From da11977de9c685ef808d3a293727f9ce26753ec4 Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Wed, 12 Jul 2017 22:03:38 +0300
Subject: [PATCH] Reduce memory usage of tsvector type analyze function.
compute_tsvector_stats() detoasted and kept in memory every tsvector value
in the sample, but that can be a lot of memory. The original bug report
described a case using over 10 gigabytes, with statistics target of 10000
(the maximum).
To fix, allocate a separate copy of just the lexemes that we keep around,
and free the detoasted tsvector values as we go. This adds some palloc/pfree
overhead, when you have a lot of distinct lexemes in the sample, but it's
better than running out of memory.
Fixes bug #14654 reported by James C. Reviewed by Tom Lane. Backport to
all supported versions.
Discussion: https://www.postgresql.org/message-id/20170514200602.1451.46797@wrigleys.postgresql.org
---
src/backend/tsearch/ts_typanalyze.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/src/backend/tsearch/ts_typanalyze.c b/src/backend/tsearch/ts_typanalyze.c
index ab224b76b8..320c7f1a61 100644
--- a/src/backend/tsearch/ts_typanalyze.c
+++ b/src/backend/tsearch/ts_typanalyze.c
@@ -232,9 +232,7 @@ compute_tsvector_stats(VacAttrStats *stats,
/*
* We loop through the lexemes in the tsvector and add them to our
- * tracking hashtable. Note: the hashtable entries will point into
- * the (detoasted) tsvector value, therefore we cannot free that
- * storage until we're done.
+ * tracking hashtable.
*/
lexemesptr = STRPTR(vector);
curentryptr = ARRPTR(vector);
@@ -242,7 +240,12 @@ compute_tsvector_stats(VacAttrStats *stats,
{
bool found;
- /* Construct a hash key */
+ /*
+ * Construct a hash key. The key points into the (detoasted)
+ * tsvector value at this point, but if a new entry is created, we
+ * make a copy of it. This way we can free the tsvector value
+ * once we've processed all its lexemes.
+ */
hash_key.lexeme = lexemesptr + curentryptr->pos;
hash_key.length = curentryptr->len;
@@ -261,6 +264,9 @@ compute_tsvector_stats(VacAttrStats *stats,
/* Initialize new tracking list element */
item->frequency = 1;
item->delta = b_current - 1;
+
+ item->key.lexeme = palloc(hash_key.length);
+ memcpy(item->key.lexeme, hash_key.lexeme, hash_key.length);
}
/* lexeme_no is the number of elements processed (ie N) */
@@ -276,6 +282,10 @@ compute_tsvector_stats(VacAttrStats *stats,
/* Advance to the next WordEntry in the tsvector */
curentryptr++;
}
+
+ /* If the vector was toasted, free the detoasted copy. */
+ if (TSVectorGetDatum(vector) != value)
+ pfree(vector);
}
/* We can only compute real stats if we found some non-null values. */
@@ -447,9 +457,12 @@ prune_lexemes_hashtable(HTAB *lexemes_tab, int b_current)
{
if (item->frequency + item->delta <= b_current)
{
+ char *lexeme = item->key.lexeme;
+
if (hash_search(lexemes_tab, (const void *) &item->key,
HASH_REMOVE, NULL) == NULL)
elog(ERROR, "hash table corrupted");
+ pfree(lexeme);
}
}
}