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SHOW INDEXES

List all indexes defined on a Lance table.

Spark Extension Required

This feature requires the Lance Spark SQL extension to be enabled. See Spark SQL Extensions for configuration details.

Overview

The SHOW INDEXES command returns one row for each index on a Lance table. The information is retrieved using the Dataset.describeIndices method, and the output columns align with the attributes of org.lance.index.IndexDescription. Per-segment metadata is not listed individually; num_segments and size_bytes summarise it.

This command is useful for inspecting existing indexes, verifying index creation, and understanding the high-level properties of each index.

Syntax

SHOW INDEXES FROM multipartIdentifier;
SHOW INDEXES IN multipartIdentifier;
SHOW INDEX FROM multipartIdentifier;
SHOW INDEX IN multipartIdentifier;

multipartIdentifier can be a fully qualified table name (for example lance.db.users) or a shorter form depending on the current catalog and namespace configuration.

Examples

List indexes on a table

List all indexes on a Lance table lance.db.users:

SHOW INDEXES FROM lance.db.users;

You can also use the IN keyword or the singular INDEX spelling:

SHOW INDEX IN lance.db.users;

Output

The SHOW INDEXES command returns the following columns:

Column Type Description
name string Logical name of the index.
fields array List of column names included in the index.
index_type string Human-readable index type (for example btree).
num_indexed_fragments long Number of fragments fully or partially covered by the index.
num_indexed_rows long Approximate number of rows covered by the index.
num_unindexed_fragments long Number of fragments that are not yet indexed.
num_unindexed_rows long Approximate number of rows that are not yet covered by the index.
indexed_percent double Share of rows the index covers, as a percentage truncated to two decimals, so it never overstates coverage. Null for an empty table.
num_segments long Number of physical index segments backing this logical index.
size_bytes long Total size of all index files across the segments. Null if any segment predates index file size tracking.

Interpreting the Output

An indexed_percent below 100 means part of the table is not covered — either rows were appended since the index was last built, or OPTIMIZE rewrote fragments an index had covered. Rebuild with CREATE INDEX to restore full coverage.

num_segments reflects how the index was built: a distributed build produces one segment per parallel task. Queries search every segment, and Lance can only compact fragments covered by the identical set of segments, so a high count costs both query time and OPTIMIZE's ability to coalesce. Rebuilding with CREATE INDEX consolidates them.

Notes

  • The fields column returns the logical column names from the Lance schema, ordered according to the index definition.
  • Lance-maintained system indexes, including fragment-reuse and MemWAL indexes, are excluded from the output.
  • Row counts are approximate, so indexed_percent is a guide rather than an exact figure.

See Also

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CREATE INDEX