[doc] Add doc for precommit-compact

Author: JingsongLi

docs/content/append-table/streaming.md

@@ -30,7 +30,20 @@ You can streaming write to the Append table in a very flexible way through Flink
 Flink, using it like a queue. The only difference is that its latency is in minutes. Its advantages are very low cost
 and the ability to push down filters and projection.
 
-## Automatic small file merging
+## Pre small files merging
+
+Pre means that this compact occurs before committing files to the snapshot.
+
+If Flink's checkpoint interval is short (for example, 30 seconds), each snapshot may produce lots of small changelog
+files. Too many files may put a burden on the distributed storage cluster.
+
+In order to compact small changelog files into large ones, you can set the table option `precommit-compact = true`.
+Default value of this option is false, if true, it will add a compact coordinator and worker operator after the writer
+operator, which copies changelog files into large ones.
+
+## Post small files merging
+
+Post means that this compact occurs after committing files to the snapshot.
 
 In streaming writing job, without bucket definition, there is no compaction in writer, instead, will use
 `Compact Coordinator` to scan the small files and pass compaction task to `Compact Worker`. In streaming mode, if you

docs/content/primary-key-table/changelog-producer.md

@@ -138,6 +138,6 @@ For `input`, `lookup`, `full-compaction` 'changelog-producer'.
 If Flink's checkpoint interval is short (for example, 30 seconds) and the number of buckets is large, each snapshot may
 produce lots of small changelog files. Too many files may put a burden on the distributed storage cluster.
 
-In order to compact small changelog files into large ones, you can set the table option `changelog.precommit-compact = true`.
+In order to compact small changelog files into large ones, you can set the table option `precommit-compact = true`.
 Default value of this option is false, if true, it will add a compact coordinator and worker operator after the writer
 operator, which copies changelog files into large ones.