Move cache to sqlite

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The current MusicCollection implementation is very slick, but very memory
intensive.  People with very large collections would have to set a very
large heap size to be able to use Harmonium at all.

I wonder if we could store less when parsing the cache at startup, and look
things up from the cache on-the-fly in more situations, so we don't have to
hold the whole collection in memory.

This would be a pretty major change, and decidedly not trivial.  It might
make sense to get an estimate how much heap memory is used per song in the
collection, so we could draw a correlation between library size and heap
size.  With this information we could better decide if it's worth taking
this on.

Storing the cache in something like sqlite might be worth exploring to help
with this and generally make the cache faster.

Original issue reported on code.google.com by ian.ol...@gmail.com on 24 Dec 2009 at 3:30

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Moving to sqlite would probably also let us avoid the startup scan, which is 
always
going to be slow for people with large collections. 
(http://tivocommunity.com/tivo-vb/showthread.php?p=7690267#post7690267)

Original comment by ian.ol...@gmail.com on 30 Dec 2009 at 3:10

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Original comment by ian.ol...@gmail.com on 1 Jan 2010 at 6:25

• Added labels: Reach

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Using sqlite would also make it easier to add more metadata, e.g. playcount, 
ratings,
etc.

Original comment by ian.ol...@gmail.com on 7 Jan 2010 at 4:21

• Changed title: Move cache to sqlite
• Added labels: Priority-Hopefully
• Removed labels: Priority-Maybe

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Original comment by ian.ol...@gmail.com on 6 Feb 2010 at 8:46

• Added labels: Milestone-Release1.0