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Commitc0386f4

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Release memory allocated by dependency_degree
Calculating degree of a functional dependency may allocate a lot ofmemory - we have released mot of the explicitly allocated memory, bute.g. detoasted varlena values were left behind. That may be an issue,because we consider a lot of dependencies (all combinations), and thedetoasting may happen for each one again.Fixed by calling dependency_degree() in a dedicated context, andresetting it after each call. We only need the calculated dependencydegree, so we don't need to copy anything.Backpatch to PostgreSQL 10, where extended statistics were introduced.Backpatch-through: 10Discussion:https://www.postgresql.org/message-id/20210915200928.GP831%40telsasoft.com
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‎src/backend/statistics/dependencies.c

Lines changed: 16 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -30,6 +30,7 @@
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#include"utils/fmgroids.h"
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#include"utils/fmgrprotos.h"
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#include"utils/lsyscache.h"
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#include"utils/memutils.h"
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#include"utils/selfuncs.h"
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#include"utils/syscache.h"
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#include"utils/typcache.h"
@@ -332,13 +333,6 @@ dependency_degree(int numrows, HeapTuple *rows, int k, AttrNumber *dependency,
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group_size++;
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}
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335-
if (items)
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pfree(items);
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pfree(mss);
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pfree(attnums);
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pfree(attnums_dep);
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/* Compute the 'degree of validity' as (supporting/total). */
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return (n_supporting_rows*1.0 /numrows);
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}
@@ -370,6 +364,7 @@ statext_dependencies_build(int numrows, HeapTuple *rows, Bitmapset *attrs,
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/* result */
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MVDependencies*dependencies=NULL;
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MemoryContextcxt;
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/*
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* Transform the bms into an array, to make accessing i-th member easier.
@@ -378,6 +373,11 @@ statext_dependencies_build(int numrows, HeapTuple *rows, Bitmapset *attrs,
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Assert(numattrs >=2);
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376+
/* tracks memory allocated by dependency_degree calls */
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cxt=AllocSetContextCreate(CurrentMemoryContext,
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"dependency_degree cxt",
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ALLOCSET_DEFAULT_SIZES);
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/*
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* We'll try build functional dependencies starting from the smallest ones
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* covering just 2 columns, to the largest ones, covering all columns
@@ -396,10 +396,17 @@ statext_dependencies_build(int numrows, HeapTuple *rows, Bitmapset *attrs,
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{
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doubledegree;
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MVDependency*d;
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MemoryContextoldcxt;
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/* release memory used by dependency degree calculation */
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oldcxt=MemoryContextSwitchTo(cxt);
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/* compute how valid the dependency seems */
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degree=dependency_degree(numrows,rows,k,dependency,stats,attrs);
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407+
MemoryContextSwitchTo(oldcxt);
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MemoryContextReset(cxt);
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/*
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* if the dependency seems entirely invalid, don't store it
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*/
@@ -441,6 +448,8 @@ statext_dependencies_build(int numrows, HeapTuple *rows, Bitmapset *attrs,
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DependencyGenerator_free(DependencyGenerator);
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}
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MemoryContextDelete(cxt);
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returndependencies;
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}
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