pgsql: When xlogreader asks the callback function to read a page, make

When xlogreader asks the callback function to read a page, make sure we
get a large enough part of the page to include the beginning of the next
record we're interested in. The XLogPageRead callback uses the requested
length to decide which timeline to stream WAL from, and if the first call
is short, and the page contains a timeline switch, we'll repeatedly try
to stream that page from the old timeline, and never get across the
timeline switch.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/88228e6f1d26619756281c508212498f1de1eff5

Modified Files
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src/backend/access/transam/xlogreader.c |   30 ++++++++++++------------------
1 files changed, 12 insertions(+), 18 deletions(-)