don't use rand() for choosing a random song for partymode

[jmarshallnz]

Ideally for Frodo. rand() typically returns a number between 0..32767, so for larger databases doesn't hit every possible row.

@koying: please test mysql. I have a feeling it will be quite slow, but not sure. Easy to test - just start partymode then skip a song.

[Fneufneu]

hum RANDOM() does not exist in MySQL
and i always heard ORDER BY RAND() have some perfs issues.

[jmarshallnz]

Our db layer maps it to rand() for mysql.

[bobo1on1]

If it gets mapped to rand(), how does it improve anything?

[Montellese]

@bobo1on1: That mapping only applies to the use of RANDOM() / RAND() in SQL not in C++.

[jmarshallnz]

@koying ping :)

[koying]

Oups, sorry, slipped through...

Unfortunately, mysql uses "rand()", not "random()": http://dev.mysql.com/doc/refman/5.0/en/mathematical-functions.html#function_rand

[jmarshallnz]

Read up :) - we already take care of that in the database layer. The question is whether this makes things unacceptably slow. Easiest test is partymode with a decent number of songs. The length to queue the next song (i.e. after the first song is over) in the list is of interest.

[koying]

Ok, so:

• Initial party mode is ok (default number of songs)
• Doing first "next" brings an error message and I get this in the log:

11:17:55 T:8092   DEBUG: CMusicDatabase::GetRandomSong query = select * from songview  WHERE songview.idSong not in (6788,9063,9224,6602,9159,7857,7281,8978,7909,9602) ORDER BY RANDOM() LIMIT 1
11:17:55 T:8092   ERROR: SQL: Undefined MySQL error: Code (1305)
                                            Query: select * from songview  WHERE songview.idSong not in (6788,9063,9224,6602,9159,7857,7281,8978,7909,9602) ORDER BY RANDOM() LIMIT 1
11:17:55 T:8092   ERROR: CMusicDatabase::GetRandomSong(songview.idSong not in (6788,9063,9224,6602,9159,7857,7281,8978,7909,9602)) failed

but still works without noticeable delay

• Further "next" works ok.

[jmarshallnz]

Hmm, there doesn't seem to be anything wrong with the query, right? Mind running it in mysql directly and seeing if you get a bit more information from the error msg?

EDIT: Hmm, why isn't RANDOM() -> RAND() being detected...

[koying]

Exactly ;) I didn't dig further, but I can if you want...

[jmarshallnz]

Ah, I see the problem. The RANDOM() -> RAND() conversion is done only in vprepare, and we're using BuildSQL() which assumes pre-formatted.

[jmarshallnz]

Ok, should work now :)

[koying]

Yep. working fine and no slowdowns :)

[jmarshallnz]

Thanks :)

[veggiematts]

Hi !

I'm wondering if the proposed patch also fixes the issue for music party mode, or just for video party mode ?

[t-nelson]

It's not proposed, it's merged. Try any build from the last 10mo and you'll know whether or not it works.

FYI. Commenting on github spams ~50 dev inboxs. Please keep support requests, like this, to the forums in the future.