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Commit4bc6fb5

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Fix integer overflow bug in GiST buffering build calculations.
The result of (maintenance_work_mem * 1024) / BLCKSZ doesn't fit in a signed32-bit integer, if maintenance_work_mem >= 2GB. Use double instead. Andwhile we're at it, write the calculations in an easier to understand form,with the intermediary steps written out and commented.
1 parent2755abf commit4bc6fb5

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‎src/backend/access/gist/gistbuild.c

Lines changed: 23 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -323,8 +323,8 @@ gistInitBuffering(GISTBuildState *buildstate)
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* calculating levelStep is very close to Arge et al's formula. For a
324324
* large B, our formula gives a value that is 2x higher.
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*
326-
* The average size of a subtree of depth n can be calculated as a
327-
* geometric series:
326+
* The average size(in pages)of a subtree of depth n can be calculated
327+
*as ageometric series:
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*
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* B^0 + B^1 + B^2 + ... + B^n = (1 - B^(n + 1)) / (1 - B)
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*
@@ -353,14 +353,28 @@ gistInitBuffering(GISTBuildState *buildstate)
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* the hash table.
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*/
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levelStep=1;
356-
while (
357-
/* subtree must fit in cache (with safety factor of 4) */
358-
(1-pow(avgIndexTuplesPerPage, (double) (levelStep+1))) / (1-avgIndexTuplesPerPage)<effective_cache_size /4
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&&
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/* each node in the lowest level of a subtree has one page in memory */
361-
(pow(maxIndexTuplesPerPage, (double)levelStep)< (maintenance_work_mem*1024) /BLCKSZ)
362-
)
356+
for (;;)
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{
358+
doublesubtreesize;
359+
doublemaxlowestlevelpages;
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361+
/* size of an average subtree at this levelStep (in pages). */
362+
subtreesize=
363+
(1-pow(avgIndexTuplesPerPage, (double) (levelStep+1))) /
364+
(1-avgIndexTuplesPerPage);
365+
366+
/* max number of pages at the lowest level of a subtree */
367+
maxlowestlevelpages=pow(maxIndexTuplesPerPage, (double)levelStep);
368+
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/* subtree must fit in cache (with safety factor of 4) */
370+
if (subtreesize>effective_cache_size /4)
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break;
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373+
/* each node in the lowest level of a subtree has one page in memory */
374+
if (maxlowestlevelpages> ((double)maintenance_work_mem*1024) /BLCKSZ)
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break;
376+
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/* Good, we can handle this levelStep. See if we can go one higher. */
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levelStep++;
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}
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