Re: LINUX Kernel (kswapd) and INFORMIX

Run onstat -g seg to see if the engine has grabbed additional VIRTUAL segments for sorting purposes. If you are running with a high PDQPRIORITY value PDQ will require additional memory depending on the DS_TOTAL_MEMORY and SHMTOTAL. If SHMTOTAL is zero and DS_TOTAL_MEMORY is high then sorting or complex queries can cause the engine to add lots of memory to optimize the query/sort processing which can cause the OS to swap. Art S. Kagel ----- Original Message ----- From: Mike Van Tress <stress@xprt.net> At: 3/ 3 20:35 > Operating System: Red Hat 7.1 Kernel 2.4.9 > Hardware: Compaq DL-580 4-CPU 16GB ram > Informix: IDS ver 7.3 UD1 > Database size: 4GB > > Problem: We are experiencing huge performance degradations > when we run rather large transactions, queries, or even update statistics > high . When investigating the system load (via the top command), the > kswapd process is taking most of the resources. The interesting point is > that the database is only 4GB, and my shared memory segments are nowhere > near 4GB. Why would the system be swapping memory? > > Question: Has anyone here experienced this problem on a LINUX > based Informix system? If so, would you mind sharing your fix if you were > able to find one? Thanks a bunch! > > -Mike-

ART KAGEL, .... wrote: > Run onstat -g seg to see if the engine has grabbed additional VIRTUAL segments > for sorting purposes. If you are running with a high PDQPRIORITY value PDQ will > require additional memory depending on the DS_TOTAL_MEMORY and SHMTOTAL. If > SHMTOTAL is zero and DS_TOTAL_MEMORY is high then sorting or complex queries can > cause the engine to add lots of memory to optimize the query/sort processing > which can cause the OS to swap. It doesn't matter, Art. It's a well known issues of the earlier 2.4 Linux kernels ( a lot of problems with VM subsystem ) plus I guess they are using cooked files instead of raw devices, so this causes unlimited growing of the fs cache and thus memory shortage. ( One of the issues ). The latest 2.4 kernels has no this class of problems. ( Except may be same edge cases ). > > Art S. Kagel > > ----- Original Message ----- > From: Mike Van Tress <stress@xprt.net> > At: 3/ 3 20:35 > > >>Operating System: Red Hat 7.1 Kernel 2.4.9 >>Hardware: Compaq DL-580 4-CPU 16GB ram >>Informix: IDS ver 7.3 UD1 >>Database size: 4GB >> >>Problem: We are experiencing huge performance degradations >>when we run rather large transactions, queries, or even update statistics >>high . When investigating the system load (via the top command), the >> kswapd process is taking most of the resources. The interesting point is >>that the database is only 4GB, and my shared memory segments are nowhere >>near 4GB. Why would the system be swapping memory? >> >>Question: Has anyone here experienced this problem on a LINUX >>based Informix system? If so, would you mind sharing your fix if you were >>able to find one? Thanks a bunch! >> >>-Mike- > > > > >