RE: "db file sequential read" latency during reads versus update activity

I believe the way SLOB works is that the column updated in not indexed. It was done on purpose for precisely the same reason that you have described below but the goal of the tool is to drive IO and not to spend time on CPU operations.

Thanks
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Mladen Gogala Sent: Saturday, March 10, 2018 10:01 PM
To: oracle-l_at_freelists.org
Subject: Re: "db file sequential read" latency during reads versus update activity

Well, when you have updates, your index block may need to be rebuilt. The "db file sequential read" is an index read. If the block has been updated, not only does the block need to be rebuilt, the index block also needs to be rebuilt. It takes time, even if both are cached in memory. However, the precise answer to your question is not possible. For the precise answer, one would need to profile the running code and see exactly where the time is spent. Only Oracle developers can do that. You may try with strace, to see whether there is another IO that somehow creeps in.

Regards

On 03/08/2018 09:54 AM, Hameed, Amir wrote: I am running SLOB to gauge latency of the storage array. When I configure my test for SELECT only run (no updates), I see average latency of db file sequential read consistently around 3ms. However, as I start to add UPDATE activity to the run, I see average latency of db file sequential read go up in the vicinity of 5ms. Is the cause of this increase in latency due to the commit cleanouts phenomena? The database version is 12.1.0.2. My DB_CACHE size is set to 128M to drive physical IOs and I am running my tests with 64 concurrent users.

Thanks,
Amir

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Mladen Gogala

Database Consultant

Tel: (347) 321-1217

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http://www.freelists.org/webpage/oracle-l Received on Sun Mar 11 2018 - 04:10:01 CET