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Commitd5890f4

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Fix hstore hash function for empty hstores upgraded from 8.4.
Hstore data generated on pg 8.4 and pg_upgraded to current versionsremains in its original on-disk format unless modified. The same goesfor values generated by the addon hstore-new module on pre-9.0versions. (The hstoreUpgrade function converts old values on the flywhen read in, but the on-disk value is not modified by this.)Since old-format empty hstores (and hstore-new hstores) haverepresentations compatible with the new format, hstoreUpgrade thoughtit could get away without modifying such values; but this breakshstore_hash (and the new hstore_hash_extended) which assumesbit-perfect matching between semantically identical hstore values.Only one bit actually differs (the "new version" flag in the countfield) but that of course is enough to break the hash.Fix by making hstoreUpgrade unconditionally convert all old values tonew format.Backpatch all the way, even though this changes a hash value in somecases, because in those cases the hash value is already failing - forexample, a hash join between old- and new-format empty hstores will befailing to match, or a hash index on an hstore column containing anold-format empty value will be failing to find the value since it willbe searching for a hash derived from a new-format datum. (There are noknown field reports of this happening, probably because hashing ofhstores has only been useful in limited circumstances and thereprobably isn't much upgraded data being used this way.)Per concerns arising from discussion of commiteb6f291. Originalbug is my fault.Discussion:https://postgr.es/m/60b1fd3b-7332-40f0-7e7f-f2f04f777747%402ndquadrant.com
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‎contrib/hstore/hstore_compat.c

Lines changed: 19 additions & 28 deletions
Original file line numberDiff line numberDiff line change
@@ -238,34 +238,35 @@ hstoreUpgrade(Datum orig)
238238
HStore*hs= (HStore*)PG_DETOAST_DATUM(orig);
239239
intvalid_new;
240240
intvalid_old;
241-
boolwritable;
242241

243242
/* Return immediately if no conversion needed */
244-
if ((hs->size_&HS_FLAG_NEWVERSION)||
245-
hs->size_==0||
243+
if (hs->size_&HS_FLAG_NEWVERSION)
244+
returnhs;
245+
246+
/* Do we have a writable copy? If not, make one. */
247+
if ((void*)hs== (void*)DatumGetPointer(orig))
248+
hs= (HStore*)PG_DETOAST_DATUM_COPY(orig);
249+
250+
if (hs->size_==0||
246251
(VARSIZE(hs)<32768&&HSE_ISFIRST((ARRPTR(hs)[0]))))
252+
{
253+
HS_SETCOUNT(hs,HS_COUNT(hs));
254+
HS_FIXSIZE(hs,HS_COUNT(hs));
247255
returnhs;
256+
}
248257

249258
valid_new=hstoreValidNewFormat(hs);
250259
valid_old=hstoreValidOldFormat(hs);
251-
/* Do we have a writable copy? */
252-
writable= ((void*)hs!= (void*)DatumGetPointer(orig));
253260

254261
if (!valid_old||hs->size_==0)
255262
{
256263
if (valid_new)
257264
{
258265
/*
259-
* force the "new version" flag and the correct varlena length,
260-
* but only if we have a writable copy already (which we almost
261-
* always will, since short new-format values won't come through
262-
* here)
266+
* force the "new version" flag and the correct varlena length.
263267
*/
264-
if (writable)
265-
{
266-
HS_SETCOUNT(hs,HS_COUNT(hs));
267-
HS_FIXSIZE(hs,HS_COUNT(hs));
268-
}
268+
HS_SETCOUNT(hs,HS_COUNT(hs));
269+
HS_FIXSIZE(hs,HS_COUNT(hs));
269270
returnhs;
270271
}
271272
else
@@ -302,29 +303,19 @@ hstoreUpgrade(Datum orig)
302303
elog(WARNING,"ambiguous hstore value resolved as hstore-new");
303304

304305
/*
305-
* force the "new version" flag and the correct varlena length, but
306-
* only if we have a writable copy already (which we almost always
307-
* will, since short new-format values won't come through here)
306+
* force the "new version" flag and the correct varlena length.
308307
*/
309-
if (writable)
310-
{
311-
HS_SETCOUNT(hs,HS_COUNT(hs));
312-
HS_FIXSIZE(hs,HS_COUNT(hs));
313-
}
308+
HS_SETCOUNT(hs,HS_COUNT(hs));
309+
HS_FIXSIZE(hs,HS_COUNT(hs));
314310
returnhs;
315311
#else
316312
elog(WARNING,"ambiguous hstore value resolved as hstore-old");
317313
#endif
318314
}
319315

320316
/*
321-
* must have an old-style value. Overwrite it in place as a new-style one,
322-
* making sure we have a writable copy first.
317+
* must have an old-style value. Overwrite it in place as a new-style one.
323318
*/
324-
325-
if (!writable)
326-
hs= (HStore*)PG_DETOAST_DATUM_COPY(orig);
327-
328319
{
329320
intcount=hs->size_;
330321
HEntry*new_entries=ARRPTR(hs);

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