Re: WAL reducing size - Mailing list pgsql-general

From Alvaro Herrera
Subject Re: WAL reducing size
Date
Msg-id 20171204211250.ljsaxf2jhedjjerj@alvherre.pgsql
Whole thread Raw
In response to Re: WAL reducing size  (sql2pg <sekhar.career@gmail.com>)
Responses Re: WAL reducing size
List pgsql-general
sql2pg wrote:
> how about uncommitted(open transactions) .  if a segment has 1 committed and
> 2 uncommitted transactions then will it keep the segment instead deleting it
> after checkpoint , since it has 2 uncommitted transactions 

There is no connection between transaction commit and checkpoint
removing WAL files.  WAL files are removed after two checkpoints have
occured, regardless of transactions that might be open.  The on-disk
effects of those transactions that occured before the earlier checkpoint
are already on disk anyway.  The commit record might appear at whatever
point in the future, and the rows will not become visible to other
transactions until then, regardless of what happened to the WAL
segments.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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