Re: [HACKERS] Use of snapshot in logical replication
On 2017-06-08 03:14:55 +0200, Petr Jelinek wrote: > On 08/06/17 03:08, Craig Ringer wrote: > > On 7 June 2017 at 18:16, sanyam jainwrote: > >> Hi, > >> > >> Can someone explain the usage of exporting snapshot when a logical > >> replication slot is created? > > > > It's used to pg_dump the schema at a consistent point in history where > > all xacts are known to be in the snapshot (and thus dumped) or known > > not to be (so they'll be streamed out on the slot). > > > > Not just schema, it can also be used to get existing data at consistent > point in history so that changes will follow without gaps or duplicates. > > That being said, the built-in logical replication isn't using the > exported snapshots at all. Just because it uses them in the same session doesn't really change the picture, that's more or less just an optimization. It's essentially just a cheaper version of importing a snapshot that'd have to be exported in same session. - Andres -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Use of snapshot in logical replication
On 08/06/17 03:08, Craig Ringer wrote: > On 7 June 2017 at 18:16, sanyam jainwrote: >> Hi, >> >> Can someone explain the usage of exporting snapshot when a logical >> replication slot is created? > > It's used to pg_dump the schema at a consistent point in history where > all xacts are known to be in the snapshot (and thus dumped) or known > not to be (so they'll be streamed out on the slot). > Not just schema, it can also be used to get existing data at consistent point in history so that changes will follow without gaps or duplicates. That being said, the built-in logical replication isn't using the exported snapshots at all. -- Petr Jelinek http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Use of snapshot in logical replication
On 7 June 2017 at 18:16, sanyam jainwrote: > Hi, > > Can someone explain the usage of exporting snapshot when a logical > replication slot is created? It's used to pg_dump the schema at a consistent point in history where all xacts are known to be in the snapshot (and thus dumped) or known not to be (so they'll be streamed out on the slot). See snapbuild.c etc. -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
[HACKERS] Use of snapshot in logical replication
Hi, Can someone explain the usage of exporting snapshot when a logical replication slot is created? Thanks, Sanyam Jain