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Reduce memory usage of tsvector type analyze function.

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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
This commit is contained in:
Heikki Linnakangas 2017-07-12 22:03:38 +03:00
parent ca793c59a5
commit da11977de9
1 changed files with 17 additions and 4 deletions
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21
src/backend/tsearch/ts_typanalyze.c
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@ -232,9 +232,7 @@ compute_tsvector_stats(VacAttrStats *stats,
/* /*
* We loop through the lexemes in the tsvector and add them to our * We loop through the lexemes in the tsvector and add them to our
* tracking hashtable. Note: the hashtable entries will point into * tracking hashtable.
* the (detoasted) tsvector value, therefore we cannot free that
* storage until we're done.
*/ */
lexemesptr = STRPTR(vector); lexemesptr = STRPTR(vector);
curentryptr = ARRPTR(vector); curentryptr = ARRPTR(vector);
@ -242,7 +240,12 @@ compute_tsvector_stats(VacAttrStats *stats,
{ {
bool found; 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.lexeme = lexemesptr + curentryptr->pos;
hash_key.length = curentryptr->len; hash_key.length = curentryptr->len;
@ -261,6 +264,9 @@ compute_tsvector_stats(VacAttrStats *stats,
/* Initialize new tracking list element */ /* Initialize new tracking list element */
item->frequency = 1; item->frequency = 1;
item->delta = b_current - 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) */ /* 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 */ /* Advance to the next WordEntry in the tsvector */
curentryptr++; 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. */ /* 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) if (item->frequency + item->delta <= b_current)
{ {
char *lexeme = item->key.lexeme;
if (hash_search(lexemes_tab, (const void *) &item->key, if (hash_search(lexemes_tab, (const void *) &item->key,
HASH_REMOVE, NULL) == NULL) HASH_REMOVE, NULL) == NULL)
elog(ERROR, "hash table corrupted"); elog(ERROR, "hash table corrupted");
pfree(lexeme);
} }
} }
} }