Identify and repair issues with PostgreSQL® indexes with
PostgreSQL® indexes can become corrupted due to a variety of reasons including software bugs, hardware failures or unexpected duplicated data.
REINDEX allows you to rebuild the index in such situations.
Rebuild non-unique indexes¶
You can rebuild corrupted indexes that do not have
UNIQUE in their definition using the following command, that creates a new index replacing the old one:
REINDEX INDEX <index-name>;
Re-indexing applies locks to the table and may interfere with normal use of the database. In some cases, it can be useful to manually build a second index concurrently alongside the old index and then remove the old index:
CREATE INDEX CONCURRENTLY foo_index_new ON table_a (...); DROP INDEX CONCURRENTLY foo_index_old; ALTER INDEX foo_index_new RENAME TO foo_index;
You can run the
REINDEX command for:
all indexes of a table (
all indexes in the entire database (
For more information on the
REINDEX command, see the PostgreSQL documentation page.
Rebuild unique indexes¶
UNIQUE index works on top of one or more columns whose combination is unique in a table. In situations when the index is corrupted or disabled and duplicated physical rows appear in the table, breaking the uniqueness constraint of the index, then index rebuilding with
REINDEX will fail. To solve such a problem, you’ll first need to remove the duplicated rows from the table before attempting to rebuild the index.
Identify conflicting duplicated rows¶
To identify conflicting duplicate rows, you need to run a query that counts the number of rows for each combination of columns included in the index definition.
For example, the following
route table has a
unique_route_index index defining unique rows based on the combination of the
CREATE TABLE route( source TEXT, destination TEXT, description TEXT ); CREATE UNIQUE INDEX unique_route_index ON route (source, destination);
unique_route_index is corrupted, you can find duplicated rows in the
route table by issuing the following query:
SELECT source, destination, count FROM (SELECT source, destination, COUNT(*) AS count FROM route GROUP BY source, destination) AS foo WHERE count > 1;
The above query groups the data by the same
destination fields defined in the index, and filters any entries with more than one occurrence.
The resulting rows identify the problematic entries, which must be resolved manually by deleting or merging the entries until no duplicates exist.
Once duplicated entries are removed, you can use the
REINDEX command to rebuild the index.