GIN posting lists are now encoded using varbyte-encoding, which allows them
to fit in much smaller space than the straight ItemPointer array format used
before. The new encoding is used for both the lists stored in-line in entry
tree items, and in posting tree leaf pages.
To maintain backwards-compatibility and keep pg_upgrade working, the code
can still read old-style pages and tuples. Posting tree leaf pages in the
new format are flagged with GIN_COMPRESSED flag, to distinguish old and new
format pages. Likewise, entry tree tuples in the new format have a
GIN_ITUP_COMPRESSED flag set in a bit that was previously unused.
This patch bumps GIN_CURRENT_VERSION from 1 to 2. New indexes created with
version 9.4 will therefore have version number 2 in the metapage, while old
pg_upgraded indexes will have version 1. The code treats them the same, but
it might be come handy in the future, if we want to drop support for the
uncompressed format.
Alexander Korotkov and me. Reviewed by Tomas Vondra and Amit Langote.
This allows us to specify the target relation with several expressions,
'relname', 'schemaname.relname' and OID in all pgstattuple functions.
pgstatindex() and pg_relpages() could not accept OID as the argument
so far.
Per discussion on -hackers, we decided to keep two types of interfaces,
with regclass-type and TEXT-type argument, for each pgstattuple
function because of the backward-compatibility issue. The functions
which have TEXT-type argument will be deprecated in the future release.
Patch by Satoshi Nagayasu, reviewed by Rushabh Lathia and Fujii Masao.
