December 15, 2012
On 2012-12-14 19:27, Rob T wrote:

> I wonder what can be done to allow a programmer to go fully manual,
> while not loosing any of the nice features of D?

Someone has create a GC free version of druntime and Phobos. Unfortunately I can't find the post in the newsgroup right now.

-- 
/Jacob Carlborg
December 15, 2012
On Saturday, 15 December 2012 at 11:35:18 UTC, Jacob Carlborg wrote:
> On 2012-12-14 19:27, Rob T wrote:
>
>> I wonder what can be done to allow a programmer to go fully manual,
>> while not loosing any of the nice features of D?
>
> Someone has create a GC free version of druntime and Phobos. Unfortunately I can't find the post in the newsgroup right now.

http://3d.benjamin-thaut.de/?p=20
December 15, 2012
On Saturday, 15 December 2012 at 13:04:41 UTC, Mike Parker wrote:
> On Saturday, 15 December 2012 at 11:35:18 UTC, Jacob Carlborg wrote:
>> On 2012-12-14 19:27, Rob T wrote:
>>
>>> I wonder what can be done to allow a programmer to go fully manual,
>>> while not loosing any of the nice features of D?
>>
>> Someone has create a GC free version of druntime and Phobos. Unfortunately I can't find the post in the newsgroup right now.
>
> http://3d.benjamin-thaut.de/?p=20

Thanks for the link, Windows only and I'm using Linux, but still worth a look.

Note this, comment below, a 3x difference, same as what I experienced:

Update:
I found a piece of code that did manually slow down the simulation in case it got to fast. This code never kicked in with the GC version, because it never reached the margin. The manual memory managed version however did reach the margin and was slowed down. With this piece of code removed the manual memory managed version runs at 5 ms which is 200 FPS and thus nearly 3 times as fast as the GC collected version.
December 16, 2012
On Friday, 14 December 2012 at 19:24:39 UTC, Rob T wrote:
> On Friday, 14 December 2012 at 18:46:52 UTC, Peter Alexander wrote:
>> Allocating memory is simply slow. The same is true in C++ where you will see performance hits if you allocate memory too often. The GC makes things worse, but if you really care about performance then you'll avoid allocating memory so often.
>>
>> Try to pre-allocate as much as possible, and use the stack instead of the heap where possible. Fixed size arrays and structs are your friend.
>
> In my situation, I can think of some ways to mitigate the memory allocation  problem, however it's a bit tricky when SELECT statement results have to be dynamically generated, since the number of rows returned and size and type of the rows are always different depending on the query and the data stored in the database. It's just not at all practical to custom fit for each SELECT to a pre-allocated array or list, it'll just be far too much manual effort.
>

Isn't the memory management completely negligible when compared to the database access here ?
December 16, 2012
On Sunday, 16 December 2012 at 05:37:57 UTC, SomeDude wrote:
>
> Isn't the memory management completely negligible when compared to the database access here ?

Here are the details ...

My test run selects and returns 206,085 records with 14 fields per record.

With all dynamic memory allocations disabled that are used to create the data structure containing the returned rows, a run takes 5 seconds. This does not return any data, but it runs exactly through all the records in the same way but returns to a temporary stack allocated value of appropriate type.

If I disable the GC before the run and re-enable it immediately after, it takes 7 seconds. I presume a full 2 seconds are used to disable and re-enable the GC which seems like a lot of time.

With all dynamic memory allocations enabled that are used to create the data structure containing the returned rows, a run takes 28 seconds. In this case, all 206K records are returned in a dynamically generate list.

If I disable the GC before the run and re-enable it immediately after, it takes 11 seconds. Since a full 2 seconds are used to disable and re-enable the GC, then 9 seconds are used, and since 5 seconds are used without memory allocations, the allocations are using 4 seconds, but I'm doing a lot of allocations.

In my case, the structure is dynamically generated by allocating each individual field for each record returned, so there's 206,085 records x 14 fields = 2,885,190 allocations being performed. I can cut the individual allocations down to 206,000 by allocating the full record in one shot, however this is a stress test designed to work D as hard as possible and compare it with an identically stressed C++ version.

Both the D and C++ versions perform identically with the GC disabled and subtracting the 2 seconds from the D version to remove the time used up by enabling and disabling the GC during and after the run.

I wonder why 2 seconds are used to disable and enable the GC? That seems like a very large amount of time. If I select only 5,000 records, the time to disable and enable the GC drops significantly to negligible levels and it takes the same amount of time per run with GC disabled & enabled, or with GC left enabled all the time.

During all tests, I do not run out of free RAM, and at no point does the memory go to swap.

--rt
December 16, 2012
Rob T:

> I wonder why 2 seconds are used to disable and enable the GC?

If you want one more test, try to put a "exit(0);" at the end of your program (The C exit is in core.stdc.stdlib).

Bye,
bearophile
December 16, 2012
On Sunday, 16 December 2012 at 07:47:48 UTC, Rob T wrote:
> On Sunday, 16 December 2012 at 05:37:57 UTC, SomeDude wrote:
>>
>> Isn't the memory management completely negligible when compared to the database access here ?
>
> Here are the details ...
>
> My test run selects and returns 206,085 records with 14 fields per record.
>
> With all dynamic memory allocations disabled that are used to create the data structure containing the returned rows, a run takes 5 seconds. This does not return any data, but it runs exactly through all the records in the same way but returns to a temporary stack allocated value of appropriate type.
>
> If I disable the GC before the run and re-enable it immediately after, it takes 7 seconds. I presume a full 2 seconds are used to disable and re-enable the GC which seems like a lot of time.
>
> With all dynamic memory allocations enabled that are used to create the data structure containing the returned rows, a run takes 28 seconds. In this case, all 206K records are returned in a dynamically generate list.
>
> If I disable the GC before the run and re-enable it immediately after, it takes 11 seconds. Since a full 2 seconds are used to disable and re-enable the GC, then 9 seconds are used, and since 5 seconds are used without memory allocations, the allocations are using 4 seconds, but I'm doing a lot of allocations.
>
> In my case, the structure is dynamically generated by allocating each individual field for each record returned, so there's 206,085 records x 14 fields = 2,885,190 allocations being performed. I can cut the individual allocations down to 206,000 by allocating the full record in one shot, however this is a stress test designed to work D as hard as possible and compare it with an identically stressed C++ version.
>
> Both the D and C++ versions perform identically with the GC disabled and subtracting the 2 seconds from the D version to remove the time used up by enabling and disabling the GC during and after the run.
>
> I wonder why 2 seconds are used to disable and enable the GC? That seems like a very large amount of time. If I select only 5,000 records, the time to disable and enable the GC drops significantly to negligible levels and it takes the same amount of time per run with GC disabled & enabled, or with GC left enabled all the time.
>
> During all tests, I do not run out of free RAM, and at no point does the memory go to swap.
>
> --rt

Adding and subtracting times like this doesn't give very reliable results. If you want to know how much time is taken by different parts of code, I suggest you use a profiler.
December 16, 2012
On Sunday, 16 December 2012 at 07:47:48 UTC, Rob T wrote:
> On Sunday, 16 December 2012 at 05:37:57 UTC, SomeDude wrote:
>>
>> Isn't the memory management completely negligible when compared to the database access here ?
>
> Here are the details ...
>
> My test run selects and returns 206,085 records with 14 fields per record.
>
> With all dynamic memory allocations disabled that are used to create the data structure containing the returned rows, a run takes 5 seconds. This does not return any data, but it runs exactly through all the records in the same way but returns to a temporary stack allocated value of appropriate type.
>
> If I disable the GC before the run and re-enable it immediately after, it takes 7 seconds. I presume a full 2 seconds are used to disable and re-enable the GC which seems like a lot of time.
>
> With all dynamic memory allocations enabled that are used to create the data structure containing the returned rows, a run takes 28 seconds. In this case, all 206K records are returned in a dynamically generate list.
>
> If I disable the GC before the run and re-enable it immediately after, it takes 11 seconds. Since a full 2 seconds are used to disable and re-enable the GC, then 9 seconds are used, and since 5 seconds are used without memory allocations, the allocations are using 4 seconds, but I'm doing a lot of allocations.
>
> In my case, the structure is dynamically generated by allocating each individual field for each record returned, so there's 206,085 records x 14 fields = 2,885,190 allocations being performed. I can cut the individual allocations down to 206,000 by allocating the full record in one shot, however this is a stress test designed to work D as hard as possible and compare it with an identically stressed C++ version.
>
> Both the D and C++ versions perform identically with the GC disabled and subtracting the 2 seconds from the D version to remove the time used up by enabling and disabling the GC during and after the run.
>
> I wonder why 2 seconds are used to disable and enable the GC? That seems like a very large amount of time. If I select only 5,000 records, the time to disable and enable the GC drops significantly to negligible levels and it takes the same amount of time per run with GC disabled & enabled, or with GC left enabled all the time.
>
> During all tests, I do not run out of free RAM, and at no point does the memory go to swap.
>
> --rt

Use the stopwatch class from std.datetime to get a proper idea of where time is being spent. All this subtracting 2 secs business stinks.

or just fire up a profiler.
December 16, 2012
On 2012-12-15 14:04, Mike Parker wrote:

> http://3d.benjamin-thaut.de/?p=20

That's it, thanks.

-- 
/Jacob Carlborg
December 16, 2012
On Sunday, 16 December 2012 at 11:43:20 UTC, John Colvin wrote:
> Use the stopwatch class from std.datetime to get a proper idea of where time is being spent. All this subtracting 2 secs business stinks.
>
> or just fire up a profiler.

I am using the stopwatch, but had not gotten around to wrapping around things for the extra detail. The subtractions and so forth was roughly calculated on the fly while I was posting and noticing new things I hadn't notice before.

The fact is disabling and enabling the GC added on an extra 2 secs for some reason, so it's of interest knowing why. I'll do proper timing later and post the results here.

--rt
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