Lower zstd blockDocCount for best_speed from 128 to 96 (#112098)

Query latencies are more important for best speed use cases. Zstd stored fields have shown some increase in query latencies when limited number of stored field data is fetched (in case of get by id like queries). By decreasing the blockDocCount we try to reduce these latencies at the cost of using a little bit more storage.

Based on the shared results below, setting blockDocCount to 96.

Note that zstd is still behind a feature flag and this is the last things we like to tune before removing the feature flag. In all other cases zstd has shown to be the better trade of compared to lz4 and deflate (which get used depending on index.codec setting).

After merging this change, we should monitor the nightly benchmarks and see the total effect before removing the feature flag.

Author: martijnvg

server/src/main/java/org/elasticsearch/index/codec/zstd/Zstd814StoredFieldsFormat.java

@@ -47,7 +47,7 @@ public final class Zstd814StoredFieldsFormat extends Lucene90CompressingStoredFi
     public static final String MODE_KEY = Zstd814StoredFieldsFormat.class.getSimpleName() + ".mode";
 
     public enum Mode {
-        BEST_SPEED(0, BEST_SPEED_BLOCK_SIZE, 128),
+        BEST_SPEED(0, BEST_SPEED_BLOCK_SIZE, 96),
         BEST_COMPRESSION(3, BEST_COMPRESSION_BLOCK_SIZE, 2048);
 
         final int level, blockSizeInBytes, blockDocCount;

server/src/test/java/org/elasticsearch/index/codec/CodecTests.java

@@ -58,7 +58,7 @@ public void testDefault() throws Exception {
         assumeTrue("Only when zstd_stored_fields feature flag is enabled", CodecService.ZSTD_STORED_FIELDS_FEATURE_FLAG.isEnabled());
         Codec codec = createCodecService().codec("default");
         assertEquals(
-            "Zstd814StoredFieldsFormat(compressionMode=ZSTD(level=0), chunkSize=14336, maxDocsPerChunk=128, blockShift=10)",
+            "Zstd814StoredFieldsFormat(compressionMode=ZSTD(level=0), chunkSize=14336, maxDocsPerChunk=96, blockShift=10)",
             codec.storedFieldsFormat().toString()
         );
     }