Xlogprefetcher: Use atomic add for increment counter
Hi.
Use pg_atomic_fetch_add_u64 to replace pg_atomic_read_u64 and
pg_atomic_write_u64 calls.
This simplifies the logic and this increases the likelihood that the
operation will be successful.
patch attached.
best regards,
Ranier Vilela
Attachments:
use-atomic-add-for-increment-counter.patchapplication/octet-stream; name=use-atomic-add-for-increment-counter.patchDownload
diff --git a/src/backend/access/transam/xlogprefetcher.c b/src/backend/access/transam/xlogprefetcher.c
index ed3aacabc9..3dbd4925bd 100644
--- a/src/backend/access/transam/xlogprefetcher.c
+++ b/src/backend/access/transam/xlogprefetcher.c
@@ -351,7 +351,7 @@ static inline void
XLogPrefetchIncrement(pg_atomic_uint64 *counter)
{
Assert(AmStartupProcess() || !IsUnderPostmaster);
- pg_atomic_write_u64(counter, pg_atomic_read_u64(counter) + 1);
+ pg_atomic_fetch_add_u64(counter, 1);
}
/*
Hi,
On 2025-11-07 11:28:06 -0300, Ranier Vilela wrote:
Use pg_atomic_fetch_add_u64 to replace pg_atomic_read_u64 and
pg_atomic_write_u64 calls.This simplifies the logic and this increases the likelihood that the
operation will be successful.
How does it do so? As the assertions indicate, this can only be run from a
single process.
Greetings,
Andres Freund
Em sex., 7 de nov. de 2025 às 11:41, Andres Freund <andres@anarazel.de>
escreveu:
Hi,
On 2025-11-07 11:28:06 -0300, Ranier Vilela wrote:
Use pg_atomic_fetch_add_u64 to replace pg_atomic_read_u64 and
pg_atomic_write_u64 calls.This simplifies the logic and this increases the likelihood that the
operation will be successful.How does it do so? As the assertions indicate, this can only be run from a
single process.
Can I rephrase that?
That simplifies the logic a bit.
best regards,
Ranier Vilela
On 2025-11-07 11:52:37 -0300, Ranier Vilela wrote:
Em sex., 7 de nov. de 2025 �s 11:41, Andres Freund <andres@anarazel.de>
escreveu:On 2025-11-07 11:28:06 -0300, Ranier Vilela wrote:
Use pg_atomic_fetch_add_u64 to replace pg_atomic_read_u64 and
pg_atomic_write_u64 calls.This simplifies the logic and this increases the likelihood that the
operation will be successful.How does it do so? As the assertions indicate, this can only be run from a
single process.Can I rephrase that?
That simplifies the logic a bit.
Maybe simpler, but also vastly slower than before. An atomic increment is
maybe two orders of magnitude more expensive than an unlocked read & write.
Em sex., 7 de nov. de 2025 às 11:59, Andres Freund <andres@anarazel.de>
escreveu:
On 2025-11-07 11:52:37 -0300, Ranier Vilela wrote:
Em sex., 7 de nov. de 2025 às 11:41, Andres Freund <andres@anarazel.de>
escreveu:On 2025-11-07 11:28:06 -0300, Ranier Vilela wrote:
Use pg_atomic_fetch_add_u64 to replace pg_atomic_read_u64 and
pg_atomic_write_u64 calls.This simplifies the logic and this increases the likelihood that the
operation will be successful.How does it do so? As the assertions indicate, this can only be run
from a
single process.
Can I rephrase that?
That simplifies the logic a bit.
Maybe simpler, but also vastly slower than before. An atomic increment is
maybe two orders of magnitude more expensive than an unlocked read & write.
Seriously, I didn't know.
It's best to withdraw the patch then.
Thanks for clarifying this.
best regards,
Ranier Vilela