From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
Cc: | Martijn van Oosterhout <kleptog(at)svana(dot)org>, Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: Unsplitting btree index leaf pages |
Date: | 2005-12-22 20:11:28 |
Message-ID: | 26260.1135282288@sss.pgh.pa.us |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-hackers |
Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> We already do something similar for page deletions. Empty pages are not
> deleted right away, but they are marked with BTP_DEAD, and then deleted
> on a subsequent vacuum. Or something like that, I don't remember the
> exact details.
Right, and the reason for that is exactly that there might be a
concurrent indexscan already "in flight" to the newly-dead page.
We must wait to recycle the page until we are certain no such scans
remain.
It doesn't matter whether a concurrent indexscan visits the dead
page or not, *because it's empty* and so there's nothing to miss.
So there's no race condition. But if you try to move valid data
across pages then there is a race condition.
regards, tom lane
From | Date | Subject | |
---|---|---|---|
Next Message | Bruce Momjian | 2005-12-22 20:14:09 | Re: Automatic function replanning |
Previous Message | Simon Riggs | 2005-12-22 20:10:54 | Re: WAL bypass for INSERT, UPDATE and DELETE? |