Re: [Postgres-xc-developers] Regarding bug id 3607975

[Ashutosh B. <ash...@en...>]

On Thu, May 23, 2013 at 9:21 PM, Abbas Butt <abb...@en...>wrote:

> Hi,
>
> While working on test case plancache it was brought up as a review comment
> that solving bug id 3607975 should solve the problem of the test case.
> However there is some confusion in the statement of bug id 3607975.
>
> "When a user does and PREPARE and then EXECUTEs multiple times, the
> coordinator keeps on preparing and executing the query on datanode al
> times, as against preparing once and executing multiple times. This is
> because somehow the remote query is being prepared as an unnamed statement."
>
> Consider this test case
>
> A. create table abc(a int, b int);
> B. insert into abc values(11, 22);
> C. prepare p1 as select * from abc;
> D. execute p1;
> E. execute p1;
> F. execute p1;
>
> Here are the confusions
>
> 1. The coordinator never prepares on datanode in response to a prepare
> issued by a user.
>      In fact step C does nothing on the datanodes.
>      Step D simply sends "SELECT a, b FROM abc" to all datanodes.
>
> 2. In step D, ExecuteQuery calls BuildCachedPlan to build a new generic
> plan,
>     and steps E and F use the already built generic plan.
>     For details see function GetCachedPlan.
>     This means that executing a prepared statement again and again does
> use cached plans
>     and does not prepare again and again every time we issue an execute.
>
>
The problem is not here. The problem is in do_query() where somehow the
name of prepared statement gets wiped out and we keep on preparing unnamed
statements at the datanode.


> My conclusion is that the bug ID 3607975 is not reproducible.
>
>
Did you verify it under the debugger? If that would have been the case, we
would not have seen this problem if search_path changed in between steps D
and E.


> Comments are welcome.
>
> --
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-- 
Best Wishes,
Ashutosh Bapat
EntepriseDB Corporation
The Postgres Database Company