[pgpool-hackers: 4105] Re: Proposal: allow to specify replication delay by time

[Tatsuo Ishii]

> Currently delay_threshold specifies replication delay upper limit in
> bytes. It will be more intuitive to specify the replication delay by
> time like '10 seconds'. For this purpose, we can use
> (pg_last_committed_xact()).timestamp instead of pg_current_wal_lsn(),
> and pg_last_xact_replay_timestamp() instead of
> pg_last_wal_replay_lsn(). One thing we need to care about is, to use
> pg_last_committed_xact(), track_commit_timestamp (available in
> PostgreSQL 9.5 or after) must be enabled. If this is not enabled,
> pg_last_committed_xact() raises an error. Also the function returns
> NULL if no transaction is committed since the system started.
> 
> Comments and/or suggestions are welcome.

I have created a patch for this.

- new config parameter delay_threshold_by_time is added. Number in
  seconds can be specified. If it's greater than 0, replication_delay
  in "show pool_nodes" is presented in seconds with 6 digits after the
  decimal point.

- In order to make the parameter effective, following conditions must be all met:

  - PostgreSQL 9.5 or after
  - track_commit_timestamp is enabled in postgresql.conf

  If not, falls back as if delay_threshold_by_time is 0.

Comments and suggestions are welcome/

Best reagards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp
-------------- next part --------------
A non-text attachment was scrubbed...
Name: replication_delay_by_time.patch
Type: text/x-patch
Size: 12055 bytes
Desc: not available
URL: <http://www.pgpool.net/pipermail/pgpool-hackers/attachments/20220124/773a767c/attachment.bin>