# Extended Protocol Packet Metadata SingleStore uses the same format of [column definition packet](https://dev.mysql.com/doc/dev/mysql-server/latest/page_protocol_com_query_response_text_resultset_column_definition.html) when communicating between the client and the server as the [MySQL protocol](https://dev.mysql.com/doc/dev/mysql-server/latest/PAGE_PROTOCOL.html). By default, packet metadata sent to the client consists of 12 bytes, which does not allow distinguishing non-MySQL protocol-compatible data types. Extending the packet metadata size allows the client to distinguish between data types that are not compatible with MySQL, such as `BSON` and `VECTOR`. Refer to [enum\_field\_types Reference](https://dev.mysql.com/doc/dev/mysql-server/latest/field__types_8h.html#a69e798807026a0f7e12b1d6c72374854) for a list of MySQL supported data types. By default, SingleStore does not send extended metadata in the protocol packet for backward compatibility. When extended metadata in the protocol packet is disabled (default behavior), `BSON` and `VECTOR` type columns are sent to the clients as `LONGBLOB` and `VARCHAR`, respectively. Refer to [Data Types](https://docs.singlestore.com/db/v9.1/reference/sql-reference/data-types.md) for more information on the respective data types. Extended protocol packet metadata is supported in SingleStore version 8.5.28 and later. **Note**: The MariaDB C library does not support extended metadata format. ## Enable Extended Metadata To enable sending extended metadata in the protocol packet for `BSON` and `VECTOR` data types: ```sql SET SESSION enable_extended_types_metadata = TRUE; ``` `enable_extended_types_metadata` is a session variable that can be set globally. SingleStore recommends configuring this engine variable for each session. ## Extended Metadata Format The packet metadata for extended types has the following structure: | Type | Name | Description | | ---------------- | ------------------------------ | ------------------------------------------------------------------------------------------------------------------------------ | | `string` | catalog | Catalog name. Currently, this value is always`"def"`. | | `string` | database | Database name | | `string` | table | Virtual table name | | `string` | org\_table | Physical table name | | `string` | name | Virtual column name | | `string` | org\_name | Physical column name | | `int` | | Length of the fixed length fields. This value is greater than or equal to 12 (0x0C) bytes. | | `int<2>` | character\_set | The column[character set](https://dev.mysql.com/doc/dev/mysql-server/latest/page_protocol_basic_character_set.html). | | `int<4>` | column\_length | Maximum length of the field in bytes. | | `int<1>` | type | Column[type](https://dev.mysql.com/doc/dev/mysql-server/latest/field__types_8h.html#details). | | `int<2>` | flags | [Column definition flags](https://dev.mysql.com/doc/dev/mysql-server/latest/group__group__cs__column__definition__flags.html). | | `int<1>` | decimals | Number of decimal places. | | `int<2>` | unused | Two unused zero-bytes. | | `int<1>` | type code of extended datatype | Type code of the extended type. This value is`2`for`VECTOR`data types and`1`for`BSON`types. | where, `lenenc` represents a length-encoded string. For `VECTOR` types, the protocol packet metadata contains the following additional bytes: | Type | Name | Description | | -------- | ------------------------- | ---------------------------------------- | | `int<4>` | number of vector elements | Dimension of the`VECTOR`type. | | `int<1>` | type of vector elements | The type of elements in the vector data. | ## For `VECTOR` Types For `VECTOR` types, the protocol packet metadata contains the following **6 bytes** in addition to the default 12 bytes: 1. **1 byte**: Specifies the type code. This value is `2` for `VECTOR` data types. 2. **4 bytes**: Specifies the dimension (number of elements) of the vector data. 3. **1 byte**: Specifies the type of elements in the vector data. It can have the following values based on the type of the vector elements: | Value | Vector Element Type | | ----- | ------------------- | | `1` | `F32` | | `2` | `F64` | | `3` | `I8` | | `4` | `I16` | | `5` | `I32` | | `6` | `I64` | For example, the protocol packet metadata for a `VECTOR(23)` type column (starting from the "Length of the fixed length field" byte) is: | Extended Types Disabled | Extended Types Enabled | | -------------------------------------- | ----------------------------------------------------------- | | 0c 3f 00 ff ff ff ff fd 90 00 00 00 00 | 12 3f 00 ff ff ff ff fd 90 00 00 00 00**02 17 00 00 00 01** | where the extended bytes represent the following: * `02`: Type code for `VECTOR` type. * `17 00 00 00`: Dimension (length) of the vector data, i.e., `23`. * `01`: Vector element type, i.e., `F32`. ## For `BSON` Types For `BSON` types, the protocol packet metadata contains **1 byte** in addition to the default 12 bytes. This additional byte specifies the type code, which is `1` for `BSON` types. *** Modified at: February 25, 2025 Source: [/db/v9.1/developer-resources/connect-with-application-development-tools/extended-protocol-packet-metadata/](https://docs.singlestore.com/db/v9.1/developer-resources/connect-with-application-development-tools/extended-protocol-packet-metadata/) (An index of the documentation is available at /llms.txt)