{Spam?} Re: [Ocfs2-users] Performance Problems while reading

[Sunil Mushran]

Egon Burgener wrote:
>> And you are convinced that drdb's primary-primary is not the
>> cause for the slowdown. ??
>>     
> Yes, writing a file is fast. Reading a file has no influence on drbd.
>
> We noticed, that reading a big file on one node while the other node
> opened that file in RW mode but without writing anything is still fast.
>   
That's not surprising as both nodes with be holding PR locks on the lockres.

> If the writing node writes slowly to the file (e.g. a logline per
> second) reading from the other node is also fast.
Here the write nodes lock is ping ponging between EX and PR whereas read 
nodes
is between NL and PR.

>  As soon as the writing
> speed increases (e.g. a logline per 1/3 second) reading blocks. While
> tcpdumping all these scenarios we noticed, that the blocking scenario
> produces much more connections (ocfs2 protocol).
>   
Reading blocks? or is it very slow? How are you doing the reads? tail -f?
Can you share the tcpdumps with me?

> Finally we tried to buffer the write operations and flushing it each
> second. The result was, that writing many loglines per second did not
> block the reading process on the other node
How are you buffering? As in, are you saying that you were using o_sync
and no longer using that (or reducing the number of fsyncs). Or, is the 
buffering
in the app layer?

I mean, if you are issuing writes (buffered or not), ocfs2 will still 
take the appropriate
lock level.