op-guide: add description for txn-local-latches (#535)

* tools: add drainer output

via: pingcap/docs-cn#795

* op-guide: add description for txn-local-latches

via: pingcap/docs-cn#776

* op-guide: address comment

Via: #535

Author: yikeke

op-guide/tidb-config-file.md

@@ -201,3 +201,17 @@ The Plan Cache configuration of the `prepare` statement.
 - The maximum timeout time when executing a transaction commit
 - Default: 41s
 - It is required to set this value larger than twice of the Raft election timeout time
+
+### txn-local-latches
+
+Configuration about the transaction latch. It is recommended to enable it when many local transaction conflicts occur.
+
+### `enable`
+
+- To enable
+- Default: false
+
+### `capacity`
+
+- The number of slots corresponding to Hash, which automatically adjusts upward to an exponential multiple of 2. Each slot occupies 32 Bytes of memory. If set too small, it might result in slower running speed and poor performance in the scenario where data writing covers a relatively large range (such as importing data).
+- Default: 1024000

tools/tidb-binlog-kafka.md

@@ -98,15 +98,15 @@ cd tidb-binlog-latest-linux-amd64
     ```
     [syncer]
     db-type = "kafka"
-
+    
     # when db-type is kafka, you can uncomment this to config the down stream kafka, or it will be the same kafka addrs where drainer pulls binlog from.
     # [syncer.to]
     # kafka-addrs = "127.0.0.1:9092"
     # kafka-version = "0.8.2.0"
     ```
-
+    
     The data which outputs to kafka follows the binlog format sorted by ts and defined by protobuf. See [driver](https://github.com/pingcap/tidb-tools/tree/master/tidb_binlog/driver) to access the data and sync to the down stream.
-
+    
 - Deploy Kafka and ZooKeeper cluster before deploying TiDB-Binlog. Make sure that Kafka is 0.9 version or later.
 
 #### Recommended Kafka cluster configuration