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Add writeback to pg_stat_io

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28e626bde0 added the concept of IOOps but neglected to include writeback
operations. ac8d53dae5 added time spent doing these I/O operations. Without
counting writeback, checkpointer write time in the log often differed
substantially from that in pg_stat_io. To fix this, add IOOp IOOP_WRITEBACK
and track writeback in pg_stat_io.

Bumps catversion.

Author: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reported-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20230419172326.dhgyo4wrrhulovt6%40awork3.anarazel.de
This commit is contained in:
Andres Freund
2023-05-17 11:18:35 -07:00
parent 52676dc2e0
commit 093e5c57d5
12 changed files with 82 additions and 25 deletions
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32
src/backend/storage/buffer/bufmgr.c
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@ -1685,7 +1685,7 @@ again:
FlushBuffer(buf_hdr, NULL, IOOBJECT_RELATION, io_context);
LWLockRelease(content_lock);
ScheduleBufferTagForWriteback(&BackendWritebackContext,
ScheduleBufferTagForWriteback(&BackendWritebackContext, io_context,
&buf_hdr->tag);
}
@ -2725,8 +2725,11 @@ BufferSync(int flags)
CheckpointWriteDelay(flags, (double) num_processed / num_to_scan);
}
/* issue all pending flushes */
IssuePendingWritebacks(&wb_context);
/*
* Issue all pending flushes. Only checkpointer calls BufferSync(), so
* IOContext will always be IOCONTEXT_NORMAL.
*/
IssuePendingWritebacks(&wb_context, IOCONTEXT_NORMAL);
pfree(per_ts_stat);
per_ts_stat = NULL;
@ -3110,7 +3113,11 @@ SyncOneBuffer(int buf_id, bool skip_recently_used, WritebackContext *wb_context)
UnpinBuffer(bufHdr);
ScheduleBufferTagForWriteback(wb_context, &tag);
/*
* SyncOneBuffer() is only called by checkpointer and bgwriter, so
* IOContext will always be IOCONTEXT_NORMAL.
*/
ScheduleBufferTagForWriteback(wb_context, IOCONTEXT_NORMAL, &tag);
return result | BUF_WRITTEN;
}
@ -5445,7 +5452,8 @@ WritebackContextInit(WritebackContext *context, int *max_pending)
* Add buffer to list of pending writeback requests.
*/
void
ScheduleBufferTagForWriteback(WritebackContext *wb_context, BufferTag *tag)
ScheduleBufferTagForWriteback(WritebackContext *wb_context, IOContext io_context,
BufferTag *tag)
{
PendingWriteback *pending;
@ -5471,7 +5479,7 @@ ScheduleBufferTagForWriteback(WritebackContext *wb_context, BufferTag *tag)
* is now disabled.
*/
if (wb_context->nr_pending >= *wb_context->max_pending)
IssuePendingWritebacks(wb_context);
IssuePendingWritebacks(wb_context, io_context);
}
#define ST_SORT sort_pending_writebacks
@ -5489,8 +5497,9 @@ ScheduleBufferTagForWriteback(WritebackContext *wb_context, BufferTag *tag)
* error out - it's just a hint.
*/
void
IssuePendingWritebacks(WritebackContext *wb_context)
IssuePendingWritebacks(WritebackContext *wb_context, IOContext io_context)
{
instr_time io_start;
int i;
if (wb_context->nr_pending == 0)
@ -5503,6 +5512,8 @@ IssuePendingWritebacks(WritebackContext *wb_context)
sort_pending_writebacks(wb_context->pending_writebacks,
wb_context->nr_pending);
io_start = pgstat_prepare_io_time();
/*
* Coalesce neighbouring writes, but nothing else. For that we iterate
* through the, now sorted, array of pending flushes, and look forward to
@ -5556,6 +5567,13 @@ IssuePendingWritebacks(WritebackContext *wb_context)
smgrwriteback(reln, BufTagGetForkNum(&tag), tag.blockNum, nblocks);
}
/*
* Assume that writeback requests are only issued for buffers containing
* blocks of permanent relations.
*/
pgstat_count_io_op_time(IOOBJECT_RELATION, io_context,
IOOP_WRITEBACK, io_start, wb_context->nr_pending);
wb_context->nr_pending = 0;
}