![]() ![]() ![]() The standby can be started in various conditions.The start of log-shipping does not interfere with any query processing on the primary.The standby periodically removes old XLOG files which are no longer needed for recovery, to prevent excessive disk usage.The combination of Hot Standby and SR would make the latest data inserted into the primary visible in the standby almost immediately. XLOG records shipped are replayed as soon as possible without waiting until XLOG file has been filled.The standby continuously replays XLOG records shipped without using pg_standby.The maximum number of standbys can be specified as a GUC variable.The delay/death of a standby does not harm log-shipping to other standbys. XLOG records are concurrently shipped to all these standbys. More than one standby can establish a connection to the primary for SR.XLOG files shipped can be used for a normal recovery and PITR. The content of XLOG files written to the standby are exactly the same as those on the primary.This means the window for data loss in SR is usually smaller than in warm standby, unless the warm standby was also configured for record-based shipping (which is complicated to setup). In SR, XLOG records in partially-filled XLOG file are shipped too, implementing record-based log-shipping. In the existing warm standby, only records in a filled file are shipped, what's referred to as file-based log-shipping.XLOG records generated in the primary are periodically shipped to the standby via the network.Synchronous Log Shipping Replication Presentation introduces the early design of the feature. SR was developed for inclusion in PostgreSQL 9.0 by NTT OSS Center. 1 Developer and historical details on the projectÄeveloper and historical details on the project.However, the number returned there is actually the "time since the last replayed transaction from the master" - so if the master hasn't had a transaction in awhile that "time" might make it seem like the slave is falling behind (when it reality, it is caught up, but there have been no transactions on the master. Pg_last_xact_replay_timestamp())) AS time_lag On the slave you can get an idea of the time delay using the query: SELECT extract(epoch from (now(). Of course, if the slave is replaying slowly it might never catch up - but you can measure if it is "catching up" or "falling behind" (sort of) using the query below: Technically it's "possible" for a slave to catch up with the master if the log files that the slave needs are still available on the master. You could locate the current WAL file name in use using: select pg_xlogfile_name(pg_current_xlog_insert_location()) ![]() The part before the "/" is multiplied by 'ff000000' and added to the second part: If you take the output of: SELECT pg_current_xlog_location() you'll get something like: 70/A9002358 The log unit are in bytes (though they are relative - so they aren't useful for measuring anything other than "offsets", and there sometimes can be "jumps" where there's a lot of skipped bytes), with the value being computed as:
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