Re: query from sql server linked server slow

Bob,

The core of your question is: " why is statement X parsed (and then executed) differently when issued from connection A or B". If there is still a valid plan in SGA, but not used by other session, there must be a reason.
I'd start checking V$SQL_OPTIMIZER_ENV
what's the reason for the different plans. I'm not sure if that's sufficient, but it should help as a starting point.

My private, pure unscientific guess would be different collation settings which drives some indexes useless. But please don't follow my guesswork. Go for facts.

Hth,
 Martin

Am Mi., 26. Dez. 2018, 19:48 hat Stauffer, Bob <RStauffer_at_fult.com> geschrieben:

> Hi all,
>
>
>
> Oracle 12.2, Red Hat 7, SQL Server 2012
>
>
>
> I know, this isn’t a SQL Server forum, but I’m running out of ideas on how
> to troubleshoot the following. When running a specific query from SQL
> Developer or SQLPlus on my Windows 7 PC in and Oracle database, that query
> is relatively fast. It returns 16 records in less than 20 seconds. But
> when run in a SQL Server instance using SSMS and using OPENQUERYlinked
> server, it never completes – it will actually run for days if we don’t kill
> it. I’ve tracked it down to a difference in execution plans on the Oracle
> database side. Of course, when run in the Oracle database using SQL
> Developer, it generates an efficient execution plan. But when run via
> OPENQUERY/linked server in SQL Server, the execution plan in Oracle is
> horrendous. I’ve tried loading a better plan for the query using
> dbms_spm.alter_sql_plan_baseline, etc., but it ignores the new plan. And
> I’ve tried creating a view for the query, but that makes no difference
> either.
>
>
>
> First, can anyone explain why 2 different execution plans are used in the
> Oracle db for the same query? Supposedly OPENQUERY/linked server are just
> submitting the query to Oracle for optimization without doing any
> “pre-optimization”. And any thoughts on how I can troubleshoot/figure out
> how to fix or get around the problem?
>
>
>
> Thanks much.
>
>
>
> *Bob Stauffer*
>
> rstauffer_at_fult.com
>
>
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