Re: Online Physical Log Question

jgoers@interramp.com wrote: : I am working on a system experiencing slow database insert/select : throughput (HP9000 Online 5). I believe part of the problem is a very : small physical log file size - 1MB. (The logical logs are also small : at 1/2MB). I have 2 questions: : 1. What impact does the physical log file size have on performance? The physical log stores before-images of modified pages in th buffer pool. When the physical log becomes 75% full a checkpoint will occur. During a checkpoint all buffer pool modification is suspended. If the P.L. is too small, checkpoints will occur frequently, thus interrupting processes that are modifying buffer pool pages. You can check the frequency of checkpoints by examining the OnLine log. You should also measure how efficiently you are using your page cleaners between checkpoints with tbstat -F. You should see 0 foreground writes and at least some LRU writes. By lengthening the checkpoint interval, LRU writes become more important to keep the buffer pool clean. : 2. What is the process for changing its size? Does Online have to be : re-initialized or can it just be changed and brought back up? You need only quiesce the system, not reinitialize rootdbs. The size and location of the physical log can be changed using tbmonitor. : regards, : jgoers@interramp.com -- ___ ___ Principal Consultant / ) __ . __/ /_ ) _ _ __ Informix Software Inc. (303) 850-0210 _/__/ (_(_ (/ / (_(_ _/__) (-' ~/ '(_- 5299 DTC Blvd #740 Englewood CO 80111 dberg@informix.com Opinions expressed herein are my own. Eventually all things merge into one...and a river runs through it. -N.Maclean