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From "Raymond Raymond" <raymond_de...@hotmail.com>
Subject RE: Derby I/O issues during checkpointing
Date Mon, 27 Mar 2006 18:35:34 GMT
Dear Oystein,
  In one of you former mails, you said:

>From: Oystein.Grovlen@Sun.COM (Øystein Grøvlen)

>Some tests runs we have done show very long transaction response times
>during checkpointing.  This has been seen on several platforms.  The
>load is TPC-B like transactions and the write cache is turned off so
>the system is I/O bound.  There seems to be two major issues:
>
>1. Derby does checkpointing by writing all dirty pages by
>    RandomAccessFile.write() and then do file sync when the entire
>    cache has been scanned.  When the page cache is large, the file
>    system buffer will overflow during checkpointing, and occasionally
>    the writes will take very long.  I have observed single write
>    operations that took almost 12 seconds ......
>
>2. What makes thing even worse is that only a single thread can read a
>    page from a file at a time.  (Note that Derby has one file per
>    table). This is because the implementation of RAFContainer.readPage
>    is as follow:
>
>         synchronized (this) {  // 'this' is a FileContainer, i.e. a file 
>object
>             fileData.seek(pageOffset);  // fileData is a RandomAccessFile
>             fileData.readFully(pageData, 0, pageSize);
>	}
>
>    During checkpoint when I/O is slow this creates long queques of
>    readers.  In my run with 20 clients, I observed read requests that
>    took more than 20 seconds ......

I am coding on autimatic checkpoint and incremental checkpoint as
what we discussed before, I finished party of them and trying to
do some test on it. I am really interested in how you observed :
>    I have observed single write
>    operations that took almost 12 seconds ......
and
>    readers.  In my run with 20 clients, I observed read requests that
>    took more than 20 seconds ......

Thanks.


Raymond

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