ids 11.70.fc3 read ahead
Aix 6.1 Prior to moving to the above version we had read ahead set to 1024 and 512 ... When we came up on 11.70.fc3, we turned on the AUTO_READAHEAD. 4 days later started crashing, so after working with Tech Support we switched back to using RA_PAGES and turning off AUTO_READAHEAD. Now our performance seems to be severely impacted. Has anyone else had any negative impact with this? Thanks Peter Logan Senior Database Administrator Phone: 616/878-8309
Why did tech support think that AUTO_READAHEAD was the cause? From: "Peter_Logan@spartanstores.com" <Peter_Logan@spartanstores.com> To: ids@iiug.org Date: 08/18/2011 07:18 AM Subject: ids 11.70.fc3 read ahead [24649] Sent by: ids-bounces@iiug.org Aix 6.1 Prior to moving to the above version we had read ahead set to 1024 and 512 .... When we came up on 11.70.fc3, we turned on the AUTO_READAHEAD. 4 days later started crashing, so after working with Tech Support we switched back to using RA_PAGES and turning off AUTO_READAHEAD. Now our performance seems to be severely impacted. Has anyone else had any negative impact with this? Thanks Peter Logan Senior Database Administrator Phone: 616/878-8309 ******************************************************************************* Forum Note: Use "Reply" to post a response in the discussion forum.
Because the only parameter that we changed was the AUTO_READHEAD and RA_PAGES... when auto_readhead was set to 0 and RA_PAGES 1024, the performance is horrible. Queries that run in minutes never finish ... scripts that consistently have run 10 minutes jumped to 35 minutes .. etc. As soon as AUTO_READAHEAD is set back to 1, every thing works ok again ... Tec Support isn't convince that it's RA, but what else could it be.... Peter Logan Senior Database Administrator Phone: 616/878-8309 From: "Madison Pruet" <mpruet@us.ibm.com> To: ids@iiug.org Date: 08/18/2011 10:05 PM Subject: Re: ids 11.70.fc3 read ahead [24652] Sent by: ids-bounces@iiug.org Why did tech support think that AUTO_READAHEAD was the cause? From: "Peter_Logan@spartanstores.com" <Peter_Logan@spartanstores.com> To: ids@iiug.org Date: 08/18/2011 07:18 AM Subject: ids 11.70.fc3 read ahead [24649] Sent by: ids-bounces@iiug.org Aix 6.1 Prior to moving to the above version we had read ahead set to 1024 and 512 ..... When we came up on 11.70.fc3, we turned on the AUTO_READAHEAD. 4 days later started crashing, so after working with Tech Support we switched back to using RA_PAGES and turning off AUTO_READAHEAD. Now our performance seems to be severely impacted. Has anyone else had any negative impact with this? Thanks Peter Logan Senior Database Administrator Phone: 616/878-8309 ******************************************************************************* Forum Note: Use "Reply" to post a response in the discussion forum. ******************************************************************************* Forum Note: Use "Reply" to post a response in the discussion forum.
it could be a defect as it seems to be that read head is behaving in either passive mode or not behaving period. # If the AUTO_READAHEAD configuration parameter is is set to 0 and there is no RA_PAGES information, the server performs passive read-ahead on 128 data pages when completing a query. So its seems as if RA_PAGES 1024 and AUTO_READAHEAD 0 is handled in-correctly by the engine. In your case it seems RA_PAGES is being ignored entirely. I would continue pursuing this with tech support.
I am ... because as it is now with the AUTO_READAHEAD turned back on we can crash the system with a particular query ... So, there definitely is something messed up. Thanks ... Peter Logan Senior Database Administrator Phone: 616/878-8309 From: "MARK JALKIEWICZ" <mark.jalkiewicz@verizon.net> To: ids@iiug.org Date: 08/19/2011 09:12 AM Subject: Re: ids 11.70.fc3 read ahead [24654] Sent by: ids-bounces@iiug.org it could be a defect as it seems to be that read head is behaving in either passive mode or not behaving period. # If the AUTO_READAHEAD configuration parameter is is set to 0 and there is no RA_PAGES information, the server performs passive read-ahead on 128 data pages when completing a query. So its seems as if RA_PAGES 1024 and AUTO_READAHEAD 0 is handled in-correctly by the engine. In your case it seems RA_PAGES is being ignored entirely. I would continue pursuing this with tech support. ******************************************************************************* Forum Note: Use "Reply" to post a response in the discussion forum.