mysql2elasticsearch 不管怎么配置setting，job都只会被切分为1个task，求解答

我设置了channel，也配置了splitPK(bigint类型的主键)，都只会有1个task

```
{
"content":[
{
"reader":{
"name":"mysqlreader",
"parameter":{
"column":[
"id",
"label1",
"label2"
],
"connection":[
{
"jdbcUrl":[
"jdbc:mysql://10.20.*.*:33061/db_table?useUnicode=true&characterEncoding=utf-8"
],
"table":[
"mysql2es"
]
}
],
"password":"***********",
"splitPK":"id",
"username":"root"
}
},
"writer":{
"name":"elasticsearchwriter",
"parameter":{
"accessId":"elastic",
"accessKey":"***********",
"batchSize":1000,
"cleanup":true,
"column":[
{
"name":"id",
"type":"long"
},
{
"name":"label1",
"type":"integer"
},
{
"name":"label2",
"type":"integer"
}
],
"discovery":false,
"dynamic":false,
"endpoint":"http://10.20.*.*:9400",
"index":"mysql2es",
"settings":{
"index":{
"number_of_replicas":1,
"number_of_shards":3,
"refresh_interval":"10s"
}
},
"type":"_doc"
}
}
}
],
"setting":{
"speed":{
"channel":3
}
}
}

2022-10-26 10:43:01.565 [job-0] INFO ElasticSearchWriter$Job - unified version: 1666752181565
2022-10-26 10:43:01.570 [job-0] INFO ElasticSearchWriter$Job - [{"array":false,"combineFieldsValueSeparator":"-","dstArray":false,"jsonArray":false,"name":"id","origin":false,"type":"long"},{"array":false,"combineFieldsValueSeparator":"-","dstArray":false,"jsonArray":false,"name":"label1","origin":false,"type":"integer"},{"array":false,"combineFieldsValueSeparator":"-","dstArray":false,"jsonArray":false,"name":"label2","origin":false,"type":"integer"}]
2022-10-26 10:43:01.570 [job-0] INFO ElasticSearchWriter$Job - index:[mysql2es], type:[_doc], mappings:[{"properties":{"id":{"type":"long"},"label1":{"type":"integer"},"label2":{"type":"integer"}}}]
2022-10-26 10:43:01.577 [job-0] INFO ElasticSearchClient - begin GetMapping for index: mysql2es
2022-10-26 10:43:01.581 [job-0] INFO ElasticSearchWriter$Job - the mappings for old index is: {"id":{"type":"long"},"label1":{"type":"integer"},"label2":{"type":"integer"}}
2022-10-26 10:43:01.582 [job-0] INFO ElasticSearchClient - begin GetSettings for index: mysql2es
2022-10-26 10:43:01.586 [job-0] INFO ElasticSearchWriter$Job - merge1 settings:{"mysql2es":{"settings":{"index":{"routing":{"allocation":{"include":{"_tier_preference":"data_content"}}},"refresh_interval":"10s","number_of_shards":"3","provided_name":"mysql2es","creation_date":"1666751769822","number_of_replicas":"1","uuid":"LjMiDqIlR0-vUKlnCNNZdA","version":{"created":"7120099"}}}}}, settingsCache:null, includeSettings:{"number_of_replicas":"1","number_of_shards":"3"}
2022-10-26 10:43:01.587 [job-0] INFO ElasticSearchClient - delete index mysql2es
2022-10-26 10:43:01.891 [job-0] INFO ElasticSearchClient - delete index mysql2es success
2022-10-26 10:43:01.891 [job-0] INFO ElasticSearchWriter$Job - merge2 settings:{"index":{"number_of_replicas":1,"number_of_shards":3,"refresh_interval":"10s"}}, settingsCache:{"index":{"number_of_replicas":1,"number_of_shards":3,"refresh_interval":"10s"},"number_of_replicas":"1","number_of_shards":"3"}
2022-10-26 10:43:01.894 [job-0] WARN ElasticSearchClient - null
2022-10-26 10:43:01.894 [job-0] WARN ElasticSearchClient - IndicesExists got ResponseCode: 404 ErrorMessage: 404 Not Found
2022-10-26 10:43:01.894 [job-0] INFO ElasticSearchClient - create index mysql2es
2022-10-26 10:43:02.060 [job-0] INFO ElasticSearchClient - create mysql2es index success
2022-10-26 10:43:02.061 [job-0] INFO ElasticSearchClient - create mappings for mysql2es {"properties":{"id":{"type":"long"},"label1":{"type":"integer"},"label2":{"type":"integer"}}}
2022-10-26 10:43:02.110 [job-0] INFO ElasticSearchClient - index mysql2es put mappings success
2022-10-26 10:43:02.111 [job-0] INFO JobContainer - jobContainer starts to do split ...
2022-10-26 10:43:02.111 [job-0] INFO JobContainer - Job set Channel-Number to 3 channels.
2022-10-26 10:43:02.115 [job-0] INFO JobContainer - DataX Reader.Job [mysqlreader] splits to [1] tasks.
2022-10-26 10:43:02.116 [job-0] INFO JobContainer - DataX Writer.Job [elasticsearchwriter] splits to [1] tasks.
2022-10-26 10:43:02.125 [job-0] INFO JobContainer - jobContainer starts to do schedule ...
2022-10-26 10:43:02.128 [job-0] INFO JobContainer - Scheduler starts [1] taskGroups.
2022-10-26 10:43:02.130 [job-0] INFO JobContainer - Running by standalone Mode.
2022-10-26 10:43:02.135 [taskGroup-0] INFO TaskGroupContainer - taskGroupId=[0] start [1] channels for [1] tasks.
2022-10-26 10:43:02.138 [taskGroup-0] INFO Channel - Channel set byte_speed_limit to -1, No bps activated.
2022-10-26 10:43:02.138 [taskGroup-0] INFO Channel - Channel set record_speed_limit to -1, No tps activated.
2022-10-26 10:43:02.150 [taskGroup-0] INFO TaskGroupContainer - taskGroup[0] taskId[0] attemptCount[1] is started
2022-10-26 10:43:02.152 [0-0-0-reader] INFO CommonRdbmsReader$Task - Begin to read record by Sql: [select id,label1,label2 from mysql2es
] jdbcUrl:[jdbc:mysql://10.20.35.85:33061/sx_dmp_jres?useUnicode=true&characterEncoding=utf-8&yearIsDateType=false&zeroDateTimeBehavior=convertToNull&tinyInt1isBit=false&rewriteBatchedStatements=true].
2022-10-26 10:43:02.155 [0-0-0-writer] INFO ElasticSearchWriter$Job - columnList: [{"array":false,"combineFieldsValueSeparator":"-","dstArray":false,"jsonArray":false,"name":"id","origin":false,"type":"long"},{"array":false,"combineFieldsValueSeparator":"-","dstArray":false,"jsonArray":false,"name":"label1","origin":false,"type":"integer"},{"array":false,"combineFieldsValueSeparator":"-","dstArray":false,"jsonArray":false,"name":"label2","origin":false,"type":"integer"}]
2022-10-26 10:43:02.155 [0-0-0-writer] INFO ElasticSearchWriter$Job - Task will use elasticsearch auto generated _id property
2022-10-26 10:43:02.156 [0-0-0-writer] INFO AbstractJestClient - Setting server pool to a list of 1 servers: [http://10.20.32.117:9400]
2022-10-26 10:43:02.157 [0-0-0-writer] INFO JestClientFactory - Using multi thread/connection supporting pooling connection manager
2022-10-26 10:43:02.158 [0-0-0-writer] INFO JestClientFactory - Using default GSON instance
2022-10-26 10:43:02.158 [0-0-0-writer] INFO JestClientFactory - Node Discovery disabled...
2022-10-26 10:43:02.158 [0-0-0-writer] INFO JestClientFactory - Idle connection reaping disabled...

Reproduce the supplied job in standalone mode and start with the JobContainer split stage, then trace the mysqlreader splitPK handling and the elasticsearchwriter task split shown in the logs. Compare the configured channel count with the reader and writer split results; done means the cause of the single task is identified and the expected configuration or behavior is documented.

Written by the indexing model from the issue text.