database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-27 12:41:57 +03:00
Code Activity

pg_buffercache: Add pg_buffercache_summary()

Browse Source 
Using pg_buffercache_summary() is significantly cheaper than querying
pg_buffercache and summarizing in SQL.

Author: Melih Mutlu <m.melihmutlu@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Aleksander Alekseev <aleksander@timescale.com>
Reviewed-by: Zhang Mingli <zmlpostgres@gmail.com>
Discussion: https://postgr.es/m/CAGPVpCQAXYo54Q%3D8gqBsS%3Du0uk9qhnnq4%2B710BtUhUisX1XGEg%40mail.gmail.com
This commit is contained in:
Andres Freund
2022-10-13 09:55:46 -07:00
parent 7f8d9cedb3
commit 2589434ae0
8 changed files with 250 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

67
contrib/pg_buffercache/pg_buffercache_pages.c
View File

@ -17,6 +17,7 @@
#define NUM_BUFFERCACHE_PAGES_MIN_ELEM 8
#define NUM_BUFFERCACHE_PAGES_ELEM 9
#define NUM_BUFFERCACHE_SUMMARY_ELEM 5
PG_MODULE_MAGIC;
@ -59,6 +60,7 @@ typedef struct
* relation node/tablespace/database/blocknum and dirty indicator.
*/
PG_FUNCTION_INFO_V1(pg_buffercache_pages);
PG_FUNCTION_INFO_V1(pg_buffercache_summary);
Datum
pg_buffercache_pages(PG_FUNCTION_ARGS)
@ -237,3 +239,68 @@ pg_buffercache_pages(PG_FUNCTION_ARGS)
else
SRF_RETURN_DONE(funcctx);
}
Datum
pg_buffercache_summary(PG_FUNCTION_ARGS)
{
Datum result;
TupleDesc tupledesc;
HeapTuple tuple;
Datum values[NUM_BUFFERCACHE_SUMMARY_ELEM];
bool nulls[NUM_BUFFERCACHE_SUMMARY_ELEM];
int32 buffers_used = 0;
int32 buffers_unused = 0;
int32 buffers_dirty = 0;
int32 buffers_pinned = 0;
int64 usagecount_total = 0;
if (get_call_result_type(fcinfo, NULL, &tupledesc) != TYPEFUNC_COMPOSITE)
elog(ERROR, "return type must be a row type");
for (int i = 0; i < NBuffers; i++)
{
BufferDesc *bufHdr;
uint32 buf_state;
/*
* This function summarizes the state of all headers. Locking the
* buffer headers wouldn't provide an improved result as the state of
* the buffer can still change after we release the lock and it'd
* noticeably increase the cost of the function.
*/
bufHdr = GetBufferDescriptor(i);
buf_state = pg_atomic_read_u32(&bufHdr->state);
if (buf_state & BM_VALID)
{
buffers_used++;
usagecount_total += BUF_STATE_GET_USAGECOUNT(buf_state);
if (buf_state & BM_DIRTY)
buffers_dirty++;
}
else
buffers_unused++;
if (BUF_STATE_GET_REFCOUNT(buf_state) > 0)
buffers_pinned++;
}
memset(nulls, 0, sizeof(nulls));
values[0] = Int32GetDatum(buffers_used);
values[1] = Int32GetDatum(buffers_unused);
values[2] = Int32GetDatum(buffers_dirty);
values[3] = Int32GetDatum(buffers_pinned);
if (buffers_used != 0)
values[4] = Float8GetDatum((double) usagecount_total / buffers_used);
else
nulls[4] = true;
/* Build and return the tuple. */
tuple = heap_form_tuple(tupledesc, values, nulls);
result = HeapTupleGetDatum(tuple);
PG_RETURN_DATUM(result);
}