mikemccand commented on issue #12542:
URL: https://github.com/apache/lucene/issues/12542#issuecomment-1711608900
Digging into this a bit, I think I found some silly performance bugs in our
current FST impl:
* We seem to create a `PagedGrowableWriter` with [page size 128 MB
here](https://github.com/apache/lucene/blob/main/lucene/core/src/java/org/apache/lucene/util/fst/NodeHash.java#L34),
meaning even when building a small FST, we are allocating at least 128 MB
pages?
* When we rehash, we create a new `PagedGrowableWriter`, with too small
estimated `bitsRequired` [since we pass `count` (the number of nodes in the
hash) instead of the most recently added `long
node`](https://github.com/apache/lucene/blob/main/lucene/core/src/java/org/apache/lucene/util/fst/NodeHash.java#L182).
We are actually storing the `long node` values, so it really should be `node`
not `count`. The effect of this is we make `PagedGrowableWriter` work harder
than necessary to reallocate when we store the next `node` that doesn't fit in
that `bitsRequired`.
I'll try to get the LRU hash working, but if that takes too long, we should
separately fix these performance bugs (if I'm right that these are really
bugs!).
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