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Commitcd3dfb0

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Make contrib/btree_gist's GiST penalty function a bit saner.
The previous coding supposed that the first differing bytes in two varlenadatums must have the same sign difference as their overall comparisonresult. This is obviously bogus for text strings in non-C locales, andprobably wrong for numeric, and even for bytea I think it was wrong onmachines where char is signed. When the assumption failed, the functioncould deliver a zero or negative penalty in situations where such a resultis quite ridiculous, leading the core GiST code to make very bad page-splitdecisions.To fix, take the absolute values of the byte-level differences. Also,switch the code to using unsigned char not just char, so that the behaviorwill be consistent whether char is signed or not.Per investigation of a trouble report from Tomas Vondra. Back-patch to allsupported branches.
1 parent500889a commitcd3dfb0

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+10
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‎contrib/btree_gist/btree_utils_var.c

Lines changed: 10 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -106,14 +106,12 @@ gbt_var_leaf2node(GBT_VARKEY *leaf, const gbtree_vinfo *tinfo)
106106
staticint32
107107
gbt_var_node_cp_len(constGBT_VARKEY*node,constgbtree_vinfo*tinfo)
108108
{
109-
110109
GBT_VARKEY_Rr=gbt_var_key_readable(node);
111110
int32i=0;
112111
int32l=0;
113112
int32t1len=VARSIZE(r.lower)-VARHDRSZ;
114113
int32t2len=VARSIZE(r.upper)-VARHDRSZ;
115114
int32ml=Min(t1len,t2len);
116-
117115
char*p1=VARDATA(r.lower);
118116
char*p2=VARDATA(r.upper);
119117

@@ -124,7 +122,6 @@ gbt_var_node_cp_len(const GBT_VARKEY *node, const gbtree_vinfo *tinfo)
124122
{
125123
if (tinfo->eml>1&&l==0)
126124
{
127-
128125
if ((l=pg_mblen(p1))!=pg_mblen(p2))
129126
{
130127
returni;
@@ -367,13 +364,14 @@ gbt_var_penalty(float *res, const GISTENTRY *o, const GISTENTRY *n,
367364
GBT_VARKEY*newe= (GBT_VARKEY*)DatumGetPointer(n->key);
368365
GBT_VARKEY_Rok,
369366
nk;
370-
GBT_VARKEY*tmp=NULL;
371367

372368
*res=0.0;
373369

374370
nk=gbt_var_key_readable(newe);
375371
if (nk.lower==nk.upper)/* leaf */
376372
{
373+
GBT_VARKEY*tmp;
374+
377375
tmp=gbt_var_leaf2node(newe,tinfo);
378376
if (tmp!=newe)
379377
nk=gbt_var_key_readable(tmp);
@@ -388,7 +386,7 @@ gbt_var_penalty(float *res, const GISTENTRY *o, const GISTENTRY *n,
388386
gbt_bytea_pf_match(ok.upper,nk.upper,tinfo))))
389387
{
390388
Datumd=PointerGetDatum(0);
391-
doubledres=0.0;
389+
doubledres;
392390
int32ol,
393391
ul;
394392

@@ -399,20 +397,18 @@ gbt_var_penalty(float *res, const GISTENTRY *o, const GISTENTRY *n,
399397

400398
if (ul<ol)
401399
{
402-
dres= (ol-ul);/*lost of common prefix len */
400+
dres= (ol-ul);/*reduction of common prefix len */
403401
}
404402
else
405403
{
406404
GBT_VARKEY_Ruk=gbt_var_key_readable((GBT_VARKEY*)DatumGetPointer(d));
405+
unsignedchartmp[4];
407406

408-
chartmp[4];
409-
410-
tmp[0]= ((VARSIZE(ok.lower)-VARHDRSZ)==ul) ? (CHAR_MIN) : (VARDATA(ok.lower)[ul]);
411-
tmp[1]= ((VARSIZE(uk.lower)-VARHDRSZ)==ul) ? (CHAR_MIN) : (VARDATA(uk.lower)[ul]);
412-
tmp[2]= ((VARSIZE(ok.upper)-VARHDRSZ)==ul) ? (CHAR_MIN) : (VARDATA(ok.upper)[ul]);
413-
tmp[3]= ((VARSIZE(uk.upper)-VARHDRSZ)==ul) ? (CHAR_MIN) : (VARDATA(uk.upper)[ul]);
414-
dres= (tmp[0]-tmp[1])+
415-
(tmp[3]-tmp[2]);
407+
tmp[0]= (unsignedchar) (((VARSIZE(ok.lower)-VARHDRSZ) <=ul) ?0 : (VARDATA(ok.lower)[ul]));
408+
tmp[1]= (unsignedchar) (((VARSIZE(uk.lower)-VARHDRSZ) <=ul) ?0 : (VARDATA(uk.lower)[ul]));
409+
tmp[2]= (unsignedchar) (((VARSIZE(ok.upper)-VARHDRSZ) <=ul) ?0 : (VARDATA(ok.upper)[ul]));
410+
tmp[3]= (unsignedchar) (((VARSIZE(uk.upper)-VARHDRSZ) <=ul) ?0 : (VARDATA(uk.upper)[ul]));
411+
dres=Abs(tmp[0]-tmp[1])+Abs(tmp[3]-tmp[2]);
416412
dres /=256.0;
417413
}
418414

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