question about Cleaner Parameter
John Smith asked whether CLEANERS should equal the number of chunks or disks. Art Kagel said maximum write throughput needs one cleaner per chunk at checkpoint or per LRU queue, ignoring static chunks, and disagreed with IBM manuals. Tom Girsch rarely saw a penalty for too many, but no more than two per spinning disk. Paul Watson usually sets 128 on larger systems.
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Hello as recommandation, Cleaner parameter should be equal to number of chunks or number of disks ? Thanks ------------------------------ John Smith ------------------------------ #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 ------------------------------ Art S. Kagel, President and Principal Consultant ASK Database Management Corp. www.askdbmgt.com ------------------------------
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.
Like Tom, I have rarely seen any issues with too many CLEANERS. Unless it is a small system I tend to set at 128 and leave it alone Cheers Paul