I have two questions/suggestions about replication lag check for straming
replication in pgpool-II.
1. In text_to_lsn() there is formula
lsn = xlogid * 16 * 1024 * 1024 * 255 + xrecoff;
16 * 1024 * 1024 * 255 = 4278190080 = 0xff000000
where this magic numbers come from?
I think multiplier should be
0xffffffff - XLogSegSize.
In PostgreeSQL source this constant used in
src/include/access/xlog_internal.h
#define XLogSegsPerFile (((uint32) 0xffffffff) / XLogSegSize)
But in comment noted, that one segment at the end of each log file is wasted
Each xlogid corresponds to (XLogSegsPerFile - 1) * XLogSegSize = 0xffffffff -
XLogSegSize bytes
2. On slave better to use
SELECT pg_last_xlog_replay_location()
instead
SELECT pg_last_xlog_receive_location()
if we want to know if slave will return stale data on SELECTs to user's
databases.
--
Anton Yuzhaninov
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