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Introduce a maintenance_io_concurrency setting.
Introduce a GUC and a tablespace option to control I/O prefetching, much like effective_io_concurrency, but for work that is done on behalf of many client sessions. Use the new setting in heapam.c instead of the hard-coded formula effective_io_concurrency + 10 introduced by commit 558a916. Go with a default value of 10 for now, because it's a round number pretty close to the value used for that existing case. Discussion: https://postgr.es/m/CA%2BhUKGJUw08dPs_3EUcdO6M90GnjofPYrWp4YSLaBkgYwS-AqA%40mail.gmail.com
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-23
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‎doc/src/sgml/config.sgml

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2229,6 +2229,26 @@ include_dir 'conf.d'
22292229
</listitem>
22302230
</varlistentry>
22312231

2232+
<varlistentry id="guc-maintenance-io-concurrency" xreflabel="maintenance_io_concurrency">
2233+
<term><varname>maintenance_io_concurrency</varname> (<type>integer</type>)
2234+
<indexterm>
2235+
<primary><varname>maintenance_io_concurrency</varname> configuration parameter</primary>
2236+
</indexterm>
2237+
</term>
2238+
<listitem>
2239+
<para>
2240+
Similar to <varname>effective_io_concurrency</varname>, but used
2241+
for maintenance work that is done on behalf of many client sessions.
2242+
</para>
2243+
<para>
2244+
The default is 10 on supported systems, otherwise 0. This value can
2245+
be overridden for tables in a particular tablespace by setting the
2246+
tablespace parameter of the same name (see
2247+
<xref linkend="sql-altertablespace"/>).
2248+
</para>
2249+
</listitem>
2250+
</varlistentry>
2251+
22322252
<varlistentry id="guc-max-worker-processes" xreflabel="max_worker_processes">
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<term><varname>max_worker_processes</varname> (<type>integer</type>)
22342254
<indexterm>

‎doc/src/sgml/ref/alter_tablespace.sgml

Lines changed: 7 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -84,13 +84,16 @@ ALTER TABLESPACE <replaceable>name</replaceable> RESET ( <replaceable class="par
8484
<para>
8585
A tablespace parameter to be set or reset. Currently, the only
8686
available parameters are <varname>seq_page_cost</varname>,
87-
<varname>random_page_cost</varname> and <varname>effective_io_concurrency</varname>.
88-
Setting either value for a particular tablespace will override the
87+
<varname>random_page_cost</varname>, <varname>effective_io_concurrency</varname>
88+
and <varname>maintenance_io_concurrency</varname>.
89+
Setting these values for a particular tablespace will override the
8990
planner's usual estimate of the cost of reading pages from tables in
90-
that tablespace, as established by the configuration parameters of the
91+
that tablespace, and the executor's prefetching behavior, as established
92+
by the configuration parameters of the
9193
same name (see <xref linkend="guc-seq-page-cost"/>,
9294
<xref linkend="guc-random-page-cost"/>,
93-
<xref linkend="guc-effective-io-concurrency"/>). This may be useful if
95+
<xref linkend="guc-effective-io-concurrency"/>,
96+
<xref linkend="guc-maintenance-io-concurrency"/>). This may be useful if
9497
one tablespace is located on a disk which is faster or slower than the
9598
remainder of the I/O subsystem.
9699
</para>

‎doc/src/sgml/ref/create_tablespace.sgml

Lines changed: 7 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -106,13 +106,16 @@ CREATE TABLESPACE <replaceable class="parameter">tablespace_name</replaceable>
106106
<para>
107107
A tablespace parameter to be set or reset. Currently, the only
108108
available parameters are <varname>seq_page_cost</varname>,
109-
<varname>random_page_cost</varname> and <varname>effective_io_concurrency</varname>.
110-
Setting either value for a particular tablespace will override the
109+
<varname>random_page_cost</varname>, <varname>effective_io_concurrency</varname>
110+
and <varname>maintenance_io_concurrency</varname>.
111+
Setting these values for a particular tablespace will override the
111112
planner's usual estimate of the cost of reading pages from tables in
112-
that tablespace, as established by the configuration parameters of the
113+
that tablespace, and the executor's prefetching behavior, as established
114+
by the configuration parameters of the
113115
same name (see <xref linkend="guc-seq-page-cost"/>,
114116
<xref linkend="guc-random-page-cost"/>,
115-
<xref linkend="guc-effective-io-concurrency"/>). This may be useful if
117+
<xref linkend="guc-effective-io-concurrency"/>,
118+
<xref linkend="guc-maintenance-io-concurrency"/>). This may be useful if
116119
one tablespace is located on a disk which is faster or slower than the
117120
remainder of the I/O subsystem.
118121
</para>

‎src/backend/access/common/reloptions.c

Lines changed: 15 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -349,6 +349,19 @@ static relopt_int intRelOpts[] =
349349
-1, 0, MAX_IO_CONCURRENCY
350350
#else
351351
0, 0, 0
352+
#endif
353+
},
354+
{
355+
{
356+
"maintenance_io_concurrency",
357+
"Number of simultaneous requests that can be handled efficiently by the disk subsystem for maintenance work.",
358+
RELOPT_KIND_TABLESPACE,
359+
ShareUpdateExclusiveLock
360+
},
361+
#ifdef USE_PREFETCH
362+
-1, 0, MAX_IO_CONCURRENCY
363+
#else
364+
0, 0, 0
352365
#endif
353366
},
354367
{
@@ -1700,7 +1713,8 @@ tablespace_reloptions(Datum reloptions, bool validate)
17001713
static const relopt_parse_elt tab[] = {
17011714
{"random_page_cost", RELOPT_TYPE_REAL, offsetof(TableSpaceOpts, random_page_cost)},
17021715
{"seq_page_cost", RELOPT_TYPE_REAL, offsetof(TableSpaceOpts, seq_page_cost)},
1703-
{"effective_io_concurrency", RELOPT_TYPE_INT, offsetof(TableSpaceOpts, effective_io_concurrency)}
1716+
{"effective_io_concurrency", RELOPT_TYPE_INT, offsetof(TableSpaceOpts, effective_io_concurrency)},
1717+
{"maintenance_io_concurrency", RELOPT_TYPE_INT, offsetof(TableSpaceOpts, maintenance_io_concurrency)}
17041718
};
17051719

17061720
return (bytea *) build_reloptions(reloptions, validate,

‎src/backend/access/heap/heapam.c

Lines changed: 3 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -7003,7 +7003,6 @@ heap_compute_xid_horizon_for_tuples(Relation rel,
70037003
Page hpage;
70047004
#ifdef USE_PREFETCH
70057005
XidHorizonPrefetchState prefetch_state;
7006-
int io_concurrency;
70077006
int prefetch_distance;
70087007
#endif
70097008

@@ -7026,24 +7025,15 @@ heap_compute_xid_horizon_for_tuples(Relation rel,
70267025
/*
70277026
* Compute the prefetch distance that we will attempt to maintain.
70287027
*
7029-
* We don't use the regular formula to determine how much to prefetch
7030-
* here, but instead just add a constant to effective_io_concurrency.
7031-
* That's because it seems best to do some prefetching here even when
7032-
* effective_io_concurrency is set to 0, but if the DBA thinks it's OK to
7033-
* do more prefetching for other operations, then it's probably OK to do
7034-
* more prefetching in this case, too. It may be that this formula is too
7035-
* simplistic, but at the moment there is no evidence of that or any idea
7036-
* about what would work better.
7037-
*
70387028
* Since the caller holds a buffer lock somewhere in rel, we'd better make
70397029
* sure that isn't a catalog relation before we call code that does
70407030
* syscache lookups, to avoid risk of deadlock.
70417031
*/
70427032
if (IsCatalogRelation(rel))
7043-
io_concurrency = effective_io_concurrency;
7033+
prefetch_distance = maintenance_io_concurrency;
70447034
else
7045-
io_concurrency = get_tablespace_io_concurrency(rel->rd_rel->reltablespace);
7046-
prefetch_distance = Min((io_concurrency) + 10, MAX_IO_CONCURRENCY);
7035+
prefetch_distance =
7036+
get_tablespace_maintenance_io_concurrency(rel->rd_rel->reltablespace);
70477037

70487038
/* Start prefetching. */
70497039
xid_horizon_prefetch_buffer(rel, &prefetch_state, prefetch_distance);

‎src/backend/storage/buffer/bufmgr.c

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -119,6 +119,13 @@ bool track_io_timing = false;
119119
*/
120120
int effective_io_concurrency = 0;
121121

122+
/*
123+
* Like effective_io_concurrency, but used by maintenance code paths that might
124+
* benefit from a higher setting because they work on behalf of many sessions.
125+
* Overridden by the tablespace setting of the same name.
126+
*/
127+
int maintenance_io_concurrency = 0;
128+
122129
/*
123130
* GUC variables about triggering kernel writeback for buffers written; OS
124131
* dependent defaults are set via the GUC mechanism.

‎src/backend/utils/cache/spccache.c

Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -221,3 +221,17 @@ get_tablespace_io_concurrency(Oid spcid)
221221
else
222222
return spc->opts->effective_io_concurrency;
223223
}
224+
225+
/*
226+
* get_tablespace_maintenance_io_concurrency
227+
*/
228+
int
229+
get_tablespace_maintenance_io_concurrency(Oid spcid)
230+
{
231+
TableSpaceCacheEntry *spc = get_tablespace(spcid);
232+
233+
if (!spc->opts || spc->opts->maintenance_io_concurrency < 0)
234+
return maintenance_io_concurrency;
235+
else
236+
return spc->opts->maintenance_io_concurrency;
237+
}

‎src/backend/utils/misc/guc.c

Lines changed: 32 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -196,6 +196,7 @@ static bool check_autovacuum_max_workers(int *newval, void **extra, GucSource so
196196
static bool check_max_wal_senders(int *newval, void **extra, GucSource source);
197197
static bool check_autovacuum_work_mem(int *newval, void **extra, GucSource source);
198198
static bool check_effective_io_concurrency(int *newval, void **extra, GucSource source);
199+
static bool check_maintenance_io_concurrency(int *newval, void **extra, GucSource source);
199200
static void assign_pgstat_temp_directory(const char *newval, void *extra);
200201
static bool check_application_name(char **newval, void **extra, GucSource source);
201202
static void assign_application_name(const char *newval, void *extra);
@@ -2884,6 +2885,24 @@ static struct config_int ConfigureNamesInt[] =
28842885
check_effective_io_concurrency, NULL, NULL
28852886
},
28862887

2888+
{
2889+
{"maintenance_io_concurrency",
2890+
PGC_USERSET,
2891+
RESOURCES_ASYNCHRONOUS,
2892+
gettext_noop("A variant of effective_io_concurrency that is used for maintenance work."),
2893+
NULL,
2894+
GUC_EXPLAIN
2895+
},
2896+
&maintenance_io_concurrency,
2897+
#ifdef USE_PREFETCH
2898+
10,
2899+
#else
2900+
0,
2901+
#endif
2902+
0, MAX_IO_CONCURRENCY,
2903+
check_maintenance_io_concurrency, NULL, NULL
2904+
},
2905+
28872906
{
28882907
{"backend_flush_after", PGC_USERSET, RESOURCES_ASYNCHRONOUS,
28892908
gettext_noop("Number of pages after which previously performed writes are flushed to disk."),
@@ -11466,6 +11485,19 @@ check_effective_io_concurrency(int *newval, void **extra, GucSource source)
1146611485
return true;
1146711486
}
1146811487

11488+
static bool
11489+
check_maintenance_io_concurrency(int *newval, void **extra, GucSource source)
11490+
{
11491+
#ifndef USE_PREFETCH
11492+
if (*newval != 0)
11493+
{
11494+
GUC_check_errdetail("maintenance_io_concurrency must be set to 0 on platforms that lack posix_fadvise().");
11495+
return false;
11496+
}
11497+
#endif /* USE_PREFETCH */
11498+
return true;
11499+
}
11500+
1146911501
static void
1147011502
assign_pgstat_temp_directory(const char *newval, void *extra)
1147111503
{

‎src/bin/psql/tab-complete.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -2140,7 +2140,7 @@ psql_completion(const char *text, int start, int end)
21402140
/* ALTER TABLESPACE <foo> SET|RESET ( */
21412141
else if (Matches("ALTER", "TABLESPACE", MatchAny, "SET|RESET", "("))
21422142
COMPLETE_WITH("seq_page_cost", "random_page_cost",
2143-
"effective_io_concurrency");
2143+
"effective_io_concurrency", "maintenance_io_concurrency");
21442144

21452145
/* ALTER TEXT SEARCH */
21462146
else if (Matches("ALTER", "TEXT", "SEARCH"))

‎src/include/commands/tablespace.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -40,6 +40,7 @@ typedef struct TableSpaceOpts
4040
float8 random_page_cost;
4141
float8 seq_page_cost;
4242
int effective_io_concurrency;
43+
int maintenance_io_concurrency;
4344
} TableSpaceOpts;
4445

4546
extern Oid CreateTableSpace(CreateTableSpaceStmt *stmt);

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