Memory leak assigning query parameters
lazarus / 16-Databases

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luca · 2014-02-26 11:10

Hi.
I activated check for memory leaks (-gh) from project options.
I ran the program and when I closed it I received a lot of mem-leaks.
By checking memory address I discovered the problem in assigning
string value to query parameter:

If I use
Code: [Select] query1.paramByName('ID').Value = 'SomeID' I have memory
leak.

If I use
Code: [Select] query1.paramByName('ID').AsString= 'SomeID' No memory
leaks appear.

I'm using Lazarus v1.1 FPC2.7.1 32 bit for Windows

Regards.
Luca

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exdatis · 2014-02-26 11:37

Which database?

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exdatis · 2014-02-26 11:40

Also, if you want, can we see sql statement?

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luca · 2014-02-26 11:42

I'm using TSQLQuery with ODBC connection to MSSQL.

Regards.
Luca

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exdatis · 2014-02-26 13:12

I have no experience with M$Sql, but for many years I use PostgreSQL
and Firebird without problem and with very complex queries and many
parameters. As usual I have a few hundred tables and millions of
records in my db.

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BigChimp · 2014-02-26 13:27

Perhaps a good idea to write a minimal FPC program that demonstrates
the problem, including the DDL needed for creating the db:
http://wiki.lazarus.freepascal.org/Database_bug_reporting#FreePascal
and attach it.

This can be used for others to verify the problem (as an attachment to
a forum post or as an attachment a bug report).
If you raise a bug report, please include th program as well so the
problem can be verified and if it is fixed, the fix can be verified as
well.

IIRC, there were some problems with variants in FPC trunk, but I don't
know whether these still influence parameter binding

See related bug:
http://bugs.freepascal.org/view.php?id=24728

BTW: IIRC, using .Value involves a conversion to variant and from
variant to the actual db datatype. This is a relatively costly
operation and you're much better off directly using the .As...
properties as shown in your second line of code.

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luca · 2014-02-26 14:23

Many thanks BigChimp

I think you're right!
Looking into assembler debug, memory leak is into
SYSTEM_$$_assign$SHORTSTRING$$VARIANT function.

In any case, as you suggested, I'll change all .value with .asString.

Regards.
Luca