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Commitda11977

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Reduce memory usage of tsvector type analyze function.
compute_tsvector_stats() detoasted and kept in memory every tsvector valuein the sample, but that can be a lot of memory. The original bug reportdescribed 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/pfreeoverhead, when you have a lot of distinct lexemes in the sample, but it'sbetter than running out of memory.Fixes bug #14654 reported by James C. Reviewed by Tom Lane. Backport toall supported versions.Discussion:https://www.postgresql.org/message-id/20170514200602.1451.46797@wrigleys.postgresql.org
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‎src/backend/tsearch/ts_typanalyze.c‎

Lines changed: 17 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -232,17 +232,20 @@ compute_tsvector_stats(VacAttrStats *stats,
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/*
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* We loop through the lexemes in the tsvector and add them to our
235-
* tracking hashtable. Note: the hashtable entries will point into
236-
* the (detoasted) tsvector value, therefore we cannot free that
237-
* storage until we're done.
235+
* tracking hashtable.
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*/
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lexemesptr=STRPTR(vector);
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curentryptr=ARRPTR(vector);
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for (j=0;j<vector->size;j++)
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{
243241
boolfound;
244242

245-
/* Construct a hash key */
243+
/*
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* Construct a hash key. The key points into the (detoasted)
245+
* tsvector value at this point, but if a new entry is created, we
246+
* make a copy of it. This way we can free the tsvector value
247+
* once we've processed all its lexemes.
248+
*/
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hash_key.lexeme=lexemesptr+curentryptr->pos;
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hash_key.length=curentryptr->len;
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@@ -261,6 +264,9 @@ compute_tsvector_stats(VacAttrStats *stats,
261264
/* Initialize new tracking list element */
262265
item->frequency=1;
263266
item->delta=b_current-1;
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268+
item->key.lexeme=palloc(hash_key.length);
269+
memcpy(item->key.lexeme,hash_key.lexeme,hash_key.length);
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}
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/* lexeme_no is the number of elements processed (ie N) */
@@ -276,6 +282,10 @@ compute_tsvector_stats(VacAttrStats *stats,
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/* Advance to the next WordEntry in the tsvector */
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curentryptr++;
278284
}
285+
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/* If the vector was toasted, free the detoasted copy. */
287+
if (TSVectorGetDatum(vector)!=value)
288+
pfree(vector);
279289
}
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281291
/* 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)
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{
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if (item->frequency+item->delta <=b_current)
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{
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char*lexeme=item->key.lexeme;
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450462
if (hash_search(lexemes_tab, (constvoid*)&item->key,
451463
HASH_REMOVE,NULL)==NULL)
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elog(ERROR,"hash table corrupted");
465+
pfree(lexeme);
453466
}
454467
}
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}

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