# `PARAMETER::` `TiDB Lightning` Task Parameter: `table-concurrency`
+ Section: **`[lightning]`**
+ Name: **`table-concurrency`**
+ Description: 
  + The maximum concurrency for data engines, each table is split into multiple "data engines" to store row data, this settings controls the maximum concurrent number for data engine
+ For example, assign 6 `RocksDB` engines for sorting `KV` pairs for table rows:
```
[lightning]
table-concurrency = 6
```
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The maximum concurrency number of `data engine` to be opened concurrently.

An engine is a `RocksDB` instance for sorting `KV` pairs. `TiDB Lightning` transfers data to `TiKV Importer` through engines. It first opens an engine, sends `KV` pairs to it (with no particular order), and finally closes the engine. The engine sorts the received `KV` pairs after it is closed. These closed engines can then be further uploaded to the `TiKV` stores for ingestion.

When a table is very large, its data is placed into multiple `data engines` to improve task pipelining. By default, a new `data engine` is opened for every `100 GB` of `SQL` data, which can be configured through the `batch-size` setting under `[mydumper]` section.

Similar to `index-concurrency`, it affects the memory and disk usage of `tikv-importer`.