Re: [COMMITTERS] pgsql: Augment WAL records for btree delete with GetOldestXmin() to
От | Simon Riggs |
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Тема | Re: [COMMITTERS] pgsql: Augment WAL records for btree delete with GetOldestXmin() to |
Дата | |
Msg-id | 1269718607.3684.1967.camel@ebony обсуждение исходный текст |
Ответ на | Re: [COMMITTERS] pgsql: Augment WAL records for btree delete with GetOldestXmin() to (Greg Stark <gsstark@mit.edu>) |
Ответы |
Re: [COMMITTERS] pgsql: Augment WAL records for btree delete with
GetOldestXmin() to
|
Список | pgsql-hackers |
On Sat, 2010-03-27 at 19:15 +0000, Greg Stark wrote: > On Sat, Mar 27, 2010 at 10:10 AM, Simon Riggs <simon@2ndquadrant.com> wrote: > > It appears that in practice many of the index items point to heap items > > that are LP_DEAD. So for the purposes of accessing a heap tuple's xmin, > > then we're both right. To the current purpose the tuple has been > > removed, though you are also right: its stub remains. > > If we're pruning an index entry to a heap tuple that has been HOT > pruned wouldn't the HOT pruning record have already conflicted with > any queries that could see it? Quite probably, but a query that started after that record arrived might slip through. We have to treat each WAL record separately. Do you agree with the conjecture? That LP_DEAD items can be ignored because their xid would have been earlier than the latest LP_NORMAL tuple we find? (on any page). Or is a slightly less strong condition true: we can ignore LP_DEAD items on a page that is also referenced by an LP_NORMAL item. -- Simon Riggs www.2ndQuadrant.com
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