RE: [HACKERS] Open 6.5 items

> -----Original Message-----
> From: root@sunpine.krs.ru [mailto:root@sunpine.krs.ru]On Behalf Of Vadim
> Mikheev
> Sent: Thursday, June 03, 1999 10:45 PM
> To: Hiroshi Inoue
> Cc: Tom Lane; t-ishii@sra.co.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@tpf.co.jp