ALTER TABLE DETACH PARTITION

Makes partition data unavailable for reads and prepares partition directory for transportation. A partition detached by this SQL keyword can be "re-attached" using the complementary SQL keyword ALTER TABLE ATTACH PARTITION.

Syntax#

Flow chart showing the syntax of ALTER TABLE with DETACH LIST PARTITION keyword

Example#

To detach one or more partitions, let's assume table x with 3 partitions, 2019-02-01, 2019-02-02, and 2019-02-03:

  1. Detach two partitions using the SQL ALTER TABLE DETACH PARTITION command:

    ALTER TABLE x DETACH PARTITION LIST '2019-02-01', '2019-02-02';
    -- It is also possible to use WHERE clause to define the partition list:
    ALTER TABLE sensors DETACH PARTITION WHERE < '2019-02-03T00';
  2. Users can move the partition, for example, to an S3 bucket:

    cd /var/lib/questdb/db/x/
    tar cfz - '2019-02-01.detached' | aws s3 cp - s3://questdb-internal/blobs/20190201.tar.gz
    tar cfz - '2019-02-02.detached' | aws s3 cp - s3://questdb-internal/blobs/20190202.tar.gz

    The table directory is nested in the root directory. The root directory is set by cairo.root and is set to db by default. The detached partition files have the suffix .detached.

Limitation#

  • QuestDB does not compress partitions after detaching nor does it change partition format significantly. In most cases, compression will have to be done manually before partitions are transported to cold storage.
  • The operation does not support detaching:
    • An active (the last) partition.
    • The only partition in case of non-partitioned tables.

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