Re: A sniffer for the buffer

Jonas J wrote:

I took a look in the code again and made some changes. For the readBuffer im doing now:
ReadBuffer(Relation reln, BlockNumber blockNum)      fprintf(fp,"r%u\n",(unsigned int) blockNum); //as defined in header, typedef uint32 BlockNumber;
and from the write pages:
write_buffer(Buffer buffer, bool unpin){      fprintf(fp,"w%d\n",BufferGetBlockNumber(buffer));  //get the blockNumber of this buffer

It's better to keep this discussion going on the list so you can get alternate suggestions besides mine.  The above is better.  You're still missing the relation number, which you're really going to want eventually.  And I think you're still vulnerable to printing the information out before the block is locked properly in the write_buffer case.

So, I had never used DTrace, where can I find some good paper to start studying it ?? Also, do it work with linux, or only solaris ??

You can get it to work on Linux for PostgreSQL use if you use systemtap; there's some people who've posted suggestions about that around.

P.S.: I'm using PostgreSQL 8.1.4 to run with TPCC-UVA benchmarks tests...

Ah.  PostgreSQL 8.1 is significantly slower than the current versions, and you're not going to get as much help with issues related to the source code as if you're using a newer one.  For example, I don't know the 8.1 buffer implementation code nearly as well because I didn't really start tinkering with it until 8.2, so some of the things you're asking about I don't have easy access or recollection of.  Also, the DTrace stuff is only really going to be helpful if you're starting with 8.4.

There may be some work to get TPCC-UVA working with 8.4 though, particularly due to some changes made in 8.3 related to casting data to other types.  There is a TPC-C implementation that's used pretty often by developers here named dbt-2:  http://wiki.postgresql.org/wiki/DBT-2 that will work with a newer version.

--
Greg Smith    2ndQuadrant   Baltimore, MD
PostgreSQL Training, Services and Support
greg@2ndQuadrant.com  www.2ndQuadrant.com


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