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Commit1aba62e

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Allow per-tablespace effective_io_concurrency
Per discussion, nowadays it is possible to have tablespaces that havewildly different I/O characteristics from others. Setting differenteffective_io_concurrency parameters for those has been measured toimprove performance.Author: Julien RouhaudReviewed by: Andres Freund
1 parent665a00c commit1aba62e

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12 files changed

+145
-63
lines changed

12 files changed

+145
-63
lines changed

‎doc/src/sgml/config.sgml‎

Lines changed: 4 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1901,7 +1901,10 @@ include_dir 'conf.d'
19011901
</para>
19021902

19031903
<para>
1904-
The default is 1 on supported systems, otherwise 0.
1904+
The default is 1 on supported systems, otherwise 0. This value can
1905+
be overriden for tables in a particular tablespace by setting the
1906+
tablespace parameter of the same name (see
1907+
<xref linkend="sql-altertablespace">).
19051908
</para>
19061909
</listitem>
19071910
</varlistentry>

‎doc/src/sgml/ref/create_tablespace.sgml‎

Lines changed: 9 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -104,14 +104,15 @@ CREATE TABLESPACE <replaceable class="parameter">tablespace_name</replaceable>
104104
<listitem>
105105
<para>
106106
A tablespace parameter to be set or reset. Currently, the only
107-
available parameters are <varname>seq_page_cost</> and
108-
<varname>random_page_cost</>. Setting either value for a particular
109-
tablespace will override the planner's usual estimate of the cost of
110-
reading pages from tables in that tablespace, as established by
111-
the configuration parameters of the same name (see
112-
<xref linkend="guc-seq-page-cost">,
113-
<xref linkend="guc-random-page-cost">). This may be useful if one
114-
tablespace is located on a disk which is faster or slower than the
107+
available parameters are <varname>seq_page_cost</>,
108+
<varname>random_page_cost</> and <varname>effective_io_concurrency</>.
109+
Setting either value for a particular tablespace will override the
110+
planner's usual estimate of the cost of reading pages from tables in
111+
that tablespace, as established by the configuration parameters of the
112+
same name (see <xref linkend="guc-seq-page-cost">,
113+
<xref linkend="guc-random-page-cost">,
114+
<xref linkend="guc-effective-io-concurrency">). This may be useful if
115+
one tablespace is located on a disk which is faster or slower than the
115116
remainder of the I/O subsystem.
116117
</para>
117118
</listitem>

‎src/backend/access/common/reloptions.c‎

Lines changed: 15 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -254,6 +254,19 @@ static relopt_int intRelOpts[] =
254254
},
255255
-1,64,MAX_KILOBYTES
256256
},
257+
{
258+
{
259+
"effective_io_concurrency",
260+
"Number of simultaneous requests that can be handled efficiently by the disk subsystem.",
261+
RELOPT_KIND_TABLESPACE,
262+
AccessExclusiveLock
263+
},
264+
#ifdefUSE_PREFETCH
265+
-1,0,MAX_IO_CONCURRENCY
266+
#else
267+
0,0,0
268+
#endif
269+
},
257270

258271
/* list terminator */
259272
{{NULL}}
@@ -1438,7 +1451,8 @@ tablespace_reloptions(Datum reloptions, bool validate)
14381451
intnumoptions;
14391452
staticconstrelopt_parse_elttab[]= {
14401453
{"random_page_cost",RELOPT_TYPE_REAL, offsetof(TableSpaceOpts,random_page_cost)},
1441-
{"seq_page_cost",RELOPT_TYPE_REAL, offsetof(TableSpaceOpts,seq_page_cost)}
1454+
{"seq_page_cost",RELOPT_TYPE_REAL, offsetof(TableSpaceOpts,seq_page_cost)},
1455+
{"effective_io_concurrency",RELOPT_TYPE_INT, offsetof(TableSpaceOpts,effective_io_concurrency)}
14421456
};
14431457

14441458
options=parseRelOptions(reloptions,validate,RELOPT_KIND_TABLESPACE,

‎src/backend/executor/nodeBitmapHeapscan.c‎

Lines changed: 27 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -44,6 +44,7 @@
4444
#include"storage/predicate.h"
4545
#include"utils/memutils.h"
4646
#include"utils/rel.h"
47+
#include"utils/spccache.h"
4748
#include"utils/snapmgr.h"
4849
#include"utils/tqual.h"
4950

@@ -95,9 +96,8 @@ BitmapHeapNext(BitmapHeapScanState *node)
9596
* prefetching. node->prefetch_pages tracks exactly how many pages ahead
9697
* the prefetch iterator is. Also, node->prefetch_target tracks the
9798
* desired prefetch distance, which starts small and increases up to the
98-
* GUC-controlled maximum, target_prefetch_pages. This is to avoid doing
99-
* a lot of prefetching in a scan that stops after a few tuples because of
100-
* a LIMIT.
99+
* node->prefetch_maximum. This is to avoid doing a lot of prefetching in
100+
* a scan that stops after a few tuples because of a LIMIT.
101101
*/
102102
if (tbm==NULL)
103103
{
@@ -111,7 +111,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
111111
node->tbmres=tbmres=NULL;
112112

113113
#ifdefUSE_PREFETCH
114-
if (target_prefetch_pages>0)
114+
if (node->prefetch_maximum>0)
115115
{
116116
node->prefetch_iterator=prefetch_iterator=tbm_begin_iterate(tbm);
117117
node->prefetch_pages=0;
@@ -188,10 +188,10 @@ BitmapHeapNext(BitmapHeapScanState *node)
188188
* page/tuple, then to one after the second tuple is fetched, then
189189
* it doubles as later pages are fetched.
190190
*/
191-
if (node->prefetch_target >=target_prefetch_pages)
191+
if (node->prefetch_target >=node->prefetch_maximum)
192192
/* don't increase any further */ ;
193-
elseif (node->prefetch_target >=target_prefetch_pages /2)
194-
node->prefetch_target=target_prefetch_pages;
193+
elseif (node->prefetch_target >=node->prefetch_maximum /2)
194+
node->prefetch_target=node->prefetch_maximum;
195195
elseif (node->prefetch_target>0)
196196
node->prefetch_target *=2;
197197
else
@@ -211,7 +211,7 @@ BitmapHeapNext(BitmapHeapScanState *node)
211211
* Try to prefetch at least a few pages even before we get to the
212212
* second page if we don't stop reading after the first tuple.
213213
*/
214-
if (node->prefetch_target<target_prefetch_pages)
214+
if (node->prefetch_target<node->prefetch_maximum)
215215
node->prefetch_target++;
216216
#endif/* USE_PREFETCH */
217217
}
@@ -539,6 +539,7 @@ ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate, int eflags)
539539
{
540540
BitmapHeapScanState*scanstate;
541541
RelationcurrentRelation;
542+
intio_concurrency;
542543

543544
/* check for unsupported flags */
544545
Assert(!(eflags& (EXEC_FLAG_BACKWARD |EXEC_FLAG_MARK)));
@@ -564,6 +565,8 @@ ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate, int eflags)
564565
scanstate->prefetch_iterator=NULL;
565566
scanstate->prefetch_pages=0;
566567
scanstate->prefetch_target=0;
568+
/* may be updated below */
569+
scanstate->prefetch_maximum=target_prefetch_pages;
567570

568571
/*
569572
* Miscellaneous initialization
@@ -598,6 +601,22 @@ ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate, int eflags)
598601
*/
599602
currentRelation=ExecOpenScanRelation(estate,node->scan.scanrelid,eflags);
600603

604+
/*
605+
* Determine the maximum for prefetch_target. If the tablespace has a
606+
* specific IO concurrency set, use that to compute the corresponding
607+
* maximum value; otherwise, we already initialized to the value computed
608+
* by the GUC machinery.
609+
*/
610+
io_concurrency=
611+
get_tablespace_io_concurrency(currentRelation->rd_rel->reltablespace);
612+
if (io_concurrency!=effective_io_concurrency)
613+
{
614+
doublemaximum;
615+
616+
if (ComputeIoConcurrency(io_concurrency,&maximum))
617+
scanstate->prefetch_maximum=rint(maximum);
618+
}
619+
601620
scanstate->ss.ss_currentRelation=currentRelation;
602621

603622
/*

‎src/backend/storage/buffer/bufmgr.c‎

Lines changed: 62 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -80,11 +80,14 @@ boolzero_damaged_pages = false;
8080
intbgwriter_lru_maxpages=100;
8181
doublebgwriter_lru_multiplier=2.0;
8282
booltrack_io_timing= false;
83+
inteffective_io_concurrency=0;
8384

8485
/*
8586
* How many buffers PrefetchBuffer callers should try to stay ahead of their
8687
* ReadBuffer calls by. This is maintained by the assign hook for
87-
* effective_io_concurrency. Zero means "never prefetch".
88+
* effective_io_concurrency. Zero means "never prefetch". This value is
89+
* only used for buffers not belonging to tablespaces that have their
90+
* effective_io_concurrency parameter set.
8891
*/
8992
inttarget_prefetch_pages=0;
9093

@@ -415,6 +418,64 @@ static void CheckForBufferLeaks(void);
415418
staticintrnode_comparator(constvoid*p1,constvoid*p2);
416419

417420

421+
/*
422+
* ComputeIoConcurrency -- get the number of pages to prefetch for a given
423+
*number of spindles.
424+
*/
425+
bool
426+
ComputeIoConcurrency(intio_concurrency,double*target)
427+
{
428+
doublenew_prefetch_pages=0.0;
429+
inti;
430+
431+
/*
432+
* Make sure the io_concurrency value is within valid range; it may have
433+
* been forced with a manual pg_tablespace update.
434+
*/
435+
io_concurrency=Min(Max(io_concurrency,0),MAX_IO_CONCURRENCY);
436+
437+
/*----------
438+
* The user-visible GUC parameter is the number of drives (spindles),
439+
* which we need to translate to a number-of-pages-to-prefetch target.
440+
* The target value is stashed in *extra and then assigned to the actual
441+
* variable by assign_effective_io_concurrency.
442+
*
443+
* The expected number of prefetch pages needed to keep N drives busy is:
444+
*
445+
* drives | I/O requests
446+
* -------+----------------
447+
*1 | 1
448+
*2 | 2/1 + 2/2 = 3
449+
*3 | 3/1 + 3/2 + 3/3 = 5 1/2
450+
*4 | 4/1 + 4/2 + 4/3 + 4/4 = 8 1/3
451+
*n | n * H(n)
452+
*
453+
* This is called the "coupon collector problem" and H(n) is called the
454+
* harmonic series. This could be approximated by n * ln(n), but for
455+
* reasonable numbers of drives we might as well just compute the series.
456+
*
457+
* Alternatively we could set the target to the number of pages necessary
458+
* so that the expected number of active spindles is some arbitrary
459+
* percentage of the total. This sounds the same but is actually slightly
460+
* different. The result ends up being ln(1-P)/ln((n-1)/n) where P is
461+
* that desired fraction.
462+
*
463+
* Experimental results show that both of these formulas aren't aggressive
464+
* enough, but we don't really have any better proposals.
465+
*
466+
* Note that if io_concurrency = 0 (disabled), we must set target = 0.
467+
*----------
468+
*/
469+
470+
for (i=1;i <=io_concurrency;i++)
471+
new_prefetch_pages+= (double)io_concurrency / (double)i;
472+
473+
*target=new_prefetch_pages;
474+
475+
/* This range check shouldn't fail, but let's be paranoid */
476+
return (new_prefetch_pages>0.0&&new_prefetch_pages< (double)INT_MAX);
477+
}
478+
418479
/*
419480
* PrefetchBuffer -- initiate asynchronous read of a block of a relation
420481
*

‎src/backend/utils/cache/spccache.c‎

Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -23,6 +23,7 @@
2323
#include"commands/tablespace.h"
2424
#include"miscadmin.h"
2525
#include"optimizer/cost.h"
26+
#include"storage/bufmgr.h"
2627
#include"utils/catcache.h"
2728
#include"utils/hsearch.h"
2829
#include"utils/inval.h"
@@ -198,3 +199,14 @@ get_tablespace_page_costs(Oid spcid,
198199
*spc_seq_page_cost=spc->opts->seq_page_cost;
199200
}
200201
}
202+
203+
int
204+
get_tablespace_io_concurrency(Oidspcid)
205+
{
206+
TableSpaceCacheEntry*spc=get_tablespace(spcid);
207+
208+
if (!spc->opts||spc->opts->effective_io_concurrency<0)
209+
returneffective_io_concurrency;
210+
else
211+
returnspc->opts->effective_io_concurrency;
212+
}

‎src/backend/utils/misc/guc.c‎

Lines changed: 3 additions & 42 deletions
Original file line numberDiff line numberDiff line change
@@ -490,7 +490,6 @@ static intwal_block_size;
490490
staticbooldata_checksums;
491491
staticintwal_segment_size;
492492
staticboolinteger_datetimes;
493-
staticinteffective_io_concurrency;
494493
staticboolassert_enabled;
495494

496495
/* should be static, but commands/variable.c needs to get at this */
@@ -2352,7 +2351,7 @@ static struct config_int ConfigureNamesInt[] =
23522351
},
23532352
&effective_io_concurrency,
23542353
#ifdefUSE_PREFETCH
2355-
1,0,1000,
2354+
1,0,MAX_IO_CONCURRENCY,
23562355
#else
23572356
0,0,0,
23582357
#endif
@@ -9986,47 +9985,9 @@ static bool
99869985
check_effective_io_concurrency(int*newval,void**extra,GucSourcesource)
99879986
{
99889987
#ifdefUSE_PREFETCH
9989-
doublenew_prefetch_pages=0.0;
9990-
inti;
9991-
9992-
/*----------
9993-
* The user-visible GUC parameter is the number of drives (spindles),
9994-
* which we need to translate to a number-of-pages-to-prefetch target.
9995-
* The target value is stashed in *extra and then assigned to the actual
9996-
* variable by assign_effective_io_concurrency.
9997-
*
9998-
* The expected number of prefetch pages needed to keep N drives busy is:
9999-
*
10000-
* drives | I/O requests
10001-
* -------+----------------
10002-
*1 | 1
10003-
*2 | 2/1 + 2/2 = 3
10004-
*3 | 3/1 + 3/2 + 3/3 = 5 1/2
10005-
*4 | 4/1 + 4/2 + 4/3 + 4/4 = 8 1/3
10006-
*n | n * H(n)
10007-
*
10008-
* This is called the "coupon collector problem" and H(n) is called the
10009-
* harmonic series. This could be approximated by n * ln(n), but for
10010-
* reasonable numbers of drives we might as well just compute the series.
10011-
*
10012-
* Alternatively we could set the target to the number of pages necessary
10013-
* so that the expected number of active spindles is some arbitrary
10014-
* percentage of the total. This sounds the same but is actually slightly
10015-
* different. The result ends up being ln(1-P)/ln((n-1)/n) where P is
10016-
* that desired fraction.
10017-
*
10018-
* Experimental results show that both of these formulas aren't aggressive
10019-
* enough, but we don't really have any better proposals.
10020-
*
10021-
* Note that if *newval = 0 (disabled), we must set target = 0.
10022-
*----------
10023-
*/
10024-
10025-
for (i=1;i <=*newval;i++)
10026-
new_prefetch_pages+= (double)*newval / (double)i;
9988+
doublenew_prefetch_pages;
100279989

10028-
/* This range check shouldn't fail, but let's be paranoid */
10029-
if (new_prefetch_pages >=0.0&&new_prefetch_pages< (double)INT_MAX)
9990+
if (ComputeIoConcurrency(*newval,&new_prefetch_pages))
100309991
{
100319992
int*myextra= (int*)guc_malloc(ERROR,sizeof(int));
100329993

‎src/bin/psql/tab-complete.c‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1885,7 +1885,7 @@ psql_completion(const char *text, int start, int end)
18851885
pg_strcasecmp(prev_wd,"(")==0)
18861886
{
18871887
staticconstchar*constlist_TABLESPACEOPTIONS[]=
1888-
{"seq_page_cost","random_page_cost",NULL};
1888+
{"seq_page_cost","random_page_cost","effective_io_concurrency",NULL};
18891889

18901890
COMPLETE_WITH_LIST(list_TABLESPACEOPTIONS);
18911891
}

‎src/include/commands/tablespace.h‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -39,6 +39,7 @@ typedef struct TableSpaceOpts
3939
int32vl_len_;/* varlena header (do not touch directly!) */
4040
float8random_page_cost;
4141
float8seq_page_cost;
42+
inteffective_io_concurrency;
4243
}TableSpaceOpts;
4344

4445
externOidCreateTableSpace(CreateTableSpaceStmt*stmt);

‎src/include/nodes/execnodes.h‎

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1424,7 +1424,8 @@ typedef struct BitmapIndexScanState
14241424
*lossy_pages total number of lossy pages retrieved
14251425
*prefetch_iterator iterator for prefetching ahead of current page
14261426
*prefetch_pages # pages prefetch iterator is ahead of current
1427-
*prefetch_target target prefetch distance
1427+
*prefetch_target current target prefetch distance
1428+
*prefetch_maximum maximum value for prefetch_target
14281429
* ----------------
14291430
*/
14301431
typedefstructBitmapHeapScanState
@@ -1439,6 +1440,7 @@ typedef struct BitmapHeapScanState
14391440
TBMIterator*prefetch_iterator;
14401441
intprefetch_pages;
14411442
intprefetch_target;
1443+
intprefetch_maximum;
14421444
}BitmapHeapScanState;
14431445

14441446
/* ----------------

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