compute: rename pool spill-threads dyncfg to column_paged_batcher_spill_worker_count

The prior name was registered in LaunchDarkly with the wrong data type,
and LD does not allow changing a parameter's type after creation; a
fresh name lets the flag be recreated correctly. Default and semantics
unchanged.

Author: DAlperin

src/compute-types/src/dyncfgs.rs

@@ -138,8 +138,8 @@ pub const COLUMN_PAGED_BATCHER_USE_POOL: Config<bool> = Config::new(
 /// rates. Thread spawning is once per process: raising the value later has
 /// no effect beyond re-enabling, and lowering it to zero falls back to
 /// inline eviction while spawned threads idle.
-pub const COLUMN_PAGED_BATCHER_POOL_SPILL_THREADS: Config<usize> = Config::new(
-    "column_paged_batcher_pool_spill_threads",
+pub const COLUMN_PAGED_BATCHER_SPILL_WORKER_COUNT: Config<usize> = Config::new(
+    "column_paged_batcher_spill_worker_count",
     2,
     "Buffer-pool spill threads for off-worker eviction I/O; 0 evicts inline on the caller.",
 );
@@ -566,5 +566,5 @@ pub fn all_dyncfgs(configs: ConfigSet) -> ConfigSet {
         .add(&COLUMN_PAGED_BATCHER_LZ4)
         .add(&COLUMN_PAGED_BATCHER_SWAP_PAGEOUT)
         .add(&COLUMN_PAGED_BATCHER_USE_POOL)
-        .add(&COLUMN_PAGED_BATCHER_POOL_SPILL_THREADS)
+        .add(&COLUMN_PAGED_BATCHER_SPILL_WORKER_COUNT)
 }

src/compute/src/compute_state.rs

@@ -328,7 +328,7 @@ impl ComputeState {
 
             let enabled = ENABLE_COLUMN_PAGED_BATCHER_SPILL.get(config);
             let use_pool = COLUMN_PAGED_BATCHER_USE_POOL.get(config);
-            let spill_threads = COLUMN_PAGED_BATCHER_POOL_SPILL_THREADS.get(config);
+            let spill_threads = COLUMN_PAGED_BATCHER_SPILL_WORKER_COUNT.get(config);
             let codec = COLUMN_PAGED_BATCHER_LZ4.get(config).then_some(Codec::Lz4);
             let swap_pageout = COLUMN_PAGED_BATCHER_SWAP_PAGEOUT.get(config);