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тАО11-04-2003 03:47 PM
тАО11-04-2003 03:47 PM
Asynchronous I/O for uncooked file system - Informix
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тАО11-04-2003 08:28 PM
тАО11-04-2003 08:28 PM
Re: Asynchronous I/O for uncooked file system - Informix
Nearly all informix reads are asynchronous.
The only synchronous writes are checkpoints (unavoidable) and foreground writes (undesirable). Apart from that, the database either uses its own AIO virtual processors to service requests or KAIO if you configure it.
KAIO puts a reduced load on the server due to fewer processes, but increases the system load in kernel routines.
The issue with AIO VPs is that they all get scheduled with every other process on the server (more waits), whereas KAIO goes straight to the kernel from the CPU VP that requests it.
I have found that KAIO improves performance, but doesn't work well on more than one instance per machine. Keep the less important instances as non-KAIO. Also you should export IFMX_HPKAIO_NUM_REQ=3000 or so for a busy instance.
If you want cooked files, it is important that you bypass the HP-UX buffer cache, otherwise the logical and physical log records might not get flushed to disk if the server TOCs or PANICs, so you would end up losing integrity.
On old operating systems (<11.xx) and older versions of IDS (<7.3) the KAIO wasn't so good but these days its fine.
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тАО11-05-2003 11:41 AM
тАО11-05-2003 11:41 AM
Re: Asynchronous I/O for uncooked file system - Informix
I do mean KAIO and raw filesystems for informix
Does anyone else have any feedback ??
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тАО11-05-2003 01:29 PM
тАО11-05-2003 01:29 PM
Re: Asynchronous I/O for uncooked file system - Informix
The issue I think is relevant includes the type of disk sub-system you are using. Is it a set of JBOD's, an xp512, something with lot's of memory cache, multiple pathing, etc. Raw disk io does eliminate the OS buffering and overhead. But if you are using 10k disks on a very intelligent san or disk sub-system or multiple dbspaces, fragmentation and pdq, the impact maybe neglible. Your milage may vary!!!!!
Also, if you use cooked files, there are those who say you can use a OS back up utility (Veritas, tar, fbackup, etc) with success; giving you a secondary means of back up and disaster recovery. I have no exp with this but am just passing along 2nd hand info.
Hope this helps,
Doug
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тАО11-05-2003 02:40 PM
тАО11-05-2003 02:40 PM
Re: Asynchronous I/O for uncooked file system - Informix
We are using an EMC symm
So that is one for one against
Is there any other imput
both of your imputs have been helpful
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тАО11-10-2003 10:12 AM
тАО11-10-2003 10:12 AM