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How does reindex help to improve PostgreSQL performance?
REINDEX provides a recovery method. An index has become “bloated”, that is it contains many empty or nearly-empty pages. This can occur with B-tree indexes in PostgreSQL under certain uncommon access patterns. REINDEX provides a way to reduce the space consumption of the index by writing a new version of the index without the dead pages.
What happens when an index is corrupted in PostgreSQL?
An index has become corrupted, and no longer contains valid data. Although in theory this should never happen, in practice indexes can become corrupted due to software bugs or hardware failures. REINDEX provides a recovery method.
How does the DROP INDEX work in PostgreSQL?
In contrast, DROP INDEX momentarily takes an exclusive lock on the parent table, blocking both writes and reads. The subsequent CREATE INDEX locks out writes but not reads; since the index is not there, no read will attempt to use it, meaning that there will be no blocking but reads might be forced into expensive sequential scans.
How to recover from a PostgreSQL server crash?
To recover safely, the server must be started with the -P option, which prevents it from using indexes for system catalog lookups. One way to do this is to shut down the server and start a single-user PostgreSQL server with the -P option included on its command line.
How to reconstruct an index in PostgreSQL?
To reconstruct one or more indexes, we generally use the PostgreSQL REINDEX statement. Sometimes due to software problems or bugs or some hardware failures, the indexes got corrupted; in such cases, we can use this statement to recover the index. We can recreate the index for TABLE, SCHEMA, DATABASE, or SYSTEM DATABASE and recreate the INDEX.
When to use reindex on a user table?
Prints a progress report as each index is reindexed. If you suspect corruption of an index on a user table, you can simply rebuild that index, or all indexes on the table, using REINDEX INDEX or REINDEX TABLE. Things are more difficult if you need to recover from corruption of an index on a system table.
How to check the index size in PostgreSQL?
Here’s a sample query to pull the number of rows, indexes, and some info about those indexes for each table. Table & index sizes along which indexes are being scanned and how many tuples are fetched. See Disk Usage for another view that includes both table and index sizes.
Can You reindex a toast table in PostgreSQL?
Recreate all indexes of the specified table. If the table has a secondary “TOAST” table, that is reindexed as well. Recreate all indexes within the current database. Indexes on shared system catalogs are also processed. This form of REINDEX cannot be executed inside a transaction block.