Hello

as recommandation, Cleaner parameter should be equal to number of chunks or number of disks ?

Thanks

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John Smith
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#Informix

John:

Whenever buffer flushing is initiated, whether for chunk writes or LRU writes, either a chunk or an LRU queue's dirty buffers are assigned to a cleaner. So, for maximum write throughput, you need one cleaner for each chunk at checkpoint time or one for each LRU queue at LRU flush time.

Now, I note that the maximum number of LRU queues per buffer cache is 512 and you could have multiple caches and that the maximum number of CLEANERS is 128. I would also note that you can discount any chunks that only contain static data when considering the number of chunks.

Obviously I disagree with the recommendations in the IBM manuals, so your decision: one per chunk, one per LRU, one per disk, or one for every 2 disks.

Art

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Art S. Kagel, President and Principal Consultant
ASK Database Management Corp.
www.askdbmgt.com
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Original Message:
Sent: 11/17/2021 6:30:00 AM
From: Art Kagel
Subject: RE: question about Cleaner Parameter

John:

Whenever buffer flushing is initiated, whether for chunk writes or LRU writes, either a chunk or an LRU queue's dirty buffers are assigned to a cleaner. So, for maximum write throughput, you need one cleaner for each chunk at checkpoint time or one for each LRU queue at LRU flush time.

Now, I note that the maximum number of LRU queues per buffer cache is 512 and you could have multiple caches and that the maximum number of CLEANERS is 128. I would also note that you can discount any chunks that only contain static data when considering the number of chunks.

Obviously I disagree with the recommendations in the IBM manuals, so your decision: one per chunk, one per LRU, one per disk, or one for every 2 disks.

Art

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Art S. Kagel, President and Principal Consultant
ASK Database Management Corp.
www.askdbmgt.com
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Original Message:
Sent: 11/18/2021 9:12:00 AM
From: TOM GIRSCH
Subject: RE: question about Cleaner Parameter

I've rarely seen a penalty for having too many cleaners configured. The exception would be when you have many chunks on few slower spinning disks (as opposed to SSD), in which case, I wouldn't go more than 2 per disk. Problem is, with modern storage and SANs, you may not actually know how many disks there are behind the scenes. In that case, I'd generally follow Art's recommendation of one per frequently-written chunk.