FreeTDS Development Group

["Steve Brown (FICC IT)" <Steven.Brown AT macquarie.com>]

Hi, I recently did a small test of performance on freetds library
against Sybase ASE 15.0.3 supplied client-libs on RHEL5.4 x64; and found
freetds to be significantly slower.

After running through callgrind, it seemed that tdsdump_log was the
majority of the difference... spending about 23% of the program time in
this function even though the logging was turned off... it was basically
because this function was called 52M times so the call-overhead was
significant.

Here is a patch to resolve this issue... it uses a macro to check
write_dump variable (renamed to tds_write_dump) before making the
function call.

My timing tests (in seconds, smaller is better) are below; averaged over
5 runs. "real" time can probably be ignored since it includes the
elapsed time spent waiting for my Sybase server to respond.  

 before patch:

Select a varchar column from a big table: 
what, Sybase 15.0.3,  freetds-0.82
time real,  6.3s, 5.8s
time user, 0.90s, 1.69s (quite a lot slower)
time sys, 0.50s, 0.47s

Select varchar,varchar,int columns from a big table: 
what, Sybase 15.0.3,  freetds-0.82
time real,  9.1s, 9.8s
time user, 1.53s, 2.41s (quite a lot slower)
time sys, 0.89s, 0.98s

After patch:

Select a varchar column from a big table: 
what, Sybase 15.0.3,  freetds-0.82
time real,  6.3s, 6.2s
time user, 0.90s, 1.21s (better than unpatched)
time sys, 0.50s, 0.51

Select varchar,varchar,int columns from a big table: 
what, Sybase 15.0.3,  freetds-0.82
time real,  9.1s, 9.2s
time user, 1.53s, 1.59s (better than unpatched and almost same speed as
sybase)
time sys, 0.89s,  1.06s

I believe there are other opportunities for speeding  up tds but I have
not made these as I don't have a good enough understanding of the code,
nor time to test... E.g:

1.
Caching (if possible) the srctype and desttype variables in
buffer_transfer_bound_data... I'm not familiar with the code; but it
would seem sensible to do those calls (desttype =
_db_get_server_type(..),  srctype = tds_get_conversion_type(..) ) just
once for the current result-set and store the results inside the
row->resinfo->columns[i] object.
2.
        use num->array[0] = 0 instead of memset in tds_get_data()
although this may be a security concern (not clearing memory).

Steve



        


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Attachment: patch
Description: patch