FreeTDS Development Group

["Frediano Ziglio" <freddy77 AT gmail.com>]

>
>
>
> Il giorno mar, 04/11/2008 alle 20.48 -0800, Man Min Yan ha scritto:
>> > Hi Frediano,
>> >
>> > You're right, tds_free_dynamic doesn't seem to be right. It's not
>> removing the items from the tds->dyns list properly. Also, my previous 
>> patch
>> is not right as it would throw away any previously prepared statement.
>> Here's my 2nd go at fixing this problem.
>> >
>> > I've also tried to identify where the prepares were happening, and it
>> seems to be a freetds problem. Here's the call stack:
>> >     main()
>> >     perl_run()
>> >     Perl_runops_standard()
>> >     Perl_pp_entersub()
>> >     XS_DBI_dispatch()
>> >     XS_DBD__ODBC__st_execute()
>> >     odbc_st_execute()
>> >     SQLExecute()    from libodbc.so.1
>> >     SQLExecute() at odbc.c:3343
>> >     _SQLExecute() at odbc.c:3142
>> >     tds_submit_prepare() at query.c:1007
>> >
>> > The code in _SQLExecute is actually un-preparing the statement,
>> re-preparing it, then executing it every time it is called.
>> >
>> > Rgds,
>> > Man Min
>> >
>>
>> Mmmm... currently there are 3 issues:
>> - generated ids can create duplication leading to dynamic reuse, perhaps
>> we should throw error on same id and generate betters ids. TODO: test in
>> libTDS to check no duplication on generated ids
>
>
> Perhaps the best way is to allow NULL id calling tds_alloc_dynamic and
> generate id in tds_alloc_dynamic. Also I don't understand why
> tds_alloc_dynamic should return same dynamic, perhaps is better to return
> NULL... id duplicated should not be allowed, even by CTLib.(ct_dynamic state
> that id are univoque)
>
>
>>
>> - on reused dynamic I had cur_dyn set but no dynamic on list... that is
>> a huge memory problem! TODO: test in odbc to remove the problem
>
>
> Mmmm... this is due to tds_alloc_dynamic returning same dynamic, two
> statements have stmt->dyn set on same dynamic so on second
> tds_submit_unprepare you have dynamic not in list, you set tds->cur_dyn and
> you get the error, avoiding duplicate return should fix the problem. Perhaps
> adding reference counting to TDSDYNAMIC would help.
>

Both points done. Now tds_alloc_dynamic accept NULL as id meaning generated
id and never return a previous dynamic.
Fix backported to 0.82 (see freetds.sf.net)


>
>
>>
>> - odbc prepare too much, in this case due to rebinding. TODO: cache
>> argument and query in libTDS to avoid this case.
>>
>
>
> This is a TODO, we should add a test on freeclose test which already could
> round_trips and inserts (but with another SQLFreeStmt option).
>

I'll put this in my TODO list...

freddy77