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Release memory allocated by dependency_degree

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Calculating degree of a functional dependency may allocate a lot of
memory - we have released mot of the explicitly allocated memory, but
e.g. detoasted varlena values were left behind. That may be an issue,
because we consider a lot of dependencies (all combinations), and the
detoasting may happen for each one again.

Fixed by calling dependency_degree() in a dedicated context, and
resetting it after each call. We only need the calculated dependency
degree, so we don't need to copy anything.

Backpatch to PostgreSQL 10, where extended statistics were introduced.

Backpatch-through: 10
Discussion: https://www.postgresql.org/message-id/20210915200928.GP831%40telsasoft.com
This commit is contained in:
Tomas Vondra 2021-09-21 01:13:11 +02:00
parent bb7628e55e
commit abb2f9144b
1 changed files with 16 additions and 6 deletions
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22
src/backend/statistics/dependencies.c
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@ -30,6 +30,7 @@
#include "utils/fmgroids.h"
#include "utils/fmgrprotos.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/selfuncs.h"
#include "utils/syscache.h"
#include "utils/typcache.h"
@ -325,12 +326,6 @@ dependency_degree(StatsBuildData *data, int k, AttrNumber *dependency)
group_size++;
}
if (items)
pfree(items);
pfree(mss);
pfree(attnums_dep);
/* Compute the 'degree of validity' as (supporting/total). */
return (n_supporting_rows * 1.0 / data->numrows);
}
@ -359,9 +354,15 @@ statext_dependencies_build(StatsBuildData *data)
/* result */
MVDependencies *dependencies = NULL;
MemoryContext cxt;
Assert(data->nattnums >= 2);
/* tracks memory allocated by dependency_degree calls */
cxt = AllocSetContextCreate(CurrentMemoryContext,
"dependency_degree cxt",
ALLOCSET_DEFAULT_SIZES);
/*
* We'll try build functional dependencies starting from the smallest ones
* covering just 2 columns, to the largest ones, covering all columns
@ -380,10 +381,17 @@ statext_dependencies_build(StatsBuildData *data)
{
double degree;
MVDependency *d;
MemoryContext oldcxt;
/* release memory used by dependency degree calculation */
oldcxt = MemoryContextSwitchTo(cxt);
/* compute how valid the dependency seems */
degree = dependency_degree(data, k, dependency);
MemoryContextSwitchTo(oldcxt);
MemoryContextReset(cxt);
/*
* if the dependency seems entirely invalid, don't store it
*/
@ -425,6 +433,8 @@ statext_dependencies_build(StatsBuildData *data)
DependencyGenerator_free(DependencyGenerator);
}
MemoryContextDelete(cxt);
return dependencies;
}