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    PolarDB:Query the storage usage of IMCI

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    PolarDB:Query the storage usage of IMCI

    Last Updated:Mar 30, 2026

    Query the INFORMATION_SCHEMA.IMCI_INDEX_SPACE table to check how much storage your In-Memory Column Indexes (IMCIs) are using — at the table, database, or cluster level.

    Supported versions

    • PolarDB for MySQL 8.0.1, revision version 8.0.1.1.44 or later

    • PolarDB for MySQL 8.0.2, revision version 8.0.2.2.25 or later

    Query IMCI storage usage

    Before running any query against INFORMATION_SCHEMA.IMCI_INDEX_SPACE, run the following statement to minimize metadata overhead and improve query performance:

    SET IMCI_I_S_SKIP_DD_OPEN = ON;

    Query by table

    SELECT
  SCHEMA_NAME, TABLE_NAME, TOTAL_SPACE
FROM
  INFORMATION_SCHEMA.IMCI_INDEX_SPACE
WHERE SCHEMA_NAME = 'TEST' AND TABLE_NAME = 'TEST';

    Query by database

    SELECT
  SCHEMA_NAME, SUM(TOTAL_SPACE)
FROM
  INFORMATION_SCHEMA.IMCI_INDEX_SPACE
WHERE SCHEMA_NAME = 'TEST';

    Query all IMCIs in the cluster

    SELECT
  SUM(TOTAL_SPACE)
FROM
  INFORMATION_SCHEMA.IMCI_INDEX_SPACE;

    Column reference

    INFORMATION_SCHEMA.IMCI_INDEX_SPACE returns the following columns:

    Column Description
    SCHEMA_NAME Name of the database.
    TABLE_NAME Name of the table.
    TABLE_ID ID of the table.
    INDEX_ID ID of the IMCI.
    TOTAL_SPACE Total storage used by all IMCI files. Unit: bytes.
    INDEX_META_SPACE Storage used by the IMCI metadata file. Unit: bytes.
    NCI_SPACE Storage used by the mapping file that defines the mapping between the IMCI and the rowstore primary keys. Unit: bytes.
    PACK_DATA_SPACE Storage used by the IMCI pack file. Unit: bytes.
    FULL_PACKMETA_SPACE Storage used by the full pack metadata file. Unit: bytes.
    PARTIAL_PACKMETA_SPACE Storage used by the partial pack metadata file. Unit: bytes.
    MASK_SPACE Storage used by the visibility tag file. Unit: bytes.

    Key metrics for capacity planning

    PACK_DATA_SPACE and NCI_SPACE are the primary indicators of IMCI storage consumption:

    • PACK_DATA_SPACE: Storage used by the IMCI pack file. This is a key metric for measuring IMCI storage usage.

    • NCI_SPACE: Storage used by the mapping file that defines the mapping between the IMCI and the rowstore primary keys. This is a key metric for measuring IMCI storage usage.

    Monitor these two columns to assess actual IMCI footprint and plan capacity.