pg.ddx.io pgsql-hackers@postgresql.org mailing list archive help / color / mirror / Atom feed From: Nathan Bossart <nathandbossart@gmail.com>
To: Rahila Syed <rahilasyed90@gmail.com>
Cc: Sami Imseih <samimseih@gmail.com>
Cc: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Improve LWLock tranche name visibility across backends
Date: Thu, 4 Sep 2025 10:44:00 -0500
Message-ID: <aLmzwC2dRbqk14y6@nathan> (raw )
In-Reply-To: <aLiQeizOQKbKF-ae@nathan >
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<aLCEo0ZMV3vIGRWk@nathan >
<CAA5RZ0vw-r1qjHw5hUNTzAyCiK3KQ-r+G5ECfWSn+qjdu-fpnw@mail.gmail.com >
<aLHO-jh-spXWG1pt@nathan >
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<CAH2L28sz2NcLCS2v1MNkBNUiTiO=-CegFGdAvO24nE+hbjzgjQ@mail.gmail.com >
<aLcPbyWLawp5_rdt@nathan >
<aLiQeizOQKbKF-ae@nathan >
On Wed, Sep 03, 2025 at 02:01:14PM -0500, Nathan Bossart wrote:
> Committed.
I'm having some regrets about the changes to RequestNamedLWLockTranche().
Specifically, when it is first called, it immediately allocates an array
big enough to hold 256 requests (~17 KB), whereas it used to only allocate
space for 16 requests (~1 KB) and resize as needed. Furthermore, the
MAX_NAMED_TRANCHES check isn't actually needed because InitializeLWLocks()
will do the same check via its calls to LWLockNewTrancheId() for all the
named tranche requests.
--
nathan
From 6fe6590f86427c55ac831c5b48784d3d259fe1c8 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Thu, 4 Sep 2025 10:36:06 -0500
Subject: [PATCH v1 1/1] Revert some recent changes to
RequestNamedLWLockTranche().
---
src/backend/storage/lmgr/lwlock.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 258cdebd0f5..a5f6b81806d 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -610,6 +610,7 @@ void
RequestNamedLWLockTranche(const char *tranche_name, int num_lwlocks)
{
NamedLWLockTrancheRequest *request;
+ static int NamedLWLockTrancheRequestsAllocated;
if (!process_shmem_requests_in_progress)
elog(FATAL, "cannot request additional LWLocks outside shmem_request_hook");
@@ -628,17 +629,22 @@ RequestNamedLWLockTranche(const char *tranche_name, int num_lwlocks)
if (NamedLWLockTrancheRequestArray == NULL)
{
+ NamedLWLockTrancheRequestsAllocated = 16;
NamedLWLockTrancheRequestArray = (NamedLWLockTrancheRequest *)
MemoryContextAlloc(TopMemoryContext,
MAX_NAMED_TRANCHES
* sizeof(NamedLWLockTrancheRequest));
}
- if (NamedLWLockTrancheRequests >= MAX_NAMED_TRANCHES)
- ereport(ERROR,
- (errmsg("maximum number of tranches already registered"),
- errdetail("No more than %d tranches may be registered.",
- MAX_NAMED_TRANCHES)));
+ if (NamedLWLockTrancheRequests >= NamedLWLockTrancheRequestsAllocated)
+ {
+ int i = pg_nextpower2_32(NamedLWLockTrancheRequests + 1);
+
+ NamedLWLockTrancheRequestArray = (NamedLWLockTrancheRequest *)
+ repalloc(NamedLWLockTrancheRequestArray,
+ i * sizeof(NamedLWLockTrancheRequest));
+ NamedLWLockTrancheRequestsAllocated = i;
+ }
request = &NamedLWLockTrancheRequestArray[NamedLWLockTrancheRequests];
strlcpy(request->tranche_name, tranche_name, NAMEDATALEN);
--
2.39.5 (Apple Git-154)
Attachments:
v1-0001-Revert-some-recent-changes-to-RequestNamedLWLockT.patch (text/plain, 1.9K) download
From 6fe6590f86427c55ac831c5b48784d3d259fe1c8 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Thu, 4 Sep 2025 10:36:06 -0500
Subject: [PATCH v1 1/1] Revert some recent changes to
RequestNamedLWLockTranche().
---
src/backend/storage/lmgr/lwlock.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)
diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c
index 258cdebd0f5..a5f6b81806d 100644
--- a/src/backend/storage/lmgr/lwlock.c
+++ b/src/backend/storage/lmgr/lwlock.c
@@ -610,6 +610,7 @@ void
RequestNamedLWLockTranche(const char *tranche_name, int num_lwlocks)
{
NamedLWLockTrancheRequest *request;
+ static int NamedLWLockTrancheRequestsAllocated;
if (!process_shmem_requests_in_progress)
elog(FATAL, "cannot request additional LWLocks outside shmem_request_hook");
@@ -628,17 +629,22 @@ RequestNamedLWLockTranche(const char *tranche_name, int num_lwlocks)
if (NamedLWLockTrancheRequestArray == NULL)
{
+ NamedLWLockTrancheRequestsAllocated = 16;
NamedLWLockTrancheRequestArray = (NamedLWLockTrancheRequest *)
MemoryContextAlloc(TopMemoryContext,
MAX_NAMED_TRANCHES
* sizeof(NamedLWLockTrancheRequest));
}
- if (NamedLWLockTrancheRequests >= MAX_NAMED_TRANCHES)
- ereport(ERROR,
- (errmsg("maximum number of tranches already registered"),
- errdetail("No more than %d tranches may be registered.",
- MAX_NAMED_TRANCHES)));
+ if (NamedLWLockTrancheRequests >= NamedLWLockTrancheRequestsAllocated)
+ {
+ int i = pg_nextpower2_32(NamedLWLockTrancheRequests + 1);
+
+ NamedLWLockTrancheRequestArray = (NamedLWLockTrancheRequest *)
+ repalloc(NamedLWLockTrancheRequestArray,
+ i * sizeof(NamedLWLockTrancheRequest));
+ NamedLWLockTrancheRequestsAllocated = i;
+ }
request = &NamedLWLockTrancheRequestArray[NamedLWLockTrancheRequests];
strlcpy(request->tranche_name, tranche_name, NAMEDATALEN);
--
2.39.5 (Apple Git-154)
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To: pgsql-hackers@postgresql.org
Cc: nathandbossart@gmail.com, rahilasyed90@gmail.com, samimseih@gmail.com, bertranddrouvot.pg@gmail.com, tgl@sss.pgh.pa.us, andres@anarazel.de
Subject: Re: Improve LWLock tranche name visibility across backends
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