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Commit2850896

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Code review for auto-tuned effective_cache_size.
Fix integer overflow issue noted by Magnus Hagander, as well as a bunchof other infelicities in commitee1e566and its unreasonably large number of followups.
1 parentdd515d4 commit2850896

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7 files changed

+77
-67
lines changed

7 files changed

+77
-67
lines changed

‎doc/src/sgml/config.sgml‎

Lines changed: 13 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -2974,17 +2974,9 @@ include 'filename'
29742974
<listitem>
29752975
<para>
29762976
Sets the planner's assumption about the effective size of the
2977-
disk cache that is available to a single query. The default
2978-
setting of -1 selects a size equal to four times the size of <xref
2979-
linkend="guc-shared-buffers">, but not less than the size of one
2980-
shared buffer page, typically <literal>8kB</literal>. This value
2981-
can be set manually if the automatic choice is too large or too
2982-
small.
2983-
</para>
2984-
2985-
<para>
2986-
This value is factored into estimates of the cost of using an index;
2987-
a higher value makes it more likely index scans will be used, a
2977+
disk cache that is available to a single query. This is
2978+
factored into estimates of the cost of using an index; a
2979+
higher value makes it more likely index scans will be used, a
29882980
lower value makes it more likely sequential scans will be
29892981
used. When setting this parameter you should consider both
29902982
<productname>PostgreSQL</productname>'s shared buffers and the
@@ -2996,10 +2988,16 @@ include 'filename'
29962988
memory allocated by <productname>PostgreSQL</productname>, nor
29972989
does it reserve kernel disk cache; it is used only for estimation
29982990
purposes. The system also does not assume data remains in
2999-
the disk cache between queries. The auto-tuning
3000-
selected by the default setting of -1 should give reasonable
3001-
results if this database cluster can utilize most of the memory
3002-
on this server.
2991+
the disk cache between queries.
2992+
</para>
2993+
2994+
<para>
2995+
If <varname>effective_cache_size</> is set to -1, which is the
2996+
default, the value is replaced by an automatically selected value,
2997+
currently four times the size of <xref linkend="guc-shared-buffers">.
2998+
For recommended settings of <varname>shared_buffers</>, this should
2999+
give reasonable results if this database cluster can use most of the
3000+
memory on the server.
30033001
</para>
30043002
</listitem>
30053003
</varlistentry>

‎src/backend/optimizer/path/costsize.c‎

Lines changed: 59 additions & 47 deletions
Original file line numberDiff line numberDiff line change
@@ -71,6 +71,7 @@
7171
#ifdef_MSC_VER
7272
#include<float.h>/* for _isnan */
7373
#endif
74+
#include<limits.h>
7475
#include<math.h>
7576

7677
#include"access/htup_details.h"
@@ -96,13 +97,14 @@
9697

9798
#defineLOG2(x) (log(x) / 0.693147180559945)
9899

100+
99101
doubleseq_page_cost=DEFAULT_SEQ_PAGE_COST;
100102
doublerandom_page_cost=DEFAULT_RANDOM_PAGE_COST;
101103
doublecpu_tuple_cost=DEFAULT_CPU_TUPLE_COST;
102104
doublecpu_index_tuple_cost=DEFAULT_CPU_INDEX_TUPLE_COST;
103105
doublecpu_operator_cost=DEFAULT_CPU_OPERATOR_COST;
104106

105-
inteffective_cache_size=-1;
107+
inteffective_cache_size=-1;/* will get replaced */
106108

107109
Costdisable_cost=1.0e10;
108110

@@ -456,52 +458,6 @@ cost_index(IndexPath *path, PlannerInfo *root, double loop_count)
456458
path->path.total_cost=startup_cost+run_cost;
457459
}
458460

459-
void
460-
set_default_effective_cache_size(void)
461-
{
462-
/*
463-
* If the value of effective_cache_size is -1, use the preferred
464-
* auto-tune value.
465-
*/
466-
if (effective_cache_size==-1)
467-
{
468-
charbuf[32];
469-
470-
snprintf(buf,sizeof(buf),"%d",NBuffers*DEFAULT_EFFECTIVE_CACHE_SIZE_MULTI);
471-
SetConfigOption("effective_cache_size",buf,PGC_POSTMASTER,PGC_S_OVERRIDE);
472-
}
473-
Assert(effective_cache_size>0);
474-
}
475-
476-
/*
477-
* GUC check_hook for effective_cache_size
478-
*/
479-
bool
480-
check_effective_cache_size(int*newval,void**extra,GucSourcesource)
481-
{
482-
/*
483-
* -1 indicates a request for auto-tune.
484-
*/
485-
if (*newval==-1)
486-
{
487-
/*
488-
* If we haven't yet changed the boot_val default of -1, just let it
489-
* be.We'll fix it later.
490-
*/
491-
if (effective_cache_size==-1)
492-
return true;
493-
494-
/* Otherwise, substitute the auto-tune value */
495-
*newval=NBuffers*DEFAULT_EFFECTIVE_CACHE_SIZE_MULTI;
496-
}
497-
498-
/* set minimum? */
499-
if (*newval<1)
500-
*newval=1;
501-
502-
return true;
503-
}
504-
505461
/*
506462
* index_pages_fetched
507463
* Estimate the number of pages actually fetched after accounting for
@@ -4137,3 +4093,59 @@ page_size(double tuples, int width)
41374093
{
41384094
returnceil(relation_byte_size(tuples,width) /BLCKSZ);
41394095
}
4096+
4097+
/*
4098+
* GUC check_hook for effective_cache_size
4099+
*/
4100+
bool
4101+
check_effective_cache_size(int*newval,void**extra,GucSourcesource)
4102+
{
4103+
/*
4104+
* -1 is the documented way of requesting auto-tune, but we also treat
4105+
* zero as meaning that, since we don't consider zero a valid setting.
4106+
*/
4107+
if (*newval <=0)
4108+
{
4109+
/*
4110+
* If we haven't yet changed the initial default of -1, just let it
4111+
* be.We'll fix it later on during GUC initialization, when
4112+
* set_default_effective_cache_size is called.(If we try to do it
4113+
* immediately, we may not be looking at the final value of NBuffers.)
4114+
*/
4115+
if (effective_cache_size==-1)
4116+
return true;
4117+
4118+
/*
4119+
* Otherwise, substitute the auto-tune value, being wary of overflow.
4120+
*/
4121+
if (NBuffers<INT_MAX /4)
4122+
*newval=NBuffers*4;
4123+
else
4124+
*newval=INT_MAX;
4125+
}
4126+
4127+
Assert(*newval>0);
4128+
4129+
return true;
4130+
}
4131+
4132+
/*
4133+
* initialize effective_cache_size at the end of GUC startup
4134+
*/
4135+
void
4136+
set_default_effective_cache_size(void)
4137+
{
4138+
/*
4139+
* If the value of effective_cache_size is still -1 (or zero), replace it
4140+
* with the auto-tune value.
4141+
*/
4142+
if (effective_cache_size <=0)
4143+
{
4144+
/* disable the short-circuit in check_effective_cache_size */
4145+
effective_cache_size=0;
4146+
/* and let check_effective_cache_size() compute the setting */
4147+
SetConfigOption("effective_cache_size","-1",
4148+
PGC_POSTMASTER,PGC_S_OVERRIDE);
4149+
}
4150+
Assert(effective_cache_size>0);
4151+
}

‎src/backend/postmaster/postmaster.c‎

Lines changed: 0 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -118,7 +118,6 @@
118118
#include"utils/builtins.h"
119119
#include"utils/datetime.h"
120120
#include"utils/dynamic_loader.h"
121-
#include"utils/guc.h"
122121
#include"utils/memutils.h"
123122
#include"utils/ps_status.h"
124123
#include"utils/timeout.h"

‎src/backend/utils/misc/guc.c‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -4305,6 +4305,7 @@ SelectConfigFiles(const char *userDoption, const char *progname)
43054305
*/
43064306
pg_timezone_abbrev_initialize();
43074307

4308+
/* Also install the correct value for effective_cache_size */
43084309
set_default_effective_cache_size();
43094310

43104311
/*

‎src/backend/utils/misc/postgresql.conf.sample‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -279,7 +279,7 @@
279279
#cpu_tuple_cost = 0.01# same scale as above
280280
#cpu_index_tuple_cost = 0.005# same scale as above
281281
#cpu_operator_cost = 0.0025# same scale as above
282-
#effective_cache_size = -1
282+
#effective_cache_size = -1# -1 selects auto-tuned default
283283

284284
# - Genetic Query Optimizer -
285285

‎src/include/optimizer/cost.h‎

Lines changed: 0 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -27,8 +27,6 @@
2727
#defineDEFAULT_CPU_INDEX_TUPLE_COST 0.005
2828
#defineDEFAULT_CPU_OPERATOR_COST 0.0025
2929

30-
#defineDEFAULT_EFFECTIVE_CACHE_SIZE_MULTI 4
31-
3230
typedefenum
3331
{
3432
CONSTRAINT_EXCLUSION_OFF,/* do not use c_e */

‎src/include/utils/guc.h‎

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -387,8 +387,10 @@ extern void assign_search_path(const char *newval, void *extra);
387387

388388
/* in access/transam/xlog.c */
389389
externboolcheck_wal_buffers(int*newval,void**extra,GucSourcesource);
390+
externvoidassign_xlog_sync_method(intnew_sync_method,void*extra);
391+
392+
/* in optimizer/path/costsize.c */
390393
externboolcheck_effective_cache_size(int*newval,void**extra,GucSourcesource);
391394
externvoidset_default_effective_cache_size(void);
392-
externvoidassign_xlog_sync_method(intnew_sync_method,void*extra);
393395

394396
#endif/* GUC_H */

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