 13:07 [PATCH 2/8] Pass all scan keys to BRIN consistent function at once Tomas Vondra <[email protected]> 2025-04-14 17:15 Built-in Raft replication Konstantin Osipov <[email protected]> 2025-04-14 17:44 ` Re: Built-in Raft replication Kirill Reshke <[email protected]> 2025-04-14 19:00 ` Re: Built-in Raft replication Konstantin Osipov <[email protected]> 2025-04-15 11:14 ` Re: Built-in Raft replication Konstantin Osipov <[email protected]> 2025-04-15 10:20 ` Re: Built-in Raft replication Aleksander Alekseev <[email protected]> 2025-04-15 11:15 ` Re: Built-in Raft replication Aleksander Alekseev <[email protected]> 2025-04-15 11:20 ` Re: Built-in Raft replication Yura Sokolov <[email protected]> 2025-04-15 11:23 ` Re: Built-in Raft replication Konstantin Osipov <[email protected]> 2025-04-15 11:24 ` Re: Built-in Raft replication Konstantin Osipov <[email protected]> 2025-04-15 15:07 ` Re: Built-in Raft replication Greg Sabino Mullane <[email protected]> 2025-04-15 17:27 ` Re: Built-in Raft replication Konstantin Osipov <[email protected]> 2025-04-15 22:27 ` Re: Built-in Raft replication Nikolay Samokhvalov <[email protected]> 2025-04-16 04:07 ` Re: Built-in Raft replication Andrey Borodin <[email protected]> 2025-04-16 04:26 ` Re: Built-in Raft replication Tom Lane <[email protected]> 2025-04-16 05:24 ` Re: Built-in Raft replication Andrey Borodin <[email protected]> 2025-04-16 05:39 ` Re: Built-in Raft replication Kirill Reshke <[email protected]> 2025-04-16 05:44 ` Re: Built-in Raft replication Andrey Borodin <[email protected]> 2025-04-16 10:02 ` Re: Built-in Raft replication Konstantin Osipov <[email protected]> 2025-04-16 07:50 ` Re: Built-in Raft replication Michael Banck <[email protected]> 2025-04-16 09:58 ` Re: Built-in Raft replication Konstantin Osipov <[email protected]> 2025-04-16 14:29 ` Re: Built-in Raft replication Yura Sokolov <[email protected]> 2025-04-16 21:24 ` Re: Built-in Raft replication Hannu Krosing <[email protected]> 2025-04-16 04:33 ` Re: Built-in Raft replication Ashutosh Bapat <[email protected]> 2025-04-16 09:53 ` Re: Built-in Raft replication Konstantin Osipov <[email protected]> 2025-04-16 14:07 ` Re: Built-in Raft replication Konstantin Osipov <[email protected]> 2025-04-16 19:29 ` Re: Built-in Raft replication Greg Sabino Mullane <[email protected]> 2025-04-29 20:16 ` Re: Built-in Raft replication Jim Nasby <[email protected]> 2025-04-16 09:47 ` Re: Built-in Raft replication Konstantin Osipov <[email protected]> 2026-07-10 05:03 Re: use of SPI by postgresImportForeignStatistics Etsuro Fujita <[email protected]> 2026-07-10 05:36 ` Re: use of SPI by postgresImportForeignStatistics Fujii Masao <[email protected]> 2026-07-10 07:40 ` Re: use of SPI by postgresImportForeignStatistics Etsuro Fujita <[email protected]> 2026-07-10 11:36 ` Re: use of SPI by postgresImportForeignStatistics Etsuro Fujita <[email protected]> 2026-07-10 12:09 ` Re: use of SPI by postgresImportForeignStatistics Fujii Masao <[email protected]> 2026-07-10 14:08 ` Re: use of SPI by postgresImportForeignStatistics Tom Lane <[email protected]> 2026-07-10 14:41 ` Re: use of SPI by postgresImportForeignStatistics Tom Lane <[email protected]>
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