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nbtree: Demote minus infinity "can't happen" error. 

Only a very basic logic bug in a _bt_insertonpg() caller could lead to a
violation of this invariant.  Besides, any newitemoff used for an
internal page is sanitized using other "can't happen" errors in
_bt_getstackbuf() or its callers, before _bt_insertonpg() even gets
called.

Also, move the error/assertion from the insert-without-split path of
_bt_insertonpg() to the top of the same function.  There is no reason
why this invariant only applies to insertions that happen to not result
in a page split; cover every insertion.  The assertion naturally belongs
next to the existing generic assertions that document relatively
high-level invariants for the item being inserted.
This commit is contained in:
Peter Geoghegan 2020-03-10 14:15:41 -07:00
parent cacef17223
commit d1e241c226
1 changed files with 8 additions and 12 deletions
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20
src/backend/access/nbtree/nbtinsert.c
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@ -1082,6 +1082,14 @@ _bt_insertonpg(Relation rel,
IndexRelationGetNumberOfKeyAttributes(rel));
Assert(!BTreeTupleIsPosting(itup));
/*
* Every internal page should have exactly one negative infinity item at
* all times. Only _bt_split() and _bt_newroot() should add items that
* become negative infinity items through truncation, since they're the
* only routines that allocate new internal pages.
*/
Assert(P_ISLEAF(lpageop) || newitemoff > P_FIRSTDATAKEY(lpageop));
/* The caller should've finished any incomplete splits already. */
if (P_INCOMPLETE_SPLIT(lpageop))
elog(ERROR, "cannot insert to incompletely split page %u",
@ -1212,18 +1220,6 @@ _bt_insertonpg(Relation rel,
}
}
/*
* Every internal page should have exactly one negative infinity item
* at all times. Only _bt_split() and _bt_newroot() should add items
* that become negative infinity items through truncation, since
* they're the only routines that allocate new internal pages. Do not
* allow a retail insertion of a new item at the negative infinity
* offset.
*/
if (!P_ISLEAF(lpageop) && newitemoff == P_FIRSTDATAKEY(lpageop))
elog(ERROR, "cannot insert second negative infinity item in block %u of index \"%s\"",
itup_blkno, RelationGetRelationName(rel));
/* Do the update. No ereport(ERROR) until changes are logged */
START_CRIT_SECTION();