Re: [Postgres-xc-general] JDBC driver for 0.9.4

[Michael P. <mic...@gm...>]

On Mon, Jun 6, 2011 at 9:39 PM, Lionel Frachon <lio...@gm...>wrote:

> Hello,
>
> looking at the debug1 mode log on datanode3, I found some interesting
> points hereafter (vacuum on, max_prepared_transactions=5000):
>
> (with normal inserts)
> [....]
> DEBUG:  unset snapshot info
> DEBUG:  global snapshot info: gxmin: 101, gxmax: 101, gxcnt: 0
> DEBUG:  unset snapshot info
> DEBUG:  global snapshot info: gxmin: 101, gxmax: 101, gxcnt: 0
> DEBUG:  unset snapshot info
> DEBUG:  [re]setting xid = 0, old_value = 0
> DEBUG:  unset snapshot info
> DEBUG:  Received new gxid 102
> DEBUG:  [re]setting xid = 102, old_value = 0
> DEBUG:  TransactionId = 102
> DEBUG:  xid (102) does not follow ShmemVariableCache->nextXid (665)
> DEBUG:  Record transaction commit 101
> DEBUG:  Record transaction commit 102
> DEBUG:  [re]setting xid = 0, old_value = 0
> DEBUG:  unset snapshot info
> DEBUG:  Received new gxid 103
> DEBUG:  [re]setting xid = 103, old_value = 0
> DEBUG:  unset snapshot info
> DEBUG:  global snapshot info: gxmin: 103, gxmax: 103, gxcnt: 0
> DEBUG:  TransactionId = 103
> DEBUG:  xid (103) does not follow ShmemVariableCache->nextXid (665)
> DEBUG:  unset snapshot info
> DEBUG:  global snapshot info: gxmin: 103, gxmax: 103, gxcnt: 0
>
> While inserting with dsitrubuted hashed keys :
>
> [...]
> DEBUG:  [re]setting xid = 0, old_value = 0
> DEBUG:  unset snapshot info
> DEBUG:  Received new gxid 522
> DEBUG:  [re]setting xid = 522, old_value = 0
> DEBUG:  TransactionId = 522
> DEBUG:  xid (522) does not follow ShmemVariableCache->nextXid (665)
> DEBUG:  Record transaction commit 521
> DEBUG:  Record transaction commit 522
> DEBUG:  [re]setting xid = 0, old_value = 0
> DEBUG:  unset snapshot info
> DEBUG:  Received new gxid 524
> DEBUG:  [re]setting xid = 524, old_value = 0
> ERROR:  prepared transaction with identifier "T523" does not exist
> STATEMENT:  COMMIT PREPARED 'T523'
> DEBUG:  [re]setting xid = 0, old_value = 524
> DEBUG:  unset snapshot info
> DEBUG:  Received new gxid 526
> DEBUG:  [re]setting xid = 526, old_value = 0
> ERROR:  prepared transaction with identifier "T525" does not exist
> STATEMENT:  COMMIT PREPARED 'T525'
> DEBUG:  [re]setting xid = 0, old_value = 526
> DEBUG:  unset snapshot info
> DEBUG:  Received new gxid 528
> DEBUG:  [re]setting xid = 528, old_value = 0
> ERROR:  prepared transaction with identifier "T527" does not exist
> [...]
>
You are right.
But this log:
DEBUG:  Received new gxid 103
means that GTM is feeding cluster in transaction ID to a very low value.
This may lead to visibility problems.
You should start GTM with an option like -x 1000 to be sure that it doesn't
feed transaction IDs lower than 628.
-- 
Michael Paquier
http://michael.otacoo.com