On Tue, Feb 28, 2017 at 1:56 PM, Higuchi, Daisuke <higuchi.dais...@jp.fujitsu.com> wrote: > Hi all, > > I create POC patch for my proposal of new feature for high availability. > I want to discuss about this feature. But this feature might be PG11 > because discussion is not enough. > > This patch enables walsender for async to wait until walsender for sync > confirm > WAL is flashed to Disk. This feature is activated when GUC parameter > "async_walsender_delay" is set on. > > I write the case when this feature is useful (this is the same as I wrote > before): > 1. Primary and synchronous standby are in the same center; called main center. > 2. Asynchronous standby is in the another center; called backup center. > (The backup center is located far away from the main center. If replication > mode is synchronous, performance will be deteriorated. So, this replication > must be Asynchronous. ) > 3. Asynchronous replication is performed in the backup center too. > 4. When primary in main center abnormally stops, standby in main center is > promoted, and the standby in backup center connects to the new primary. > > [Main center] > |--------------------------------------------| > | |----------| synchronous |----------| | > | | | replication | | | > | | primary | <--------------> | standby1 | | > | |----------| |----------| | > |----||--------------------------------------| > || > || asynchronous > || replication > || > || [Backup center] > |----||--------------------------------------| > | |----------| asynchronous |----------| | > | | | replication | | | > | | standby2 | <--------------> | standby3 | | > | |----------| |----------| | > |--------------------------------------------| > > When the load in the main center becomes high, although WAL reaches standby in > backup center, WAL may not reach synchronous standby in main center for > various > reasons. In other words, standby in the backup center may advance beyond > synchronous standby in main center. > > When the primary abnormally stops and standby in main center promotes, two > standbys in backup center must be recovered by pg_rewind. However, it is > necessary to stop new primary for pg_rewind. If pg_basebackup is used, > recovery of backup center takes some times. This is not high availability. >
If the standby server in main center promoted to the new primary server, why do we need to stop it in order to execute pg_rewind to the standbys on backup center? I guess you don't need to stop the new primary server by using --source-server option. Regards, -- Masahiko Sawada NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
