Scope for small (5%) speed improvement in Tablix

From: John Winters <johnREMOVE@THISsinodun.org.uk>
Date: Thu Jul 22 2004 - 09:51:39 CEST

Hi all,

I've been studying the code of Tablix with a view to improving my
understanding of how it works.

One oddity I noticed is that the "tuplemap" data structure is
dynamically allocated, despite being of fixed size. Each access then
requires a double indirection instead of a simple array index.

By changing tuplemap from:

    tuple **tuplemap

to:

    tuple tuplemap [TUPLEMAX];

removing the dynamic memory code and amending all accesses from:

    tuplemap [c]->cid;

to:

    tuplemap [c].cid;

I found an overall 5% increase in my GPM figure on a single CPU.

Drawbacks:

1) Memory use. Instead of using between 4k and 24k of RAM the new
version uses a fixed 20k. Both I feel are small enough not to worry
about.

2) All modules which reference tuplemap need to be upgraded. This took
me less than 5 minutes. "vi `grep -l tuplemap *.c`

I put it forward just in case it's acceptable.

Cheers,
John
Received on Sat Jul 24 23:36:07 2004

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