Обсуждение: Wal_keep_size
Should Wal_keep_size <= max_wal_size ?
Hope nobody minds me chipping in here.
The answer is "not necessarily." The names make them seem closely related, but not so much.
max_wal_size is all about checkpoints. When the WAL exceeds this, Postgres will try to run a checkpoint. Under some circumstances it won't, but let's keep it simple for now.
wal_keep_size is all about replication. Replicas need WAL files to stick around for long enough that they can process them. wal_keep_size is a minimum figure.
Tom
On Monday, October 6, 2025 at 03:51:17 PM EDT, Raj <rajeshkumar.dba09@gmail.com> wrote:
Should Wal_keep_size <= max_wal_size ?
If wal_keep_size is more than max_wal_size wouldn't it always trigger checkpoint ?
On Tue, 7 Oct 2025, 03:08 Thomas Carroll, <tomfecarroll@yahoo.com> wrote:
Hope nobody minds me chipping in here.The answer is "not necessarily." The names make them seem closely related, but not so much.max_wal_size is all about checkpoints. When the WAL exceeds this, Postgres will try to run a checkpoint. Under some circumstances it won't, but let's keep it simple for now.wal_keep_size is all about replication. Replicas need WAL files to stick around for long enough that they can process them. wal_keep_size is a minimum figure.TomOn Monday, October 6, 2025 at 03:51:17 PM EDT, Raj <rajeshkumar.dba09@gmail.com> wrote:Should Wal_keep_size <= max_wal_size ?
Note archive mode is enabled.
On Tue, 7 Oct 2025, 10:22 Raj, <rajeshkumar.dba09@gmail.com> wrote:
If wal_keep_size is more than max_wal_size wouldn't it always trigger checkpoint ?On Tue, 7 Oct 2025, 03:08 Thomas Carroll, <tomfecarroll@yahoo.com> wrote:Hope nobody minds me chipping in here.The answer is "not necessarily." The names make them seem closely related, but not so much.max_wal_size is all about checkpoints. When the WAL exceeds this, Postgres will try to run a checkpoint. Under some circumstances it won't, but let's keep it simple for now.wal_keep_size is all about replication. Replicas need WAL files to stick around for long enough that they can process them. wal_keep_size is a minimum figure.TomOn Monday, October 6, 2025 at 03:51:17 PM EDT, Raj <rajeshkumar.dba09@gmail.com> wrote:Should Wal_keep_size <= max_wal_size ?
On Tue, 2025-10-07 at 10:22 +0530, Raj wrote: > If wal_keep_size is more than max_wal_size wouldn't it always trigger checkpoint ? No. "max_wal_size" has no direct connection with the size of WAL (and I think we should have chosen a different name for that parameter). The parameter is about the amount of WAL *generated since the latest checkpoint*, not about the absolute amount of WAL present. Yours, Laurenz Albe