[fpc-devel] What do you think about TSQLScript using 'TextReader'?

[Michael Van Canneyt]

On Sun, 14 Jun 2015, silvioprog wrote:

> Hello,
> 
> A few weeks ago, I took a look at the TSQLScript (that IMHO is a very nice class!) source, and I noticed that it seems slow for processing big files.
> 
> I did some tests with this class. My SQL file: 90 MB, with CREATE TABLE, CREATE PROCEDURE, CREATE TRIGGER, ALTER TABLE, several INSERT INTO and more. Using the current TSQLScript
> implementation, the execution of this file is very slow, and the CPU/memory usage is extremely large(*), but after make some changes in the original TSQLScript source code, adapting it to
> use this[1] new class (recently applied in FCL), I got a significant difference, ie, the CPU/memory usage now is amazing less, increasing the performance +-80%. =) The answer to the
> significant gain is simple: using a textreader, the TSQLScript class read the SQL (from string, stream or file) by demanding (line by line, and using a low level byte reading too), instead
> of loading an entire file to a buffer in a stringlist.

I think you hit the stringlist performance limit with 90 mb =)

> 
> So, after this explanation, what do you think about TSQLScript using textreader? I can send a patch showing this idea as a real implementation, of course, keeping the 'Script' as a
> stringlist, just adding a new property, called 'Source' and declared as 'TTextReader'.

I think this is a good idea.

> 
> An observation: I suspect it has a small bug at this line[2]: the 'Directive' variable could break the loop skipping for the next line after its assignment. OK, if it is a bug, it is very
> easy to fix.

Please report it in the bugtracker.

> 
> (*) In a specific case on a Linux server, the kernel killed my executable while importing my SQL file, see more details here[3].
> [1] http://bugs.freepascal.org/view.php?id=28075
> [2] https://github.com/graemeg/freepascal/blob/master/packages/fcl-db/src/base/sqlscript.pp#L387
> [3] http://unix.stackexchange.com/questions/136291/will-linux-start-killing-my-processes-without-asking-me-if-memory-gets-short

If you want, you can create a patch and put it in the bugtracker. 
Anything to improve performance is welcome.

Michael.