[LUCENE-10004] Delete unnecessary flush in Lucene90CompressingStoredFieldsWriter.copyChunks() to reduce dirty chunks

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Not A Problem
• Affects Version/s: 8.8.2
• Component/s: core/codecs
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: kkewwei
• Created: 15/Jun/21 04:47
• Updated: 28/Aug/22 16:23
• Resolved: 18/Jun/21 12:38

Description

In CompressingStoredFieldsWriter.merge(): if the segment meet the following conditions:

else if (matchingFieldsReader.getCompressionMode() == compressionMode && 
                 matchingFieldsReader.getChunkSize() == chunkSize && 
                 matchingFieldsReader.getPackedIntsVersion() ==PackedInts.VERSION_CURRENT &&
                 liveDocs == null &&
                 !tooDirty(matchingFieldsReader)) { 
       ......
       // flush any pending chunks
        if (numBufferedDocs > 0) {
          flush();
          numDirtyChunks++; // incomplete: we had to force this flush
        }
       ......
}

We will copy the the all chunk to the new fdt, before copying the chunk, we will flush the buffer docs if numBufferedDocs >0, but the flush is unnecessary.

The bufferedDocs in memory have nothing to do with copyChunk. We just need to ensure that it will be flush at the end of merge(In finish()).