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Remove buffers_backend and buffers_backend_fsync from pg_stat_checkpointer

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Two attributes related to checkpointer statistics are removed in this
commit:
- buffers_backend, that counts the number of buffers written directly by
a backend.
- buffers_backend_fsync, that counts the number of times a backend had
to do fsync() by its own.

These are actually not checkpointer properties but backend properties.
Also, pg_stat_io provides a more accurate and equivalent report of these
numbers, by tracking all the I/O stats related to backends, including
writes and fsyncs, so storing them in pg_stat_checkpointer was
redundant.

Thanks also to Robert Haas and Amit Kapila for their input.

Bump catalog version.

Author: Bharath Rupireddy
Reviewed-by: Bertrand Drouvot, Andres Freund
Discussion: https://postgr.es/m/20230210004604.mcszbscsqs3bc5nx@awork3.anarazel.de
This commit is contained in:
Michael Paquier
2023-10-27 11:16:39 +09:00
parent 0c882a2988
commit 74604a37f2
9 changed files with 3 additions and 82 deletions
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32
src/backend/postmaster/checkpointer.c
View File

@ -91,17 +91,11 @@
* requesting backends since the last checkpoint start. The flags are
* chosen so that OR'ing is the correct way to combine multiple requests.
*
* num_backend_writes is used to count the number of buffer writes performed
* by user backend processes. This counter should be wide enough that it
* can't overflow during a single processing cycle. num_backend_fsync
* counts the subset of those writes that also had to do their own fsync,
* because the checkpointer failed to absorb their request.
*
* The requests array holds fsync requests sent by backends and not yet
* absorbed by the checkpointer.
*
* Unlike the checkpoint fields, num_backend_writes, num_backend_fsync, and
* the requests fields are protected by CheckpointerCommLock.
* Unlike the checkpoint fields, requests related fields are protected by
* CheckpointerCommLock.
*----------
*/
typedef struct
@ -125,9 +119,6 @@ typedef struct
ConditionVariable start_cv; /* signaled when ckpt_started advances */
ConditionVariable done_cv; /* signaled when ckpt_done advances */
uint32 num_backend_writes; /* counts user backend buffer writes */
uint32 num_backend_fsync; /* counts user backend fsync calls */
int num_requests; /* current # of requests */
int max_requests; /* allocated array size */
CheckpointerRequest requests[FLEXIBLE_ARRAY_MEMBER];
@ -1095,10 +1086,6 @@ ForwardSyncRequest(const FileTag *ftag, SyncRequestType type)
LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
/* Count all backend writes regardless of if they fit in the queue */
if (!AmBackgroundWriterProcess())
CheckpointerShmem->num_backend_writes++;
/*
* If the checkpointer isn't running or the request queue is full, the
* backend will have to perform its own fsync request. But before forcing
@ -1108,12 +1095,6 @@ ForwardSyncRequest(const FileTag *ftag, SyncRequestType type)
(CheckpointerShmem->num_requests >= CheckpointerShmem->max_requests &&
!CompactCheckpointerRequestQueue()))
{
/*
* Count the subset of writes where backends have to do their own
* fsync
*/
if (!AmBackgroundWriterProcess())
CheckpointerShmem->num_backend_fsync++;
LWLockRelease(CheckpointerCommLock);
return false;
}
@ -1270,15 +1251,6 @@ AbsorbSyncRequests(void)
LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
/* Transfer stats counts into pending pgstats message */
PendingCheckpointerStats.buf_written_backend
+= CheckpointerShmem->num_backend_writes;
PendingCheckpointerStats.buf_fsync_backend
+= CheckpointerShmem->num_backend_fsync;
CheckpointerShmem->num_backend_writes = 0;
CheckpointerShmem->num_backend_fsync = 0;
/*
* We try to avoid holding the lock for a long time by copying the request
* array, and processing the requests after releasing the lock.