[GENERAL] Re: have trouble understanding xmin and xmax with update operations from two different sessions

2017-07-01 Thread rajan
Thanks, Jeff. That helps understanding it 50%. *Session 2* fails to UPDATE the record which is in *(0,2)* and this tuple is marked for deletion. It means that *(0,2) never exists* when Session 2 is trying to perform the update. In that case, how *Session 3's new row (0,4)* contains the xmax as

Re: [GENERAL] Re: have trouble understanding xmin and xmax with update operations from two different sessions

2017-07-01 Thread Jeff Janes
On Sat, Jul 1, 2017 at 6:32 PM, rajan wrote: > hello, > > thanks for replies, Adrian, Steven. > > >So calling it can advance the xid manually. Some testing here showed > >that what xmin or xmax is created depends on when you call txid_current > >in either the original session

[GENERAL] Re: have trouble understanding xmin and xmax with update operations from two different sessions

2017-07-01 Thread rajan
hello, thanks for replies, Adrian, Steven. >So calling it can advance the xid manually. Some testing here showed >that what xmin or xmax is created depends on when you call txid_current >in either the original session or the concurrent sessions. I understand this and I am executing my

Re: [GENERAL] have trouble understanding xmin and xmax with update operations from two different sessions

2017-07-01 Thread stevenchang1213
this chapter introduces mvcc http://www.interdb.jp/pg/pgsql05.html 原始訊息 自： rajan 日期： 2017/7/1 14:32 (GMT+08:00) 至： pgsql-general@postgresql.org 主旨： [GENERAL] have trouble understanding xmin and xmax with update operations from two different sessions

Re: [GENERAL] have trouble understanding xmin and xmax with update operations from two different sessions

2017-07-01 Thread Adrian Klaver
On 06/30/2017 11:32 PM, rajan wrote: have trouble understanding xmin and xmax with update operations from two different sessions So, as found below, Session2 is trying to update a row which is already updated with a different value and it's update fails with *UPDATE 0* But from Session3, I see

Re: [GENERAL] duplicate key value violates unique constraint and duplicated records

2017-07-01 Thread Melvin Davidson
On Sat, Jul 1, 2017 at 10:05 AM, Adrian Klaver wrote: > On 06/30/2017 09:42 PM, Steven Chang wrote: > >> Uh...we also met duplicate rows with primary key column through >> restoring database by pg_basebackup. >> H. >> I don't think its an

Re: [GENERAL] duplicate key value violates unique constraint and duplicated records

2017-07-01 Thread Adrian Klaver
On 06/30/2017 09:42 PM, Steven Chang wrote: Uh...we also met duplicate rows with primary key column through restoring database by pg_basebackup. H. I don't think its an issue with primary key index corruption. That is interesting, more information would be

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[GENERAL] have trouble understanding xmin and xmax with update operations from two different sessions

2017-07-01 Thread rajan
have trouble understanding xmin and xmax with update operations from two different sessions So, as found below, Session2 is trying to update a row which is already updated with a different value and it's update fails with *UPDATE 0* But from Session3, I see that xmax value is visible as