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In article <3d4q2d$ipu@net.auckland.ac.nz>, mmohr@ait.ac.nz (Mike Mohr)
says:
>
>I know how to increase the number of write threads that Ingres uses.  
>What I need to know is how to increase the number of READ threads.  Our 
>system is heavily read bound and locked to a single thread.
>-- 

Ingres' caching algorithm is such that it will first choose a 'read' page
to replace in the cache before it chooses a 'write' or 'dirty' page. 
(Naturally, since a write page has to be written first.)

On applications which are primarily read applications, I have seen the
cache be taken over by modified pages.  There are several things you can
do to preserve a large portion of the cache for your 'read' pages.  I
assume you are using FAST_COMMIT.

1)  Increase your consistency point intervals
2)  Set your write_behind threads to wake up early and often.  The default
    is at 50% dirty, and they quit writing at 40% dirty.  I have been known to
    configure a 10,000 page cache with wb_start at 200 and wb_end at 50.  Boy
    do those suckers stay active!
3)  Set the mlimit very low, (although I prefer #2 to this option).

Monitor the write_behind thread usage through the DM420 trace point.

Hope this helps, but remember to measure, change 1 thing, measure, and
learn.  Of all the servers/machines/applications/databases I have looked
at, I have found each to be unique, and to learn something new each time.

Mark Kale
York & Associates, Inc.




Mike Mohr (mmohr@ait.ac.nz) wrote:
: I know how to increase the number of write threads that Ingres uses.  
: What I need to know is how to increase the number of READ threads.  Our 
: system is heavily read bound and locked to a single thread.

Have you tried increasing your cache?  You can modify the following parameters:

-dmf.cache_size n (Don't forget to up your locks proportionally)
-dmf.size_read_ahead
-dmf.count_read_ahead

This will allow more info to be held in cache and improve reduce I/O
bottlenecks.

Hope this helps...

Jon
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