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Add pg_memory_is_all_zeros() in memutils.h

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This new function tests if a memory region starting at a given location
for a defined length is made only of zeroes.  This unifies in a single
path the all-zero checks that were happening in a couple of places of
the backend code:
- For pgstats entries of relation, checkpointer and bgwriter, where
some "all_zeroes" variables were previously used with memcpy().
- For all-zero buffer pages in PageIsVerifiedExtended().

This new function uses the same forward scan as the check for all-zero
buffer pages, applying it to the three pgstats paths mentioned above.

Author: Bertrand Drouvot
Reviewed-by: Peter Eisentraut, Heikki Linnakangas, Peter Smith
Discussion: https://postgr.es/m/ZupUDDyf1hHI4ibn@ip-10-97-1-34.eu-west-3.compute.internal
This commit is contained in:
Michael Paquier
2024-11-01 11:35:46 +09:00
parent 49d6c7d8da
commit 07e9e28b56
5 changed files with 26 additions and 23 deletions
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5
src/backend/utils/activity/pgstat_bgwriter.c
View File

@@ -17,6 +17,7 @@
#include "postgres.h"
#include "utils/memutils.h"
#include "utils/pgstat_internal.h"
@@ -30,7 +31,6 @@ void
pgstat_report_bgwriter(void)
{
PgStatShared_BgWriter *stats_shmem = &pgStatLocal.shmem->bgwriter;
static const PgStat_BgWriterStats all_zeroes;
Assert(!pgStatLocal.shmem->is_shutdown);
pgstat_assert_is_up();
@@ -39,7 +39,8 @@ pgstat_report_bgwriter(void)
* This function can be called even if nothing at all has happened. In
* this case, avoid unnecessarily modifying the stats entry.
*/
if (memcmp(&PendingBgWriterStats, &all_zeroes, sizeof(all_zeroes)) == 0)
if (pg_memory_is_all_zeros(&PendingBgWriterStats,
sizeof(struct PgStat_BgWriterStats)))
return;
pgstat_begin_changecount_write(&stats_shmem->changecount);

7
src/backend/utils/activity/pgstat_checkpointer.c
View File

@@ -17,6 +17,7 @@
#include "postgres.h"
#include "utils/memutils.h"
#include "utils/pgstat_internal.h"
@@ -29,8 +30,6 @@ PgStat_CheckpointerStats PendingCheckpointerStats = {0};
void
pgstat_report_checkpointer(void)
{
/* We assume this initializes to zeroes */
static const PgStat_CheckpointerStats all_zeroes;
PgStatShared_Checkpointer *stats_shmem = &pgStatLocal.shmem->checkpointer;
Assert(!pgStatLocal.shmem->is_shutdown);
@@ -40,8 +39,8 @@ pgstat_report_checkpointer(void)
* This function can be called even if nothing at all has happened. In
* this case, avoid unnecessarily modifying the stats entry.
*/
if (memcmp(&PendingCheckpointerStats, &all_zeroes,
sizeof(all_zeroes)) == 0)
if (pg_memory_is_all_zeros(&PendingCheckpointerStats,
sizeof(struct PgStat_CheckpointerStats)))
return;
pgstat_begin_changecount_write(&stats_shmem->changecount);

7
src/backend/utils/activity/pgstat_relation.c
View File

@@ -800,7 +800,6 @@ pgstat_twophase_postabort(TransactionId xid, uint16 info,
bool
pgstat_relation_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
{
static const PgStat_TableCounts all_zeroes;
Oid dboid;
PgStat_TableStatus *lstats; /* pending stats entry */
PgStatShared_Relation *shtabstats;
@@ -815,11 +814,9 @@ pgstat_relation_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
* Ignore entries that didn't accumulate any actual counts, such as
* indexes that were opened by the planner but not used.
*/
if (memcmp(&lstats->counts, &all_zeroes,
sizeof(PgStat_TableCounts)) == 0)
{
if (pg_memory_is_all_zeros(&lstats->counts,
sizeof(struct PgStat_TableCounts)))
return true;
}
if (!pgstat_lock_entry(entry_ref, nowait))
return false;