Re: Buffer Requests Trace

Sorry for taking so long to answer. I am sending attached the patch with
the changes I did to pgsql code. I followed the steps for compiling and
installing pgsql from:
http://www.postgresql.org/docs/current/static/install-short.html

In summary, the page_id of the page being released in ReleaseBuffer() and
ReleaseAndReadBuffer() is written to the file: /usr/loca/pgsql/data/trace.
This file is created manually.

I have also created a PrivateDirtyFlag for each backend, in analogy to the
PrivateRefCount. I use this to keep track if the current backend performed
an update operation in a page in the buffer pool or simply a read operation
(it is not relevant now). The trace file consists of one line for each
ReleaseBuffer() or ReleaseAndReadBuffer() call. The line has the format:

operation,tblSpace,dbNode,relNode,blockNumber

Once the trace file is complete after the execution of the tpcc benchmark,
I use the following bash script to get only unique pages:

cut -d',' -f2-5 trace | sort -n -t',' -k1 -k2 -k3 -k4 | uniq

Today I realized that I was making a mistake in executing the
oltpbenchmark application. From the 64 warehouses created for tpcc, only 1
was being accessed (the 14k distinct pages that I mentioned). I increased
the "terminal" option of the tpcc benchmark from 1 to 64, resulting in one
terminal for each warehouse.

This provided me with a higher number of distinct pages being
accessed. Unfortunately, from the 800k pages in the database (64
warehouses), executing tpcc for 10min resulted in 400k distinct pages being
accessed. This number is much better than the previous results, but I think
it is still not realistic.

I would like to thank you guys for all the attention given to my problem :)

On Wed, Oct 15, 2014 at 9:49 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:

> On 14 October 2014 17:08, Lucas Lersch <lucaslersch(at)gmail(dot)com> wrote:
>
> > Unfortunately, in the generated trace with over 2 million buffer
> requests,
> > only ~14k different pages are being accessed, out of the 800k of the
> whole
> > database. Am I missing something here?
>
> We can't tell what you're doing just by knowing the number of unique
> items in your list.
>
> --
> Simon Riggs http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services
>

--
Lucas Lersch