# `PARAMETER::` `TiDB Lightning` Task Parameter: `index-concurrency`
+ Section: **`[lightning]`**
+ Name: **`index-concurrency`**
+ Description: 
  + The maximum concurrency for index engine, each table is split into one "index engine" to store indices, this settings controls the maximum concurrent number for index engine and which in turn it also configures the maximum number of tables to process at the same time
+ For example, assign 2 `RocksDB` engines for sorting `KV` pairs for indices:
```
[lightning]
index-concurrency = 2
```
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The maximum concurrency number of `index engine` to be opened concurrently.

Regardless of number of indices, every table is associated with exactly one `index engine`.

`TiDB Lightning` processes multiple `index engines` concurrently. Since every table has exactly one `index engine`, this also configures the maximum number of tables to process at the same time.

Each table is split into one "`index engine`" to store indices, this settings controls the maximum concurrent number for `index engine`.

It affects the memory and disk usage of `tikv-importer`.