Comment by Paul-E

Comment by Paul-E 18 hours ago

That's pretty neat!

I did something similar. I build a tool[1] to import the Project Arctic Shift dumps[2] of reddit into sqlite. It was mostly an exercise to experiment with Rust and SQLite (HN's two favorite topics). If you don't build a FTS5 index and import without WAL (--unsafe-mode), import of every reddit comment and submission takes a bit over 24 hours and produces a ~10TB DB.

SQLite offers a lot of cool json features that would let you store the raw json and operate on that, but I eschewed them in favor of parsing only once at load time. THat also lets me normalize the data a bit.

I find that building the DB is pretty "fast", but queries run much faster if I immediately vacuum the DB after building it. The vacuum operation is actually slower than the original import, taking a few days to finish.

[1] https://github.com/Paul-E/Pushshift-Importer

[2] https://github.com/ArthurHeitmann/arctic_shift/blob/master/d...

Xyra 5 hours ago

Holy cow, I didn't know getting reddit was that straightforward. I am building public readonly-SQL+vector databases optimized for exploring high-quality public commons with Claude Code (https://exopriors.com/scry), I so cannot wait until some funding source comes in and I can upgrade to a $1500/month Hetzner server and pay the ~$1k to embed all that.

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s_ting765 18 hours ago

You could check out SQLite's auto_vacuum which reclaims space without rebuilding the entire db https://sqlite.org/pragma.html#pragma_auto_vacuum

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Paul-E 14 hours ago

I haven't tested that, so I'm not sure if it would work. The import only inserts rows, it doesn't delete, so I don't think that is the cause of fragmentation. I suspect this line in the vacuum docs:
> The VACUUM command may change the ROWIDs of entries in any tables that do not have an explicit INTEGER PRIMARY KEY.
means SQLite does something to organize by rowid and that this is doing most of the work.
Reddit post/comment IDs are 1:1 with integers, though expressed in a different base that is more friendly to URLs. I map decoded post/comment IDs to INTEGER PRIMARY KEYs on their respective tables. I suspect the vacuum operation sorts the tables by their reddit post ID and something about this sorting improves tables scans, which in turn helps building indices quickly after standing up the DB.

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