When is read-ahead used?

Posted in 2011

Topics: Performance & Tuning, Installation, Setup & Upgrades

red_valsen — Mon, 28 Nov 2011 05:33:54 -0800 (PST) — source: Usenet: comp.databases.informix

We're testing IDS 11.70.FC3 on RHEL5.7/2.6.18 for a data warehouse application, and had to turn read-ahead off due to the instance- crashing bug related to RA. But now the project is reporting that their ETL routine has doubled in duration. However, release FC4 fixes the RA bug. Does Informix use read-ahead for inserts? If so, an upgrade may fix the reported performance problem, too.

↪ replying to red_valsen

LIGHT SCANS — Mon, 5 Dec 2011 14:54:35 -0800 (PST) — source: Usenet: comp.databases.informix

RA (Read Ahead) is primarily for reading ahead if you are doing scans. You probably have some other issue(s) slowing down your inserts. Follow the bytes from source to destination: Are the reading disks slow? The network slow? The writing disks slow? Etc. Anything different from the way you did it on the old system? Try running "vmstat" or "sar" during the slow inserts to see if anything is bad (IO waits, swapping, etc). Lastly, look at ONCONFIG. -LS

Glossary

IDS (Informix Dynamic Server)