Archive for August 11th, 2008
I’ve been following a number of threads on forums.oracle.com recently – the quality of discussion seems to have improved markedly there since I gave up on it in 2001. Anyway there was a thread about interpreting the AWR report that Oracle provides (at extra cost) and which is very smilar to the Statspack report. The report in question comes from a siebel system and there were some interesting snippets of information from Joe Coffey about the specifics of working with SIEBEL which would likely trap the unwary (like me) when using sqlplus to investigate an application performance problem. The specifics are in this post but are that siebel specifically alters the standard oracle environment on login with 4 ALTER SESSION statements – namely
alter session set optimizer_mode = first_rows_10;
alter session set hash_join_enabled = false;
alter session set "_optimizer_sortmerge_join_enabled" = false;
alter session set "_optimizer_join_sel_sanity_check" = true;
Now first_rows_10 is rather sensible for a reporting application where the end user is going to look at pages of results – I’m rather less convinced about the wisdom of avoiding hash_joins and sortmerge joins altogether, but the base point to remember here – for myself as much as any reader – is that when conducting tests using sqlplus (or toad or any other query environment ) it matters that you ensure that your session mimics effectively the one the users will be using.