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Allow setting statistics target for extended statistics

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When building statistics, we need to decide how many rows to sample and
how accurate the resulting statistics should be. Until now, it was not
possible to explicitly define statistics target for extended statistics
objects, the value was always computed from the per-attribute targets
with a fallback to the system-wide default statistics target.

That's a bit inconvenient, as it ties together the statistics target set
for per-column and extended statistics. In some cases it may be useful
to require larger sample / higher accuracy for extended statics (or the
other way around), but with this approach that's not possible.

So this commit introduces a new command, allowing to specify statistics
target for individual extended statistics objects, overriding the value
derived from per-attribute targets (and the system default).

  ALTER STATISTICS stat_name SET STATISTICS target_value;

When determining statistics target for an extended statistics object we
first look at this explicitly set value. When this value is -1, we fall
back to the old formula, looking at the per-attribute targets first and
then the system default. This means the behavior is backwards compatible
with older PostgreSQL releases.

Author: Tomas Vondra
Discussion: https://postgr.es/m/20190618213357.vli3i23vpkset2xd@development
Reviewed-by: Kirk Jamison, Dean Rasheed
This commit is contained in:
Tomas Vondra
2019-09-10 20:09:27 +02:00
parent bca6e64354
commit d06215d03b
22 changed files with 458 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files

108
src/backend/commands/statscmds.c
View File

@@ -14,6 +14,7 @@
*/
#include "postgres.h"
#include "access/heapam.h"
#include "access/relation.h"
#include "access/relscan.h"
#include "access/table.h"
@@ -21,6 +22,7 @@
#include "catalog/dependency.h"
#include "catalog/indexing.h"
#include "catalog/namespace.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_statistic_ext.h"
#include "catalog/pg_statistic_ext_data.h"
@@ -29,6 +31,7 @@
#include "miscadmin.h"
#include "statistics/statistics.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/inval.h"
#include "utils/memutils.h"
#include "utils/rel.h"
@@ -336,6 +339,7 @@ CreateStatistics(CreateStatsStmt *stmt)
values[Anum_pg_statistic_ext_stxrelid - 1] = ObjectIdGetDatum(relid);
values[Anum_pg_statistic_ext_stxname - 1] = NameGetDatum(&stxname);
values[Anum_pg_statistic_ext_stxnamespace - 1] = ObjectIdGetDatum(namespaceId);
values[Anum_pg_statistic_ext_stxstattarget - 1] = Int32GetDatum(-1);
values[Anum_pg_statistic_ext_stxowner - 1] = ObjectIdGetDatum(stxowner);
values[Anum_pg_statistic_ext_stxkeys - 1] = PointerGetDatum(stxkeys);
values[Anum_pg_statistic_ext_stxkind - 1] = PointerGetDatum(stxkind);
@@ -414,6 +418,110 @@ CreateStatistics(CreateStatsStmt *stmt)
return myself;
}
/*
* ALTER STATISTICS
*/
ObjectAddress
AlterStatistics(AlterStatsStmt *stmt)
{
Relation rel;
Oid stxoid;
HeapTuple oldtup;
HeapTuple newtup;
Datum repl_val[Natts_pg_statistic_ext];
bool repl_null[Natts_pg_statistic_ext];
bool repl_repl[Natts_pg_statistic_ext];
ObjectAddress address;
int newtarget = stmt->stxstattarget;
/* Limit statistics target to a sane range */
if (newtarget < -1)
{
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("statistics target %d is too low",
newtarget)));
}
else if (newtarget > 10000)
{
newtarget = 10000;
ereport(WARNING,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("lowering statistics target to %d",
newtarget)));
}
/* lookup OID of the statistics object */
stxoid = get_statistics_object_oid(stmt->defnames, stmt->missing_ok);
/*
* If we got here and the OID is not valid, it means the statistics
* does not exist, but the command specified IF EXISTS. So report
* this as a simple NOTICE and we're done.
*/
if (!OidIsValid(stxoid))
{
char *schemaname;
char *statname;
Assert(stmt->missing_ok);
DeconstructQualifiedName(stmt->defnames, &schemaname, &statname);
if (schemaname)
ereport(NOTICE,
(errmsg("statistics object \"%s.%s\" does not exist, skipping",
schemaname, statname)));
else
ereport(NOTICE,
(errmsg("statistics object \"%s\" does not exist, skipping",
statname)));
return InvalidObjectAddress;
}
/* Search pg_statistic_ext */
rel = table_open(StatisticExtRelationId, RowExclusiveLock);
oldtup = SearchSysCache1(STATEXTOID, ObjectIdGetDatum(stxoid));
/* Must be owner of the existing statistics object */
if (!pg_statistics_object_ownercheck(stxoid, GetUserId()))
aclcheck_error(ACLCHECK_NOT_OWNER, OBJECT_STATISTIC_EXT,
NameListToString(stmt->defnames));
/* Build new tuple. */
memset(repl_val, 0, sizeof(repl_val));
memset(repl_null, false, sizeof(repl_null));
memset(repl_repl, false, sizeof(repl_repl));
/* replace the stxstattarget column */
repl_repl[Anum_pg_statistic_ext_stxstattarget - 1] = true;
repl_val[Anum_pg_statistic_ext_stxstattarget - 1] = Int32GetDatum(newtarget);
newtup = heap_modify_tuple(oldtup, RelationGetDescr(rel),
repl_val, repl_null, repl_repl);
/* Update system catalog. */
CatalogTupleUpdate(rel, &newtup->t_self, newtup);
InvokeObjectPostAlterHook(StatisticExtRelationId, stxoid, 0);
ObjectAddressSet(address, StatisticExtRelationId, stxoid);
/*
* NOTE: because we only support altering the statistics target, not the
* other fields, there is no need to update dependencies.
*/
heap_freetuple(newtup);
ReleaseSysCache(oldtup);
table_close(rel, RowExclusiveLock);
return address;
}
/*
* Guts of statistics object deletion.
*/