RE: [HACKERS] Open 6.5 items

> -----Original Message-----
> From: root(at)sunpine(dot)krs(dot)ru [mailto:root(at)sunpine(dot)krs(dot)ru]On Behalf Of Vadim
> Mikheev
> Sent: Thursday, June 03, 1999 10:45 PM
> To: Hiroshi Inoue
> Cc: Tom Lane; t-ishii(at)sra(dot)co(dot)jp; PostgreSQL-development
> Subject: Re: [HACKERS] Open 6.5 items
>
>
> Hiroshi Inoue wrote:
> >
> > However,when I did vacuum while testing I got the following error
> > message.
> > ERROR: Child itemid marked as unused
> >
> > TransactionId-s of tuples in update chain may be out of order.
>
> 1. Fix and explanation in xact.c:CommitTransaction():
>
> RecordTransactionCommit();
>
> /*
> * Let others know about no transaction in progress by me.
> * Note that this must be done _before_ releasing locks we hold
> * and SpinAcquire(ShmemIndexLock) is required - or bad (too high)
> * XmaxRecent value might be used by vacuum: UPDATE with xid 0 is
> * blocked by xid 1' UPDATE, xid 1 is doing commit while xid 2
> * gets snapshot - if xid 2' GetSnapshotData sees xid 1 as running
> * then it must see xid 0 as running as well or XmaxRecent = 1
> * might be used by concurrent vacuum causing
> * ERROR: Child itemid marked as unused
> * This bug was reported by Hiroshi Inoue and I was able to reproduce
> * it with 3 sessions and gdb. - vadim 06/03/99
> */
> if (MyProc != (PROC *) NULL)
> {
> SpinAcquire(ShmemIndexLock);
> MyProc->xid = InvalidTransactionId;
> MyProc->xmin = InvalidTransactionId;
> SpinRelease(ShmemIndexLock);
> }
>
> 2. It was possible to get two versions of the same row from
> select. Fixed by moving MyProc->xid assignment from
> StartTransaction() inside GetNewTransactionId().
>
> Thanks, Hiroshi! And please run your tests - I used just
> 3 sessions and gdb.
>

Unfortunately,the error still occurs(I changed xact.c as above
by hand OK ?).

It seems there are cases that tuples are updated by older
transactions than their xmin-s and only some tuples in the middle
of update chain may be deleted.

I have no idea to fix this now.
It's OK for me to leave this unsolved because those cases would
rarely occur.

Thanks.

Hiroshi Inoue
Inoue(at)tpf(dot)co(dot)jp