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Commitf504baa

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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 parent45b315e commitf504baa

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+10
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1 file changed

+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
@@ -92,14 +92,12 @@ gbt_var_leaf2node(GBT_VARKEY *leaf, const gbtree_vinfo *tinfo)
9292
staticint32
9393
gbt_var_node_cp_len(constGBT_VARKEY*node,constgbtree_vinfo*tinfo)
9494
{
95-
9695
GBT_VARKEY_Rr=gbt_var_key_readable(node);
9796
int32i=0;
9897
int32l=0;
9998
int32t1len=VARSIZE(r.lower)-VARHDRSZ;
10099
int32t2len=VARSIZE(r.upper)-VARHDRSZ;
101100
int32ml=Min(t1len,t2len);
102-
103101
char*p1=VARDATA(r.lower);
104102
char*p2=VARDATA(r.upper);
105103

@@ -110,7 +108,6 @@ gbt_var_node_cp_len(const GBT_VARKEY *node, const gbtree_vinfo *tinfo)
110108
{
111109
if (tinfo->eml>1&&l==0)
112110
{
113-
114111
if ((l=pg_mblen(p1))!=pg_mblen(p2))
115112
{
116113
returni;
@@ -378,13 +375,14 @@ gbt_var_penalty(float *res, const GISTENTRY *o, const GISTENTRY *n, const gbtree
378375
GBT_VARKEY*newe= (GBT_VARKEY*)DatumGetPointer(n->key);
379376
GBT_VARKEY_Rok,
380377
nk;
381-
GBT_VARKEY*tmp=NULL;
382378

383379
*res=0.0;
384380

385381
nk=gbt_var_key_readable(newe);
386382
if (nk.lower==nk.upper)/* leaf */
387383
{
384+
GBT_VARKEY*tmp;
385+
388386
tmp=gbt_var_leaf2node(newe,tinfo);
389387
if (tmp!=newe)
390388
nk=gbt_var_key_readable(tmp);
@@ -401,7 +399,7 @@ gbt_var_penalty(float *res, const GISTENTRY *o, const GISTENTRY *n, const gbtree
401399
))
402400
{
403401
Datumd=PointerGetDatum(0);
404-
doubledres=0.0;
402+
doubledres;
405403
int32ol,
406404
ul;
407405

@@ -412,20 +410,18 @@ gbt_var_penalty(float *res, const GISTENTRY *o, const GISTENTRY *n, const gbtree
412410

413411
if (ul<ol)
414412
{
415-
dres= (ol-ul);/*lost of common prefix len */
413+
dres= (ol-ul);/*reduction of common prefix len */
416414
}
417415
else
418416
{
419417
GBT_VARKEY_Ruk=gbt_var_key_readable((GBT_VARKEY*)DatumGetPointer(d));
418+
unsignedchartmp[4];
420419

421-
chartmp[4];
422-
423-
tmp[0]= ((VARSIZE(ok.lower)-VARHDRSZ)==ul) ? (CHAR_MIN) : (VARDATA(ok.lower)[ul]);
424-
tmp[1]= ((VARSIZE(uk.lower)-VARHDRSZ)==ul) ? (CHAR_MIN) : (VARDATA(uk.lower)[ul]);
425-
tmp[2]= ((VARSIZE(ok.upper)-VARHDRSZ)==ul) ? (CHAR_MIN) : (VARDATA(ok.upper)[ul]);
426-
tmp[3]= ((VARSIZE(uk.upper)-VARHDRSZ)==ul) ? (CHAR_MIN) : (VARDATA(uk.upper)[ul]);
427-
dres= (tmp[0]-tmp[1])+
428-
(tmp[3]-tmp[2]);
420+
tmp[0]= (unsignedchar) (((VARSIZE(ok.lower)-VARHDRSZ) <=ul) ?0 : (VARDATA(ok.lower)[ul]));
421+
tmp[1]= (unsignedchar) (((VARSIZE(uk.lower)-VARHDRSZ) <=ul) ?0 : (VARDATA(uk.lower)[ul]));
422+
tmp[2]= (unsignedchar) (((VARSIZE(ok.upper)-VARHDRSZ) <=ul) ?0 : (VARDATA(ok.upper)[ul]));
423+
tmp[3]= (unsignedchar) (((VARSIZE(uk.upper)-VARHDRSZ) <=ul) ?0 : (VARDATA(uk.upper)[ul]));
424+
dres=Abs(tmp[0]-tmp[1])+Abs(tmp[3]-tmp[2]);
429425
dres /=256.0;
430426
}
431427

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