LRUs Writes / Chunk Writes
John Smith asked whether LRU writes should be lower than chunk writes in onstat -F. Art Kagel said it is debated; LRU writes ease checkpoints and about 70-75 percent LRU writes tuned OLTP faster, while bulk loads suit a more balanced mix. ZhiWei Cui said it depends on disk IOPS capability. Art agreed tuning depends on hardware and workload.
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Hello Reading Onstat -F, there are LRUs writes more than Chunk writes should LRUs Writes be 0 or at least less than chunk writes ? Thanks :) ------------------------------ John Smith ------------------------------ #Informix
John: That's an open debate. Chunk writes are more efficient overall for the storage system LRU writes minimize the overhead of checkpoints and reduce the number of chunk writes which can overwhelm the system Mostly I know that when I tune a system to be about 70-75% LRU writes it runs faster. Especially for OLTP workloads, but bulk loads type workload also to some extent. Art ------------------------------ Art S. Kagel, President and Principal Consultant ASK Database Management Corp. www.askdbmgt.com ------------------------------
I think it has more to do with the ability of disk IOPs. If the IOPs capability of the disk is very good, you need to adjust the LRU a little larger and make use of the write efficiency of chunk. If the IOPs performance is poor, it is recommended to adjust the LRU lower to reduce the transaction blocking caused by CKPT. ------------------------------ ZhiWei Cui GBASE ShiJiaZhuang ------------------------------
Well taken points! I agree. But my point holds that for OLTP workloads, heavier LRU writes versus chunk writes is better, while for bulk load workloads, a more balanced or even chunk write heavy configuration is better. You are correct, one has to tune for the hardware, but also for the workload. Everything we do as DBAs involves tradeoffs. ------------------------------ Art S. Kagel, President and Principal Consultant ASK Database Management Corp. www.askdbmgt.com ------------------------------