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Commitb36df04

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Guard against roundoff errors in new selectivity-estimation code,
per bug report from Laurette Cisneros.
1 parentbb2bff4 commitb36df04

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1 file changed

+34
-22
lines changed

1 file changed

+34
-22
lines changed

‎src/backend/utils/adt/selfuncs.c‎

Lines changed: 34 additions & 22 deletions
Original file line numberDiff line numberDiff line change
@@ -15,7 +15,7 @@
1515
*
1616
*
1717
* IDENTIFICATION
18-
* $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.102 2001/11/05 17:46:29 momjian Exp $
18+
* $Header: /cvsroot/pgsql/src/backend/utils/adt/selfuncs.c,v 1.103 2002/01/03 04:02:34 tgl Exp $
1919
*
2020
*-------------------------------------------------------------------------
2121
*/
@@ -124,6 +124,19 @@
124124
#defineDEFAULT_NOT_UNK_SEL(1.0 - DEFAULT_UNK_SEL)
125125
#defineDEFAULT_BOOL_SEL0.5
126126

127+
/*
128+
* Clamp a computed probability estimate (which may suffer from roundoff or
129+
* estimation errors) to valid range. Argument must be a float variable.
130+
*/
131+
#defineCLAMP_PROBABILITY(p) \
132+
do { \
133+
if (p < 0.0) \
134+
p = 0.0; \
135+
else if (p > 1.0) \
136+
p = 1.0; \
137+
} while (0)
138+
139+
127140
staticboolconvert_to_scalar(Datumvalue,Oidvaluetypid,double*scaledvalue,
128141
Datumlobound,Datumhibound,Oidboundstypid,
129142
double*scaledlobound,double*scaledhibound);
@@ -285,6 +298,7 @@ eqsel(PG_FUNCTION_ARGS)
285298
for (i=0;i<nnumbers;i++)
286299
sumcommon+=numbers[i];
287300
selec=1.0-sumcommon-stats->stanullfrac;
301+
CLAMP_PROBABILITY(selec);
288302

289303
/*
290304
* and in fact it's probably a good deal less. We
@@ -356,10 +370,7 @@ eqsel(PG_FUNCTION_ARGS)
356370
}
357371

358372
/* result should be in range, but make sure... */
359-
if (selec<0.0)
360-
selec=0.0;
361-
elseif (selec>1.0)
362-
selec=1.0;
373+
CLAMP_PROBABILITY(selec);
363374

364375
PG_RETURN_FLOAT8((float8)selec);
365376
}
@@ -669,10 +680,7 @@ scalarineqsel(Query *root, Oid operator, bool isgt,
669680
ReleaseSysCache(statsTuple);
670681

671682
/* result should be in range, but make sure... */
672-
if (selec<0.0)
673-
selec=0.0;
674-
elseif (selec>1.0)
675-
selec=1.0;
683+
CLAMP_PROBABILITY(selec);
676684

677685
returnselec;
678686
}
@@ -867,10 +875,7 @@ patternsel(PG_FUNCTION_ARGS, Pattern_Type ptype)
867875
restsel=pattern_selectivity(rest,ptype);
868876
selec=prefixsel*restsel;
869877
/* result should be in range, but make sure... */
870-
if (selec<0.0)
871-
selec=0.0;
872-
elseif (selec>1.0)
873-
selec=1.0;
878+
CLAMP_PROBABILITY(selec);
874879
result=selec;
875880
}
876881

@@ -1179,10 +1184,7 @@ booltestsel(Query *root, BooleanTest *clause, int varRelid)
11791184
}
11801185

11811186
/* result should be in range, but make sure... */
1182-
if (selec<0.0)
1183-
selec=0.0;
1184-
elseif (selec>1.0)
1185-
selec=1.0;
1187+
CLAMP_PROBABILITY(selec);
11861188

11871189
return (Selectivity)selec;
11881190
}
@@ -1285,10 +1287,7 @@ nulltestsel(Query *root, NullTest *clause, int varRelid)
12851287
}
12861288

12871289
/* result should be in range, but make sure... */
1288-
if (selec<0.0)
1289-
selec=0.0;
1290-
elseif (selec>1.0)
1291-
selec=1.0;
1290+
CLAMP_PROBABILITY(selec);
12921291

12931292
return (Selectivity)selec;
12941293
}
@@ -1448,6 +1447,7 @@ eqjoinsel(PG_FUNCTION_ARGS)
14481447
}
14491448
}
14501449
}
1450+
CLAMP_PROBABILITY(matchprodfreq);
14511451
/* Sum up frequencies of matched and unmatched MCVs */
14521452
matchfreq1=unmatchfreq1=0.0;
14531453
for (i=0;i<nvalues1;i++)
@@ -1457,6 +1457,8 @@ eqjoinsel(PG_FUNCTION_ARGS)
14571457
else
14581458
unmatchfreq1+=numbers1[i];
14591459
}
1460+
CLAMP_PROBABILITY(matchfreq1);
1461+
CLAMP_PROBABILITY(unmatchfreq1);
14601462
matchfreq2=unmatchfreq2=0.0;
14611463
for (i=0;i<nvalues2;i++)
14621464
{
@@ -1465,6 +1467,8 @@ eqjoinsel(PG_FUNCTION_ARGS)
14651467
else
14661468
unmatchfreq2+=numbers2[i];
14671469
}
1470+
CLAMP_PROBABILITY(matchfreq2);
1471+
CLAMP_PROBABILITY(unmatchfreq2);
14681472
pfree(hasmatch1);
14691473
pfree(hasmatch2);
14701474

@@ -1474,6 +1478,8 @@ eqjoinsel(PG_FUNCTION_ARGS)
14741478
*/
14751479
otherfreq1=1.0-stats1->stanullfrac-matchfreq1-unmatchfreq1;
14761480
otherfreq2=1.0-stats2->stanullfrac-matchfreq2-unmatchfreq2;
1481+
CLAMP_PROBABILITY(otherfreq1);
1482+
CLAMP_PROBABILITY(otherfreq2);
14771483

14781484
/*
14791485
* We can estimate the total selectivity from the point of
@@ -1544,6 +1550,9 @@ eqjoinsel(PG_FUNCTION_ARGS)
15441550
if (HeapTupleIsValid(statsTuple2))
15451551
ReleaseSysCache(statsTuple2);
15461552
}
1553+
1554+
CLAMP_PROBABILITY(selec);
1555+
15471556
PG_RETURN_FLOAT8((float8)selec);
15481557
}
15491558

@@ -2213,6 +2222,9 @@ convert_timevalue_to_scalar(Datum value, Oid typid)
22132222
*
22142223
* var: identifies the attribute to examine.
22152224
* stats: pg_statistic tuple for attribute, or NULL if not available.
2225+
*
2226+
* NB: be careful to produce an integral result, since callers may compare
2227+
* the result to exact integer counts.
22162228
*/
22172229
staticdouble
22182230
get_att_numdistinct(Query*root,Var*var,Form_pg_statisticstats)
@@ -2254,7 +2266,7 @@ get_att_numdistinct(Query *root, Var *var, Form_pg_statistic stats)
22542266
if (stats->stadistinct>0.0)
22552267
returnstats->stadistinct;
22562268
if (stats->stadistinct<0.0)
2257-
return-stats->stadistinct*ntuples;
2269+
returnfloor((-stats->stadistinct*ntuples)+0.5);
22582270
}
22592271

22602272
/*

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