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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Choosing data file size for a multi TB database?
Hi Matthew,
I agree that CKPT may become the bottleneck soner then
I thought.
It looks obvious that CKPT breaking point is when DBWR
is faster doing I/O in parallel while CKPT needs to do
things in serial and suddenly becomes the bottleneck
in doing the database checkpoint.
I agree that the CKPT can be slow because it needs to write all things to the control file, read and write to the datafile header (direct path read and write), ....
But I am curious out of these 15 minutes what is taking the majority of time? Which waits?
If you have 4000 files you will probably need at least 4000 + (the number of control files) * 4000 writes and at least 4000 reads + not sure how many control file sequential reads.
We all know that just doing 20000 I/O operations are
taking some time :)
Is this the case here?
Regards,
Zoran
> In Oracle a large number of datafiles do affect you
> administratively and in recovery.
>
> In a 22TB database that has +4500 files. A simple
> query such as
> select tablespace_name,sum(bytes)/1024/1024 from
> dba_segments group by tablespace_name;
>
> takes 5 minutes and that is not indicative of a
> large number of objects, it is indicative of the
> freespace bitmap walk across the datafiles (locally
> managed tablespaces). Under some circumstances or
> patch versions it can take much longer.
>
> Also in examination of this database even under low
> load the time to check point is 15 minutes and many
> times overlays the next log switch. Someday Oracle
> will parallelize the CKPT process, similar to how it
> is done on recovery.
>
-- http://www.freelists.org/webpage/oracle-lReceived on Tue Sep 06 2005 - 16:27:29 CDT
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