On Tue, Dec 5, 2017 at 6:12 AM, Alvaro Herrera <alvherre@xxxxxxxxxxxxxx> wrote: > 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. Something that perhaps does not concern you directly, but in Postgres 11 WAL segments get recycled after one completed checkpoint thanks to commit 4b0d28d. -- Michael
