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* [PATCH 03/10] Make sure published XIDs are persistent
@ 2021-03-08 06:43 Kyotaro Horiguchi <[email protected]>
0 siblings, 0 replies; 3+ messages in thread
From: Kyotaro Horiguchi @ 2021-03-08 06:43 UTC (permalink / raw)
pg_xact_status() premises that XIDs obtained by
pg_current_xact_id(_if_assigned)() are persistent beyond a crash. But
XIDs are not guaranteed to go beyond WAL buffers before commit and
thus XIDs may vanish if server crashes before commit. This patch
guarantees the XID shown by the functions to be flushed out to disk.
Copied from: https://www.postgresql.org/message-id/20210308.173242.463790587797836129.horikyota.ntt%40gmail.com
---
src/backend/access/transam/xact.c | 55 +++++++++++++++++++++++++------
src/backend/access/transam/xlog.c | 2 +-
src/backend/utils/adt/xid8funcs.c | 12 ++++++-
src/include/access/xact.h | 3 +-
4 files changed, 59 insertions(+), 13 deletions(-)
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 6395a9b240..38e978d238 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -201,7 +201,7 @@ typedef struct TransactionStateData
int prevSecContext; /* previous SecurityRestrictionContext */
bool prevXactReadOnly; /* entry-time xact r/o state */
bool startedInRecovery; /* did we start in recovery? */
- bool didLogXid; /* has xid been included in WAL record? */
+ XLogRecPtr minLSN; /* LSN needed to reach to record the xid */
int parallelModeLevel; /* Enter/ExitParallelMode counter */
bool chain; /* start a new block after this one */
bool assigned; /* assigned to top-level XID */
@@ -520,14 +520,46 @@ GetCurrentFullTransactionIdIfAny(void)
* MarkCurrentTransactionIdLoggedIfAny
*
* Remember that the current xid - if it is assigned - now has been wal logged.
+ *
+ * upto is the LSN up to which we need to flush WAL to ensure the current xid
+ * to be persistent. See EnsureCurrentTransactionIdLogged().
*/
void
-MarkCurrentTransactionIdLoggedIfAny(void)
+MarkCurrentTransactionIdLoggedIfAny(XLogRecPtr upto)
{
- if (FullTransactionIdIsValid(CurrentTransactionState->fullTransactionId))
- CurrentTransactionState->didLogXid = true;
+ if (FullTransactionIdIsValid(CurrentTransactionState->fullTransactionId) &&
+ XLogRecPtrIsInvalid(CurrentTransactionState->minLSN))
+ CurrentTransactionState->minLSN = upto;
}
+/*
+ * EnsureCurrentTransactionIdLogged
+ *
+ * Make sure that the current top XID is WAL-logged.
+ */
+void
+EnsureTopTransactionIdLogged(void)
+{
+ /*
+ * We need at least one WAL record for the current top transaction to be
+ * flushed out. Write one if we don't have one yet.
+ */
+ if (XLogRecPtrIsInvalid(TopTransactionStateData.minLSN))
+ {
+ xl_xact_assignment xlrec;
+
+ xlrec.xtop = XidFromFullTransactionId(XactTopFullTransactionId);
+ Assert(TransactionIdIsValid(xlrec.xtop));
+ xlrec.nsubxacts = 0;
+
+ XLogBeginInsert();
+ XLogRegisterData((char *) &xlrec, MinSizeOfXactAssignment);
+ TopTransactionStateData.minLSN =
+ XLogInsert(RM_XACT_ID, XLOG_XACT_ASSIGNMENT);
+ }
+
+ XLogFlush(TopTransactionStateData.minLSN);
+}
/*
* GetStableLatestTransactionId
@@ -616,14 +648,14 @@ AssignTransactionId(TransactionState s)
* When wal_level=logical, guarantee that a subtransaction's xid can only
* be seen in the WAL stream if its toplevel xid has been logged before.
* If necessary we log an xact_assignment record with fewer than
- * PGPROC_MAX_CACHED_SUBXIDS. Note that it is fine if didLogXid isn't set
+ * PGPROC_MAX_CACHED_SUBXIDS. Note that it is fine if minLSN isn't set
* for a transaction even though it appears in a WAL record, we just might
* superfluously log something. That can happen when an xid is included
* somewhere inside a wal record, but not in XLogRecord->xl_xid, like in
* xl_standby_locks.
*/
if (isSubXact && XLogLogicalInfoActive() &&
- !TopTransactionStateData.didLogXid)
+ XLogRecPtrIsInvalid(TopTransactionStateData.minLSN))
log_unknown_top = true;
/*
@@ -693,6 +725,7 @@ AssignTransactionId(TransactionState s)
log_unknown_top)
{
xl_xact_assignment xlrec;
+ XLogRecPtr endptr;
/*
* xtop is always set by now because we recurse up transaction
@@ -707,11 +740,13 @@ AssignTransactionId(TransactionState s)
XLogRegisterData((char *) unreportedXids,
nUnreportedXids * sizeof(TransactionId));
- (void) XLogInsert(RM_XACT_ID, XLOG_XACT_ASSIGNMENT);
+ endptr = XLogInsert(RM_XACT_ID, XLOG_XACT_ASSIGNMENT);
nUnreportedXids = 0;
- /* mark top, not current xact as having been logged */
- TopTransactionStateData.didLogXid = true;
+
+ /* set minLSN of top, not of current xact if not yet */
+ if (XLogRecPtrIsInvalid(TopTransactionStateData.minLSN))
+ TopTransactionStateData.minLSN = endptr;
}
}
}
@@ -2022,7 +2057,7 @@ StartTransaction(void)
* initialize reported xid accounting
*/
nUnreportedXids = 0;
- s->didLogXid = false;
+ s->minLSN = InvalidXLogRecPtr;
/*
* must initialize resource-management stuff first
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 15da91a8dd..6eb46ea8a7 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -1172,7 +1172,7 @@ XLogInsertRecord(XLogRecData *rdata,
*/
WALInsertLockRelease();
- MarkCurrentTransactionIdLoggedIfAny();
+ MarkCurrentTransactionIdLoggedIfAny(EndPos);
END_CRIT_SECTION();
diff --git a/src/backend/utils/adt/xid8funcs.c b/src/backend/utils/adt/xid8funcs.c
index cc2b4ac797..992482f8c8 100644
--- a/src/backend/utils/adt/xid8funcs.c
+++ b/src/backend/utils/adt/xid8funcs.c
@@ -357,6 +357,8 @@ bad_format:
Datum
pg_current_xact_id(PG_FUNCTION_ARGS)
{
+ FullTransactionId xid;
+
/*
* Must prevent during recovery because if an xid is not assigned we try
* to assign one, which would fail. Programs already rely on this function
@@ -365,7 +367,12 @@ pg_current_xact_id(PG_FUNCTION_ARGS)
*/
PreventCommandDuringRecovery("pg_current_xact_id()");
- PG_RETURN_FULLTRANSACTIONID(GetTopFullTransactionId());
+ xid = GetTopFullTransactionId();
+
+ /* the XID is going to be published, make sure it is psersistent */
+ EnsureTopTransactionIdLogged();
+
+ PG_RETURN_FULLTRANSACTIONID(xid);
}
/*
@@ -380,6 +387,9 @@ pg_current_xact_id_if_assigned(PG_FUNCTION_ARGS)
if (!FullTransactionIdIsValid(topfxid))
PG_RETURN_NULL();
+ /* the XID is going to be published, make sure it is psersistent */
+ EnsureTopTransactionIdLogged();
+
PG_RETURN_FULLTRANSACTIONID(topfxid);
}
diff --git a/src/include/access/xact.h b/src/include/access/xact.h
index 34cfaf542c..a61e4d6da5 100644
--- a/src/include/access/xact.h
+++ b/src/include/access/xact.h
@@ -386,7 +386,8 @@ extern FullTransactionId GetTopFullTransactionId(void);
extern FullTransactionId GetTopFullTransactionIdIfAny(void);
extern FullTransactionId GetCurrentFullTransactionId(void);
extern FullTransactionId GetCurrentFullTransactionIdIfAny(void);
-extern void MarkCurrentTransactionIdLoggedIfAny(void);
+extern void MarkCurrentTransactionIdLoggedIfAny(XLogRecPtr upto);
+extern void EnsureTopTransactionIdLogged(void);
extern bool SubTransactionIsActive(SubTransactionId subxid);
extern CommandId GetCurrentCommandId(bool used);
extern void SetParallelStartTimestamps(TimestampTz xact_ts, TimestampTz stmt_ts);
--
2.17.0
--XsQoSWH+UP9D9v3l
Content-Type: text/x-diff; charset=us-ascii
Content-Disposition: attachment;
filename="0004-wal_compression_method-default-to-zlib.patch"
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Docs: Encourage strong server verification with SCRAM
@ 2023-05-25 17:29 Stephen Frost <[email protected]>
0 siblings, 1 reply; 3+ messages in thread
From: Stephen Frost @ 2023-05-25 17:29 UTC (permalink / raw)
To: Jacob Champion <[email protected]>; +Cc: Daniel Gustafsson <[email protected]>; PostgreSQL Hackers <[email protected]>; Jonathan S. Katz <[email protected]>; Michael Paquier <[email protected]>
Greetings,
* Jacob Champion ([email protected]) wrote:
> On 5/24/23 05:04, Daniel Gustafsson wrote:
> >> On 23 May 2023, at 23:02, Stephen Frost <[email protected]> wrote:
> >> Perhaps more succinctly- maybe we should be making adjustments to the
> >> current language instead of just adding a new paragraph.
> >
> > +1
>
> I'm 100% on board for doing that as well, but the "instead of"
> suggestion makes me think I didn't explain my goal very well. For
> example, Stephen, you said
>
> > I have to admit that the patch as presented strikes me as a warning
> > without really providing steps for how to address the issues mentioned
> > though; there's a reference to what was just covered at the bottom but
> > nothing really new.
>
> but the last sentence of my patch *is* the suggested step:
>
> > + ... It's recommended to employ strong server
> > + authentication, using one of the above anti-spoofing measures, to prevent
> > + these attacks.
I was referring specifically to that ordering as not being ideal or in
line with the rest of the flow of that section. We should integrate the
concerns higher in the section where we outline the reason these things
matter and then follow those with the specific steps for how to address
them, not give a somewhat unclear reference from the very bottom back up
to something above.
Thanks,
Stephen
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^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Docs: Encourage strong server verification with SCRAM
@ 2023-05-25 17:45 Jacob Champion <[email protected]>
parent: Stephen Frost <[email protected]>
0 siblings, 0 replies; 3+ messages in thread
From: Jacob Champion @ 2023-05-25 17:45 UTC (permalink / raw)
To: Stephen Frost <[email protected]>; +Cc: Daniel Gustafsson <[email protected]>; PostgreSQL Hackers <[email protected]>; Jonathan S. Katz <[email protected]>; Michael Paquier <[email protected]>
On Thu, May 25, 2023 at 10:29 AM Stephen Frost <[email protected]> wrote:
> I was referring specifically to that ordering as not being ideal or in
> line with the rest of the flow of that section. We should integrate the
> concerns higher in the section where we outline the reason these things
> matter and then follow those with the specific steps for how to address
> them, not give a somewhat unclear reference from the very bottom back up
> to something above.
Ah, I misunderstood. I'll give that a shot.
Thanks!
--Jacob
^ permalink raw reply [nested|flat] 3+ messages in thread
end of thread, other threads:[~2023-05-25 17:45 UTC | newest]
Thread overview: 3+ messages (download: mbox mbox.gz follow: Atom feed)
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2021-03-08 06:43 [PATCH 03/10] Make sure published XIDs are persistent Kyotaro Horiguchi <[email protected]>
2023-05-25 17:29 Re: Docs: Encourage strong server verification with SCRAM Stephen Frost <[email protected]>
2023-05-25 17:45 ` Re: Docs: Encourage strong server verification with SCRAM Jacob Champion <[email protected]>
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