Re: Journal file

Hi,

Mckoi uses the journal files to store changes made to the data files 
between commits.  If you increase the commit frequency then the journal 
files will flush more often.  Likely the bottleneck you are experiencing 
here is that the journal files are reaching maximum capacity and so the 
system has to force a flush which temporarily stops IO until complete.

If the cache/journal is reaching maximum capacity, you may find that 
increasing the 'buffered_io_max_pages' in your configuration will help 
matters.  It defaults to 256, which allocates about 2MB to the cache. 
If you increase this to 512 or 1024 you may not see so many journal flushes.

The best plan is always to keep 'commit' to a minimum when updating the 
database to maximize throughput.

Toby.


Philippe Bosse wrote:
> Hi Toby,
> 
> Have a couple of questions, but first here's our system:
> Db runs as a standalone aps
> We have 80 connections to the db at all time
> 10 worker threads
> Auto-commit is off but we commit after every transaction(need to change 
> that)
> We have 16 tables with 2 tables containing roughly 2000 rows each
> 
> Here's how our apps work(4 different jvm):
> At start up update the 2000 rows to change the status
> Then start updating various field, or insert new rows, as changes are 
> coming from our network.
> 
> Overall McKoi work very well, except when we receive lots of events from 
> the network that we have to update/insert.  The journaling file gets 
> huge, around 24Megs(increasing steadily), the cpu reaches 50% (2 cpu 
> machine) and the memory is acceptable around 70megs  After 25 min. it 
> settles down to.5%-1% and journal files will go back to almost 0, but 
> during that time period it's seems that everything is hung.  Doing a 
> simple select won't work until the db starts to settle down.
> 
> My questions are, is there a limit to the journal file? Shouldn't McKoi 
> reponds to a simple select? Does having auto-commit off and commiting 
> nonetheless at every transaction make the journal file bigger?  I am 
> also concerned that the DB reaches 50% on the cpu.  What is the maximum 
> number of connections that is acceptable per worker threads?
> 
> Once the db goes down to listening events it works very well, very small 
> db file, around 9 megs total.
> 
> Thanks!
> -P.
> 



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