Re: Mirroring

Jay Aymond wrote: > > I am adding mirroring to my Informix Online 5.x installation. Right now, I have > Cleaners set to 2 for my two primary disk drives. Once I have enabled > mirroring, should I change the number of Cleaners from 2 to 4 since I will have > more disk drives, even though two of them are mirrored drives? If you want to use the formula of one cleaner per drive, yes. I assume that tbstat -F shows most of your activity as 'Chunk Writes'? If so, and this is primarily a query database, then this scheme may work best. BUT, if your instance is a high update transaction server, it tends to get better database performance by reducing MAX_DIRTY and MIN_DIRTY and increase the number of cleaners to match the number of LRU queues, which should be 16, 32, or 64 depending on how large you buffer pool is. This will result in 2/3 or more of your buffer flush activity being LRU Writes and Idle Writes. The trade off is that the Informix engine will have a greater impact on the system's I/O subsystem and not be as good at 'Playing Nicely' with non-database applications. I know what the manuals say (one cleaner per disk and fewer LRUs is better). The manuals are WRONG. The Informix benchmark people long ago proved that and I have verified it myself. If your goal is to best share the machine with other apps and servers and minimize impact on the OS and hardware, follow the manuals. If you want maximum transaction throughput, for BUFFERS=100000 go with 32 LRUs, 32 cleaners, MAX_DIRTY < 10, MIN_DIRTY < 5. Adjust as appropriate. In this scheme ignore the fact that you have mirrors, there will be plenty of free cleaners to flush to the mirrors during Idle Write wake ups and LRU wake ups and if your activity level is so high that there are still significant numbers of dirty pages at checkpoint time you know that there will be more cleaners than disk so... With this scheme checkpoints are MUCH shorter and applications rarely have to wait for page flushes during checkpoints. I run my busiest servers with LRU_MAX_DIRTY=3 and LRU_MIN_DIRTY=0 90% LRU Writes, these puppies fly! Art S. Kagel