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Document ROW_GROUPS_PER_FILE option #2593

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Document ROW_GROUPS_PER_FILE option #2593

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16 changes: 16 additions & 0 deletions docs/data/parquet/tips.md
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Expand Up @@ -50,3 +50,19 @@ COPY
```

See the [Performance Guide on file formats](../../guides/performance/file_formats#parquet-file-sizes) for more tips.

### The `ROW_GROUPS_PER_FILE` Option

The `ROW_GROUPS_PER_FILE` parameter creates a new Parquet file if the current one has a specified number of row groups.

```sql
COPY
(FROM generate_series(100_000))
TO 'output-directory'
(FORMAT PARQUET, ROW_GROUP_SIZE 20_000, ROW_GROUPS_PER_FILE 2);
```

> If multiple threads are active, the number of row groups in a file may slightly exceed the specified number of row groups to limit the amount of locking – similarly to the behaviour of [`FILE_SIZE_BYTES`](../../sql/statements/copy#copy--to-options).
> However, if `PER_THREAD_OUTPUT` is set, only one thread writes to each file, and it becomes accurate again.

See the [Performance Guide on file formats](../../guides/performance/file_formats#parquet-file-sizes) for more tips.
1 change: 1 addition & 0 deletions docs/sql/statements/copy.md
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Expand Up @@ -175,6 +175,7 @@ The below options are applicable when writing `Parquet` files.
| `field_ids` | The `field_id` for each column. Pass `auto` to attempt to infer automatically. | `STRUCT` | (empty) |
| `row_group_size_bytes` | The target size of each row group. You can pass either a human-readable string, e.g., '2MB', or an integer, i.e., the number of bytes. This option is only used when you have issued `SET preserve_insertion_order = false;`, otherwise it is ignored. | `BIGINT` | `row_group_size * 1024` |
| `row_group_size` | The target size, i.e., number of rows, of each row group. | `BIGINT` | 122880 |
| `row_groups_per_file` | Create a new Parquet file if the current one has a specified number of row groups. If multiple threads are active, the number of row groups in a file may slightly exceed the specified number of row groups to limit the amount of locking – similarly to the behaviour of `file_size_bytes`. However, if `per_thread_output` is set, only one thread writes to each file, and it becomes accurate again. | `BIGINT` | (empty) |

Some examples of `FIELD_IDS` are:

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