Question

I have an INSERT query in Oracle 10g that is getting stuck on a “SQL*Net message from dblink” event. It looks like:

INSERT INTO my_table (A, B, C, ...) 
  SELECT A, B, C, ... FROM link_table@other_system;

I do not see any locks on my_table besides the one from the INSERT I’m trying to do. The SELECT query on link_table@other_system completes without any trouble when run on its own. I only get this issue when I try to do the INSERT.

Does anyone know what could be going on here?

UPDATE
The SELECT returns 4857 rows in ~1.5 mins when run alone. The INSERT was running over an hour with this wait message before I decided to kill it.

UPDATE
I found an error in my methods. I was using a date range to limit the results. The date range I used when testing the SELECT only was before the last OraStats run on the link_table, but the date range that I used when testing the INSERT was after the last OraStats run on the link_table. So, that mislead me to believe there was a problem with the INSERT. Not very scientific of me to do this; my mistake.

Answer 1

Are you using a /*+ driving_site(link_table) */ hint to make Oracle perform the joins on the remote server?

If so, that hint will not work with DML, as explained by Jonathan Lewis on this page.

This may be a rare case where running the query just as a SELECT uses a very different plan than running the query as part of an INSERT. (You will definitely want to learn how to generate explain plans in your environment. Most tools have a button to do this.)

As Andras Gabor recommended in the link, you may want to use PL/SQL BULK COLLECT to improve performance. This may be a rare case where PL/SQL will work faster than SQL.