Itai Zukerman wrote:
I didn't get any responses on pgsql-sql, so I'm re-posting here...
Is the GiST examples I've looked through, in the picksplit functions, I see code that looks roughly like this:
bytea *entryvec = (bytea *) PG_GETARG_POINTER(0); OffsetNumber i, maxoff;
maxoff = ((VARSIZE(entryvec) - VARHDRSZ) / sizeof(GISTENTRY)) - 1;
for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i)) { ... DatumGetPointer((((GISTENTRY *) (VARDATA(entryvec)))[i].key)) ... }
I'm wondering, since FirstOffsetNumber is 1, what about the 0'th index in entryvec? Is it just not set?
In backend/access/gist/gist.c I see how entryvec is built:
storage = palloc(MAXALIGN(VARHDRSZ) + (*len + 1) * sizeof(GISTENTRY)); entryvec = (bytea *) (storage + MAXALIGN(VARHDRSZ) - VARHDRSZ); decompvec = (bool *) palloc((*len + 1) * sizeof(bool)); VARATT_SIZEP(entryvec) = (*len + 1) * sizeof(GISTENTRY) + VARHDRSZ; for (i = 1; i <= *len; i++) { [...] gistdentryinit(giststate, 0, &((GISTENTRY *) VARDATA(entryvec))[i], [...] }
So it looks like the 0'th entry indeed is empty. Why?
Also, in gist.c the index "i" has type "int". No mention of OffsetNumber anywhere. Any reason for that?
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