> For the complete documentation index, see [llms.txt](https://mariadb.com/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mariadb.com/docs/server/reference/sql-structure/vectors/information-schema-vector_indexes-table.md). # Information Schema VECTOR\_INDEXES Table The Information Schema VECTOR\_INDEXES table reports the size, node counts and cache usage of each MHNSW vector index. {% hint style="info" %} This table is available from [MariaDB 13.1](https://jira.mariadb.org/browse/MDEV-34805). {% endhint %} The [Information Schema](/docs/server/reference/system-tables/information-schema.md) `VECTOR_INDEXES` table reports the size, node counts and cache usage of each [vector index](/docs/server/reference/sql-structure/vectors.md) in the server. It holds one row per vector index, which means one row per table, because a table can have at most one vector index. The table is provided by the built-in `VECTOR_INDEXES` Information Schema plugin, which ships alongside the `mhnsw` plugin and is available in a default build. Its [plugin maturity](/docs/server/reference/plugins/plugin-overview.md) is beta in MariaDB 13.1. It contains the following columns: | Column | Type | Description | | ------------------ | --------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | TABLE\_CATALOG | `varchar(64)` | Always `def`. | | TABLE\_SCHEMA | `varchar(64)` | Database containing the indexed table. | | TABLE\_NAME | `varchar(64)` | Name of the indexed table. | | INDEX\_NAME | `varchar(64)` | Name of the vector index. | | VECTOR\_DIMENSIONS | `int(10) unsigned` | Number of dimensions of the indexed [VECTOR](/docs/server/reference/sql-structure/vectors/vector.md) column. | | INDEX\_SIZE | `bigint(19) unsigned` | On-disk size of the graph table in bytes, that is its data length plus its index length. `NULL` if the graph table cannot be opened. | | TOTAL\_NODES | `bigint(19) unsigned` | Number of rows the storage engine reports for the graph table, each row being one node of the graph. See [Accuracy of the node counts](#accuracy-of-the-node-counts) below. | | CACHED\_NODES | `bigint(19) unsigned` | Number of graph nodes currently held in the index cache. `0` while the index is not cached. | | DELETED\_ROWS | `bigint(19) unsigned` | Estimated number of nodes in the graph that no longer have a row in the table, computed as `TOTAL_NODES` minus the number of rows the engine reports for the table, and never negative. `NULL` if the graph table cannot be opened. | | SUBDIST\_ENABLED | `varchar(3)` | Whether the partial-distance optimization is in use: `YES`, `NO`, or `NULL` while the server has not yet gathered enough statistics to decide. See [SUBDIST\_ENABLED](#subdist_enabled) below. | | MEMORY\_SIZE | `bigint(19) unsigned` | Memory currently allocated for the index cache, in bytes. `0` while the index is not cached. | ## Example For a table with 1000 rows, after a vector search has populated the index cache: ```sql SELECT * FROM INFORMATION_SCHEMA.VECTOR_INDEXES WHERE TABLE_NAME = 't'\G *************************** 1. row *************************** TABLE_CATALOG: def TABLE_SCHEMA: test TABLE_NAME: t INDEX_NAME: v VECTOR_DIMENSIONS: 2 INDEX_SIZE: 229376 TOTAL_NODES: 1000 CACHED_NODES: 225 DELETED_ROWS: 0 SUBDIST_ENABLED: NO MEMORY_SIZE: 4194176 ``` ## Privileges A vector index is only listed if the connection has a privilege on the indexed table, or a column-level privilege on the indexed vector column itself. A privilege on some other column of the table is not enough: ```sql GRANT SELECT (id) ON db.t TO 'u'@'localhost'; -- the index on db.t.v is not listed GRANT SELECT (v) ON db.t TO 'u'@'localhost'; -- the index on db.t.v is listed ``` ## Cache Usage `CACHED_NODES` and `MEMORY_SIZE` describe the in-memory copy of the graph, not the index itself, and both read `0` until the cache is populated. Whether an operation populates it depends on the storage engine: with InnoDB, `INSERT` alone leaves the cache empty and the first vector search fills it, while Aria and MyISAM already cache nodes while rows are inserted. Flushing the table with [FLUSH TABLES](/docs/server/reference/sql-statements/administrative-sql-statements/flush-commands/flush.md) discards the cache, so both columns fall back to `0` until the index is used again. `MEMORY_SIZE` is capped per index by [mhnsw\_max\_cache\_size](/docs/server/reference/sql-structure/vectors/vector-system-variables.md#mhnsw_max_cache_size). Because the vector index cache is not instrumented in the [Performance Schema](/docs/server/reference/system-tables/performance-schema.md), this column is the only way to see how much memory an individual vector index is using. ## Accuracy of the Node Counts `TOTAL_NODES` and, because it is derived from it, `DELETED_ROWS` are taken from the storage engine's row counts, and are therefore only as accurate as the engine's statistics. For InnoDB, both are estimates and can be far off: a table that has never had a row deleted can report thousands of deleted rows, and `ANALYZE TABLE` or a higher [innodb\_stats\_persistent\_sample\_pages](/docs/server/server-usage/storage-engines/innodb/innodb-system-variables.md#innodb_stats_persistent_sample_pages) does not improve them. Aria and MyISAM keep exact row counts and report exact values. `INDEX_SIZE` covers the graph table only, so it does not match [INFORMATION\_SCHEMA.TABLES](/docs/server/reference/system-tables/information-schema/information-schema-tables/information-schema-tables-table.md)`.INDEX_LENGTH` for a table that has other indexes, such as a primary key. ## SUBDIST\_ENABLED For high-dimensional vectors, MariaDB can compute a distance over the first 192 dimensions only and use it as a lower bound, skipping the full computation when that bound is already too large to be a candidate. This optimization is only eligible for vectors of 384 dimensions or more, and MariaDB decides whether to use it from statistics gathered while the index is searched. `SUBDIST_ENABLED` reports the outcome: * `NO` — the optimization is not in use, either because the vector has fewer than 384 dimensions, or because the collected statistics showed it would not be reliable for this data. * `YES` — the optimization is in use. * `NULL` — the vector has 384 dimensions or more, but the server has not yet seen enough searches to decide. ## See Also * [Vector Overview](/docs/server/reference/sql-structure/vectors/vector-overview.md) * [CREATE TABLE with Vectors](/docs/server/reference/sql-structure/vectors/create-table-with-vectors.md) * [Vector System Variables](/docs/server/reference/sql-structure/vectors/vector-system-variables.md) *This page is licensed: CC BY-SA / Gnu FDL* {% @marketo/form formId="4316" %}