Fix unexpected reversal of lists during catcache rehash

During catcache searches, the most-recently searched entries are kept at
the head of the list to speed up subsequent searches, keeping the
"freshest" entries at its beginning.  A rehash of the catcache was doing
the opposite: fresh entries were moved to the tail of the newly-created
buckets, causing a rehash to slow down a bit.

When a rehash is done, this commit switches the code to use
dlist_push_tail() instead of dlist_push_head(), so as fresh entries are
kept at the head of the lists, not their tail.

Author: ChangAo Chen <[email protected]>
Reviewed-by: John Naylor <[email protected]>
Reviewed-by: Michael Paquier <[email protected]>
Discussion: 
https://postgr.es/m/[email protected]

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/68119480a763d761a9cf2413f4320d9a5d4b34d5

Modified Files
--------------
src/backend/utils/cache/catcache.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

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