Rebase done.
Meanwhile I made some more changes.
Changes
=======
1) WAITLSN is now implemented as an extension called "pg_waitlsn"
2) Call new hook "lsn_updated_hook" right after xact_redo_commit (xlog.c)
3) Corresponding functions:
pg_waitlsn('0/693FF800', 10000) - wait 10 seconds
pg_waitlsn_infinite('0/693FF800') - for infinite wait
pg_waitlsn_no_wait('0/693FF800') - once check if LSN was replayed or not.
4) Add two GUCs which help tuning influence on StartupXLOG:
count_waitlsn (denominator to check not each LSN)
int count_waitlsn = 10;
interval_waitlsn (Interval in milliseconds to additional LSN check)
int interval_waitlsn = 100;
5) Optimize loop that set latches.
How to use it
==========
Master:
1) Make "wal_level = replica"
Slave:
2) Add shared_preload_libraries = 'pg_waitlsn'
hot_standby = on (in postgresql.conf)
3) Create extension pg_waitlsn;
4) And in hot_standby you can wait for LSN (pgsleep), when LSN will
replayed on slave pg_waitlsn will release
select pg_waitlsn(‘LSN’ [, timeout in ms]);
select pg_waitlsn_infinite(‘LSN’);
select pg_waitlsn_no_wait(‘LSN’);
#Wait until LSN 0/303EC60 will be replayed, or 10 second passed.
select pg_waitlsn(‘0/303EC60’, 10000);
#Or same without timeout.
select pg_waitlsn(‘0/303EC60’);
select pg_waitlsn_infinite('0/693FF800');
#To check if LSN is replayed can be used.
select pg_waitlsn_no_wait('0/693FF800');
Notice: select pg_waitlsn will release on PostmasterDeath or
Interruption events if they come earlier then target LSN or timeout.
--
Ivan Kartyshov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company
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