Routinely Recreating an Index

Background

When data deletion is repeatedly performed in the database, index keys will be deleted from the index pages, resulting in index bloat. Recreating an index routinely improves query efficiency.

The database supports B-tree indexes. Recreating a B-tree index routinely helps improve query efficiency.

• If a large amount of data is deleted, index keys on the index pages will be deleted. But index pages will not be directly deleted, that is the number of index pages will not decrease, then index bloat occurs. Recreating an index helps reclaim wasted space.
• In a newly created index, pages with adjacent logical structures tend to have adjacent physical structures. Therefore, a new index achieves a higher access speed than an index that has been updated for multiple times.

Methods

Use either of the following two methods to recreate an index:

• Run the DROP INDEX statement to delete the index and run the CREATE INDEX statement to create an index.

  When you delete an index, a temporary exclusive lock is added in the parent table to block related read/write operations. During index creation, the write operation is locked, whereas the read operation is not locked and can use only sequential scans.

• Run REINDEX to recreate an index.

  • When you run the REINDEX TABLE statement to recreate an index, an exclusive lock is added to block related read/write operations.
  • When you run the REINDEX INTERNAL TABLE statement to recreate an index for a desc table (such as column-store cudesc table), an exclusive lock is added to block related read/write operations on the table.

Procedure

Assume the ordinary index areaS_idx exists in the area_id column of the imported table areaS. Use either of the following two methods to recreate an index:

• Run the DROP INDEX statement to delete the index and run the CREATE INDEX statement to create an index.

  1. Delete the index.

     mogdb=# DROP INDEX areaS_idx;
     DROP INDEX

  2. Create an index

     mogdb=# CREATE INDEX areaS_idx ON areaS (area_id);
     CREATE INDEX

• Run REINDEX to recreate an index.

  • Run REINDEX TABLE to recreate an index.

    mogdb=# REINDEX TABLE areaS;
    REINDEX

  • Run REINDEX INTERNAL TABLE to recreate an index for a desc table (such as column-store cudesc table).

    mogdb=# REINDEX INTERNAL TABLE areaS;
    REINDEX

NOTE: Before you recreate an index, you can increase the values of maintenance_work_mem and psort_work_mem to accelerate the index recreation.