fix: use new Compressor::rebuild_from for FSST pushdown (#2708)

The previous implementation of FSST comparison pushdown relied on
rebuilding a compressor by reinserting symbols one-by-one into the
CompressorBuilder, and then building it.

That doesn't work, for reasons described in the description at
spiraldb/fsst#84.

We use the new `rebuild_from` API on fsst compressor to build a new
compressor that is guaranteed to preserve symbol table ordering, and
thus guarantee equal compression outputs.

Author: a10y

Cargo.lock

@@ -93,7 +93,7 @@ fastlanes = "0.1.8"
 flatbuffers = "25"
 flexbuffers = "25"
 flume = "0.11"
-fsst-rs = "0.5.1"
+fsst-rs = "0.5.2"
 futures = { version = "0.3.31", default-features = false }
 futures-executor = "0.3.31"
 futures-util = "0.3.31"

Cargo.toml

@@ -68,14 +68,7 @@ fn compare_fsst_constant(
         return Ok(None);
     }
 
-    let symbols = left.symbols();
-    let symbol_lens = left.symbol_lengths();
-
-    let mut compressor = fsst::CompressorBuilder::new();
-    for (symbol, symbol_len) in symbols.iter().zip(symbol_lens.iter()) {
-        compressor.insert(*symbol, *symbol_len as usize);
-    }
-    let compressor = compressor.build();
+    let compressor = fsst::Compressor::rebuild_from(left.symbols(), left.symbol_lengths());
 
     let encoded_scalar = match left.dtype() {
         DType::Utf8(_) => {