[Fix] Implement efficient directory query in handleGetMusicDirectoryRequest() - #880
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JonnieCache wants to merge 3 commits into
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JonnieCache wants to merge 3 commits into
JonnieCache wants to merge 3 commits into
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Returns the releases held by the direct children of a directory in a single query, for callers that list a directory and need each child's release.
The subdirectory loop looked up each child's release separately, so listing a directory cost one query per child, each in its own nested transaction. Resolve them all up front instead.
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The problem
The current
handleGetMusicDirectoryRequest()function, the handler for the/getMusicDirectoryendpoint in the subsonic API does an N+1 query pattern when looking up the releases for the subdirectories of a queried directory. When querying a directory with N children, you get N additionalRelease::findqueries. Each gets their own nested db transaction. This is very slow.The change
This PR adds
Directory::findChildReleases()which returns all releases for direct children of a given directory in a single query.As this is intended as a unified query interface for both the subsonic API and my upcoming second attempt at the Folder Browsing UI, I return a vector of
ChildReleasestructs containing theReleaseas well as the count of releases found inside the directory. This so that the folder UI can direct-link to the release only if it's alone in its directory, whereas subsonic wants to link an arbitrary release even if there are several candidates.Performance
I measured on a raspberry pi 4 using the
Dockerfile-releasecontainer, calling/getMusicDirectorywith my real database file, with some large directories with a lot of subdirs. I observed a 1.26x mean speedup.I also noted that it's still very slow on the raspi, with the biggest dir going from 3253ms to 2780ms. This is because
createAlbumNode()runs 8 further database queries per-release to retrieve Genre, Mood and so on, essentially the same problem this PR solves but more so. The solution would be to do all of this in one large chain of JOINs and have sqlite sort it all out inside one query. This will be a lot faster.