pgsql: Refactor XLogInsert a bit. The rdata entries for backup blocks a

Refactor XLogInsert a bit. The rdata entries for backup blocks are now
constructed before acquiring WALInsertLock, which slightly reduces the time
the lock is held. Although I could not measure any benefit in benchmarks,
the code is more readable this way.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/9c808f89c2841dd847555898a8db45fcd69e913b

Modified Files
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src/backend/access/transam/xlog.c |  202 +++++++++++++++++--------------------
1 files changed, 91 insertions(+), 111 deletions(-)