update tiflash doc add dt_compression_method and dt_compression_level…

… config (#7822)
pingcap · Mar 23, 2022 · 20150b6 · 20150b6
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diff --git a/tiflash/tiflash-command-line-flags.md b/tiflash/tiflash-command-line-flags.md
@@ -29,8 +29,8 @@ This document introduces the command-line flags that you can use when you launch
     - `--version`: The version of DTFile. The value options are `1` and `2` (default). `1` is the old version, and `2` is the version corresponding to the new checksum.
     - `--algorithm`: The hash algorithm used for data validation. The value options are `xxh3` (default), `city128`, `crc32`, `crc64`, and `none`. This parameter is effective only when `version` is `2`.
     - `--frame`: The size of the validation frame. The default value is `1048576`. This parameter is effective only when `version` is `2`.
-    - `--compression`: The target compression algorithm. The value options are `lz4` (default), `lz4hc`, `zstd`, and `none`.
-    - `--level`: The target compression level. The default value is `-1`, which means automatic mode. The value range varies with different compression algorithms.
+    - `--compression`: The target compression algorithm. The value options are `LZ4` (default), `LZ4HC`, `zstd`, and `none`.
+    - `--level`: The target compression level. If not specified, the recommended compression level is used by default according to the compression algorithm. If `compression` is set to `LZ4` or `zstd`, the default level is 1. If `compression` is set to `LZ4HC`, the default level is 9. 
     - `--config-file`: The configuration file of `dttool migrate` is the same as the [configuration file of `server`](/tiflash/tiflash-command-line-flags.md#server---config-file). When you use the configuration file, exit the local TiFlash server instance. For more information, see `--imitative`.
     - `--file-id`: The ID of the DTFile. For example, the ID of the DTFile `dmf_123` is `123`.
     - `--workdir`: The parent directory of `dmf_xxx`.

diff --git a/tiflash/tiflash-configuration.md b/tiflash/tiflash-configuration.md
@@ -193,6 +193,10 @@ delta_index_cache_size = 0
     batch_cop_pool_size = 0
     ## New in v5.4.0. This item enables or disables the elastic thread pool feature, which significantly improves CPU utilization in high concurrency scenarios of TiFlash. The default value is false. The elastic thread pool feature is experimental and not recommended for production environments.
     enable_elastic_threadpool = false
+    # Compression algorithm of the TiFlash storage engine. The value can be LZ4, zstd, or LZ4HC, and is case-insensitive. By default, LZ4 is used.
+    dt_compression_method = "LZ4"
+    # Compression level of the TiFlash storage engine. The default value is 1. It is recommended that you set this value to 1 if dt_compression_method is LZ4, -1 (smaller compression rate, but better read performance) or 1 if dt_compression_method is zstd, and 9 if dt_compression_method is LZ4HC.
+    dt_compression_level = 1
 
 ## Security settings take effect starting from v4.0.5.
 [security]