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Commit616bceb

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Avoid integer overflow in the loop that extracts histogram entries from
ANALYZE's total sample. The original coding is at risk of overflow forstatistics targets exceeding about 2675; this was not a problem before8.4 but it is now. Per bug #4793 from Dennis Noordsij.
1 parent5d540ad commit616bceb

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1 file changed

+28
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‎src/backend/commands/analyze.c

Lines changed: 28 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
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*
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* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.135 2009/03/31 22:12:46 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/commands/analyze.c,v 1.136 2009/05/05 18:02:11 tgl Exp $
1212
*
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*-------------------------------------------------------------------------
1414
*/
@@ -2260,6 +2260,10 @@ compute_scalar_stats(VacAttrStatsP stats,
22602260
MemoryContextold_context;
22612261
Datum*hist_values;
22622262
intnvals;
2263+
intpos,
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posfrac,
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delta,
2266+
deltafrac;
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22642268
/* Sort the MCV items into position order to speed next loop */
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qsort((void*)track,num_mcv,
@@ -2313,15 +2317,35 @@ compute_scalar_stats(VacAttrStatsP stats,
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/* Must copy the target values into anl_context */
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old_context=MemoryContextSwitchTo(stats->anl_context);
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hist_values= (Datum*)palloc(num_hist*sizeof(Datum));
2320+
2321+
/*
2322+
* The object of this loop is to copy the first and last values[]
2323+
* entries along with evenly-spaced values in between. So the
2324+
* i'th value is values[(i * (nvals - 1)) / (num_hist - 1)]. But
2325+
* computing that subscript directly risks integer overflow when
2326+
* the stats target is more than a couple thousand. Instead we
2327+
* add (nvals - 1) / (num_hist - 1) to pos at each step, tracking
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* the integral and fractional parts of the sum separately.
2329+
*/
2330+
delta= (nvals-1) / (num_hist-1);
2331+
deltafrac= (nvals-1) % (num_hist-1);
2332+
pos=posfrac=0;
2333+
23162334
for (i=0;i<num_hist;i++)
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{
2318-
intpos;
2319-
2320-
pos= (i* (nvals-1)) / (num_hist-1);
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hist_values[i]=datumCopy(values[pos].value,
23222337
stats->attr->attbyval,
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stats->attr->attlen);
2339+
pos+=delta;
2340+
posfrac+=deltafrac;
2341+
if (posfrac >= (num_hist-1))
2342+
{
2343+
/* fractional part exceeds 1, carry to integer part */
2344+
pos++;
2345+
posfrac-= (num_hist-1);
2346+
}
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}
2348+
23252349
MemoryContextSwitchTo(old_context);
23262350

23272351
stats->stakind[slot_idx]=STATISTIC_KIND_HISTOGRAM;

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