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Commit07e9e28

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Add pg_memory_is_all_zeros() in memutils.h
This new function tests if a memory region starting at a given locationfor a defined length is made only of zeroes. This unifies in a singlepath the all-zero checks that were happening in a couple of places ofthe backend code:- For pgstats entries of relation, checkpointer and bgwriter, wheresome "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-zerobuffer pages, applying it to the three pgstats paths mentioned above.Author: Bertrand DrouvotReviewed-by: Peter Eisentraut, Heikki Linnakangas, Peter SmithDiscussion:https://postgr.es/m/ZupUDDyf1hHI4ibn@ip-10-97-1-34.eu-west-3.compute.internal
1 parent49d6c7d commit07e9e28

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5 files changed

+26
-23
lines changed

5 files changed

+26
-23
lines changed

‎src/backend/storage/page/bufpage.c

Lines changed: 1 addition & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -89,10 +89,8 @@ PageIsVerifiedExtended(Page page, BlockNumber blkno, int flags)
8989
{
9090
PageHeaderp= (PageHeader)page;
9191
size_t*pagebytes;
92-
inti;
9392
boolchecksum_failure= false;
9493
boolheader_sane= false;
95-
boolall_zeroes= false;
9694
uint16checksum=0;
9795

9896
/*
@@ -126,18 +124,9 @@ PageIsVerifiedExtended(Page page, BlockNumber blkno, int flags)
126124
}
127125

128126
/* Check all-zeroes case */
129-
all_zeroes= true;
130127
pagebytes= (size_t*)page;
131-
for (i=0;i< (BLCKSZ /sizeof(size_t));i++)
132-
{
133-
if (pagebytes[i]!=0)
134-
{
135-
all_zeroes= false;
136-
break;
137-
}
138-
}
139128

140-
if (all_zeroes)
129+
if (pg_memory_is_all_zeros(pagebytes, (BLCKSZ /sizeof(size_t))))
141130
return true;
142131

143132
/*

‎src/backend/utils/activity/pgstat_bgwriter.c

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -17,6 +17,7 @@
1717

1818
#include"postgres.h"
1919

20+
#include"utils/memutils.h"
2021
#include"utils/pgstat_internal.h"
2122

2223

@@ -30,7 +31,6 @@ void
3031
pgstat_report_bgwriter(void)
3132
{
3233
PgStatShared_BgWriter*stats_shmem=&pgStatLocal.shmem->bgwriter;
33-
staticconstPgStat_BgWriterStatsall_zeroes;
3434

3535
Assert(!pgStatLocal.shmem->is_shutdown);
3636
pgstat_assert_is_up();
@@ -39,7 +39,8 @@ pgstat_report_bgwriter(void)
3939
* This function can be called even if nothing at all has happened. In
4040
* this case, avoid unnecessarily modifying the stats entry.
4141
*/
42-
if (memcmp(&PendingBgWriterStats,&all_zeroes,sizeof(all_zeroes))==0)
42+
if (pg_memory_is_all_zeros(&PendingBgWriterStats,
43+
sizeof(structPgStat_BgWriterStats)))
4344
return;
4445

4546
pgstat_begin_changecount_write(&stats_shmem->changecount);

‎src/backend/utils/activity/pgstat_checkpointer.c

Lines changed: 3 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -17,6 +17,7 @@
1717

1818
#include"postgres.h"
1919

20+
#include"utils/memutils.h"
2021
#include"utils/pgstat_internal.h"
2122

2223

@@ -29,8 +30,6 @@ PgStat_CheckpointerStats PendingCheckpointerStats = {0};
2930
void
3031
pgstat_report_checkpointer(void)
3132
{
32-
/* We assume this initializes to zeroes */
33-
staticconstPgStat_CheckpointerStatsall_zeroes;
3433
PgStatShared_Checkpointer*stats_shmem=&pgStatLocal.shmem->checkpointer;
3534

3635
Assert(!pgStatLocal.shmem->is_shutdown);
@@ -40,8 +39,8 @@ pgstat_report_checkpointer(void)
4039
* This function can be called even if nothing at all has happened. In
4140
* this case, avoid unnecessarily modifying the stats entry.
4241
*/
43-
if (memcmp(&PendingCheckpointerStats,&all_zeroes,
44-
sizeof(all_zeroes))==0)
42+
if (pg_memory_is_all_zeros(&PendingCheckpointerStats,
43+
sizeof(structPgStat_CheckpointerStats)))
4544
return;
4645

4746
pgstat_begin_changecount_write(&stats_shmem->changecount);

‎src/backend/utils/activity/pgstat_relation.c

Lines changed: 2 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -800,7 +800,6 @@ pgstat_twophase_postabort(TransactionId xid, uint16 info,
800800
bool
801801
pgstat_relation_flush_cb(PgStat_EntryRef*entry_ref,boolnowait)
802802
{
803-
staticconstPgStat_TableCountsall_zeroes;
804803
Oiddboid;
805804
PgStat_TableStatus*lstats;/* pending stats entry */
806805
PgStatShared_Relation*shtabstats;
@@ -815,11 +814,9 @@ pgstat_relation_flush_cb(PgStat_EntryRef *entry_ref, bool nowait)
815814
* Ignore entries that didn't accumulate any actual counts, such as
816815
* indexes that were opened by the planner but not used.
817816
*/
818-
if (memcmp(&lstats->counts,&all_zeroes,
819-
sizeof(PgStat_TableCounts))==0)
820-
{
817+
if (pg_memory_is_all_zeros(&lstats->counts,
818+
sizeof(structPgStat_TableCounts)))
821819
return true;
822-
}
823820

824821
if (!pgstat_lock_entry(entry_ref,nowait))
825822
return false;

‎src/include/utils/memutils.h

Lines changed: 17 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -189,4 +189,21 @@ extern MemoryContext BumpContextCreate(MemoryContext parent,
189189
#defineSLAB_DEFAULT_BLOCK_SIZE(8 * 1024)
190190
#defineSLAB_LARGE_BLOCK_SIZE(8 * 1024 * 1024)
191191

192+
/*
193+
* Test if a memory region starting at "ptr" and of size "len" is full of
194+
* zeroes.
195+
*/
196+
staticinlinebool
197+
pg_memory_is_all_zeros(constvoid*ptr,size_tlen)
198+
{
199+
constchar*p= (constchar*)ptr;
200+
201+
for (size_ti=0;i<len;i++)
202+
{
203+
if (p[i]!=0)
204+
return false;
205+
}
206+
return true;
207+
}
208+
192209
#endif/* MEMUTILS_H */

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