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Fix confusion in SP-GiST between attribute type and leaf storage type.

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According to the documentation, the attType passed to the opclass
config function (and also relied on by the core code) is the type
of the heap column or expression being indexed.  But what was
actually being passed was the type stored for the index column.
This made no difference for user-defined SP-GiST opclasses,
because we weren't allowing the STORAGE clause of CREATE OPCLASS
to be used, so the two types would be the same.  But it's silly
not to allow that, seeing that the built-in poly_ops opclass
has a different value for opckeytype than opcintype, and that if you
want to do lossy storage then the types must really be different.
(Thus, user-defined opclasses doing lossy storage had to lie about
what type is in the index.)  Hence, remove the restriction, and make
sure that we use the input column type not opckeytype where relevant.

For reasons of backwards compatibility with existing user-defined
opclasses, we can't quite insist that the specified leafType match
the STORAGE clause; instead just add an amvalidate() warning if
they don't match.

Also fix some bugs that would only manifest when trying to return
index entries when attType is different from attLeafType.  It's not
too surprising that these have not been reported, because the only
usual reason for such a difference is to store the leaf value
lossily, rendering index-only scans impossible.

Add a src/test/modules module to exercise cases where attType is
different from attLeafType and yet index-only scan is supported.

Discussion: https://postgr.es/m/3728741.1617381471@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2021-04-04 14:28:35 -04:00
parent d9c5b9a9ee
commit ac9099fc1d
17 changed files with 937 additions and 44 deletions
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6
src/include/access/spgist_private.h
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@@ -151,8 +151,8 @@ typedef struct SpGistState
typedef struct SpGistSearchItem
{
pairingheap_node phNode; /* pairing heap node */
Datum value; /* value reconstructed from parent or
* leafValue if heaptuple */
Datum value; /* value reconstructed from parent, or
* leafValue if isLeaf */
void *traversalValue; /* opclass-specific traverse value */
int level; /* level of items on this page */
ItemPointerData heapPtr; /* heap info, if heap tuple */
@@ -208,7 +208,7 @@ typedef struct SpGistScanOpaqueData
/* These fields are only used in amgettuple scans: */
bool want_itup; /* are we reconstructing tuples? */
TupleDesc indexTupDesc; /* if so, tuple descriptor for them */
TupleDesc indexTupDesc; /* if so, descriptor for reconstructed tuples */
int nPtrs; /* number of TIDs found on current page */
int iPtr; /* index for scanning through same */
ItemPointerData heapPtrs[MaxIndexTuplesPerPage]; /* TIDs from cur page */