From 4487a7def3ae6efa79c545c3edc03ea97f446e36 Mon Sep 17 00:00:00 2001 From: Tomas Vondra Date: Tue, 21 Sep 2021 01:13:11 +0200 Subject: [PATCH] Release memory allocated by dependency_degree 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 --- src/backend/statistics/dependencies.c | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) diff --git a/src/backend/statistics/dependencies.c b/src/backend/statistics/dependencies.c index e7f2d6c0ca7..445a0db7c5e 100644 --- a/src/backend/statistics/dependencies.c +++ b/src/backend/statistics/dependencies.c @@ -29,6 +29,8 @@ #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" @@ -321,11 +323,6 @@ dependency_degree(int numrows, HeapTuple *rows, int k, AttrNumber *dependency, group_size++; } - pfree(items); - pfree(values); - pfree(isnull); - pfree(mss); - /* Compute the 'degree of validity' as (supporting/total). */ return (n_supporting_rows * 1.0 / numrows); } @@ -358,6 +355,7 @@ statext_dependencies_build(int numrows, HeapTuple *rows, Bitmapset *attrs, /* result */ MVDependencies *dependencies = NULL; + MemoryContext cxt; numattrs = bms_num_members(attrs); @@ -372,6 +370,11 @@ statext_dependencies_build(int numrows, HeapTuple *rows, Bitmapset *attrs, Assert(numattrs >= 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 @@ -390,10 +393,17 @@ statext_dependencies_build(int numrows, HeapTuple *rows, Bitmapset *attrs, { 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(numrows, rows, k, dependency, stats, attrs); + MemoryContextSwitchTo(oldcxt); + MemoryContextReset(cxt); + /* * if the dependency seems entirely invalid, don't store it */ @@ -435,6 +445,8 @@ statext_dependencies_build(int numrows, HeapTuple *rows, Bitmapset *attrs, DependencyGenerator_free(DependencyGenerator); } + MemoryContextDelete(cxt); + return dependencies; }