From db6736c93cb844d245b726e7a262f2cdcd34612e Mon Sep 17 00:00:00 2001
From: Peter Geoghegan <pg@bowt.ie>
Date: Wed, 12 Jan 2022 15:41:04 -0800
Subject: [PATCH] Fix memory leak in indexUnchanged hint mechanism.
Commit 9dc718bd added a "logically unchanged by UPDATE" hinting
mechanism, which is currently used within nbtree indexes only (see
commit d168b666). This mechanism determined whether or not the incoming
item is a logically unchanged duplicate (a duplicate needed only for
MVCC versioning purposes) once per row updated per non-HOT update. This
approach led to memory leaks which were noticeable with an UPDATE
statement that updated sufficiently many rows, at least on tables that
happen to have an expression index.
On HEAD, fix the issue by adding a cache to the executor's per-index
IndexInfo struct.
Take a different approach on Postgres 14 to avoid an ABI break: simply
pass down the hint to all indexes unconditionally with non-HOT UPDATEs.
This is deemed acceptable because the hint is currently interpreted
within btinsert() as "perform a bottom-up index deletion pass if and
when the only alternative is splitting the leaf page -- prefer to delete
any LP_DEAD-set items first". nbtree must always treat the hint as a
noisy signal about what might work, as a strategy of last resort, with
costs imposed on non-HOT updaters. (The same thing might not be true
within another index AM that applies the hint, which is why the original
behavior is preserved on HEAD.)
Author: Peter Geoghegan <pg@bowt.ie>
Reported-By: Klaudie Willis <Klaudie.Willis@protonmail.com>
Diagnosed-By: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/261065.1639497535@sss.pgh.pa.us
Backpatch: 14-, where the hinting mechanism was added.
---
src/backend/catalog/toasting.c | 2 ++
src/backend/executor/execIndexing.c | 31 +++++++++++++++++++++++++++--
src/backend/nodes/makefuncs.c | 2 ++
src/include/nodes/execnodes.h | 4 ++++
4 files changed, 37 insertions(+), 2 deletions(-)
diff --git a/src/backend/catalog/toasting.c b/src/backend/catalog/toasting.c
index 917bb3577e..3c27cb1e71 100644
--- a/src/backend/catalog/toasting.c
+++ b/src/backend/catalog/toasting.c
@@ -302,6 +302,8 @@ create_toast_table(Relation rel, Oid toastOid, Oid toastIndexOid,
indexInfo->ii_OpclassOptions = NULL;
indexInfo->ii_Unique = true;
indexInfo->ii_ReadyForInserts = true;
+ indexInfo->ii_CheckedUnchanged = false;
+ indexInfo->ii_IndexUnchanged = false;
indexInfo->ii_Concurrent = false;
indexInfo->ii_BrokenHotChain = false;
indexInfo->ii_ParallelWorkers = 0;
diff --git a/src/backend/executor/execIndexing.c b/src/backend/executor/execIndexing.c
index 22eda9449f..0cb0b8f111 100644
--- a/src/backend/executor/execIndexing.c
+++ b/src/backend/executor/execIndexing.c
@@ -935,19 +935,32 @@ static bool
index_unchanged_by_update(ResultRelInfo *resultRelInfo, EState *estate,
IndexInfo *indexInfo, Relation indexRelation)
{
- Bitmapset *updatedCols = ExecGetUpdatedCols(resultRelInfo, estate);
- Bitmapset *extraUpdatedCols = ExecGetExtraUpdatedCols(resultRelInfo, estate);
+ Bitmapset *updatedCols;
+ Bitmapset *extraUpdatedCols;
Bitmapset *allUpdatedCols;
bool hasexpression = false;
List *idxExprs;
+ /*
+ * Check cache first
+ */
+ if (indexInfo->ii_CheckedUnchanged)
+ return indexInfo->ii_IndexUnchanged;
+ indexInfo->ii_CheckedUnchanged = true;
+
/*
* Check for indexed attribute overlap with updated columns.
*
* Only do this for key columns. A change to a non-key column within an
* INCLUDE index should not be counted here. Non-key column values are
* opaque payload state to the index AM, a little like an extra table TID.
+ *
+ * Note that row-level BEFORE triggers won't affect our behavior, since
+ * they don't affect the updatedCols bitmaps generally. It doesn't seem
+ * worth the trouble of checking which attributes were changed directly.
*/
+ updatedCols = ExecGetUpdatedCols(resultRelInfo, estate);
+ extraUpdatedCols = ExecGetExtraUpdatedCols(resultRelInfo, estate);
for (int attr = 0; attr < indexInfo->ii_NumIndexKeyAttrs; attr++)
{
int keycol = indexInfo->ii_IndexAttrNumbers[attr];
@@ -968,6 +981,7 @@ index_unchanged_by_update(ResultRelInfo *resultRelInfo, EState *estate,
extraUpdatedCols))
{
/* Changed key column -- don't hint for this index */
+ indexInfo->ii_IndexUnchanged = false;
return false;
}
}
@@ -981,7 +995,10 @@ index_unchanged_by_update(ResultRelInfo *resultRelInfo, EState *estate,
* shows that the index as a whole is logically unchanged by UPDATE.
*/
if (!hasexpression)
+ {
+ indexInfo->ii_IndexUnchanged = true;
return true;
+ }
/*
* Need to pass only one bms to expression_tree_walker helper function.
@@ -1008,8 +1025,18 @@ index_unchanged_by_update(ResultRelInfo *resultRelInfo, EState *estate,
bms_free(allUpdatedCols);
if (hasexpression)
+ {
+ indexInfo->ii_IndexUnchanged = false;
return false;
+ }
+ /*
+ * Deliberately don't consider index predicates. We should even give the
+ * hint when result rel's "updated tuple" has no corresponding index
+ * tuple, which is possible with a partial index (provided the usual
+ * conditions are met).
+ */
+ indexInfo->ii_IndexUnchanged = true;
return true;
}
diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index dace4f7e2d..822395625b 100644
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -751,6 +751,8 @@ makeIndexInfo(int numattrs, int numkeyattrs, Oid amoid, List *expressions,
Assert(n->ii_NumIndexKeyAttrs <= n->ii_NumIndexAttrs);
n->ii_Unique = unique;
n->ii_ReadyForInserts = isready;
+ n->ii_CheckedUnchanged = false;
+ n->ii_IndexUnchanged = false;
n->ii_Concurrent = concurrent;
/* expressions */
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 8429a9c55d..4ea8735dd8 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -142,6 +142,8 @@ typedef struct ExprState
* Unique is it a unique index?
* OpclassOptions opclass-specific options, or NULL if none
* ReadyForInserts is it valid for inserts?
+ * CheckedUnchanged IndexUnchanged status determined yet?
+ * IndexUnchanged aminsert hint, cached for retail inserts
* Concurrent are we doing a concurrent index build?
* BrokenHotChain did we detect any broken HOT chains?
* ParallelWorkers # of workers requested (excludes leader)
@@ -172,6 +174,8 @@ typedef struct IndexInfo
Datum *ii_OpclassOptions; /* array with one entry per column */
bool ii_Unique;
bool ii_ReadyForInserts;
+ bool ii_CheckedUnchanged;
+ bool ii_IndexUnchanged;
bool ii_Concurrent;
bool ii_BrokenHotChain;
int ii_ParallelWorkers;