In PostgreSQL, the lock behavior during an INSERT operation depends on the type of table that the operation is performed on.
For a normal table, an INSERT lock is typically acquired on the table, which prevents concurrent transactions from accessing the table while the INSERT is in progress. The lock will be released when the transaction is committed or rolled back.
For a concurrently-accessible table (such as a table with the “WITH (INSERT_concurrently)” option), the INSERT operation uses a row-level lock instead of a table-level lock. This allows concurrent transactions to access other rows in the table while the INSERT operation is in progress, but it also means that the INSERT operation must perform additional checks to ensure data integrity.
In both cases, the lock behavior can be influenced by various configuration options, such as the lock timeout or the lock management strategy, so it’s important to carefully consider these settings when optimizing the performance of INSERT operations in PostgreSQL.
How to configure lock timeout in PostgreSQL 16?
In PostgreSQL, lock timeout can be configured in the configuration file, postgresql.conf. You can add or modify the lock_timeout setting to set the lock timeout in milliseconds. For example:
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lock_timeout = 5000 |
This sets the lock timeout to 5000 milliseconds, or 5 seconds.
It’s important to note that this setting only affects the WAIT timeout for lock requests. If a lock request times out, the transaction will be rolled back with an error.
Additionally, you can also set the lock timeout at the session level by using the SET statement:
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SET lock_timeout = 5000; |
This will only affect the current session, and will not persist across restarts.
To monitor locks in PostgreSQL, you can use the pg_locks view in the pg_catalog schema. The following SQL script will return the lock type, database, relation, page, tuple, transaction ID, and process ID for each lock:
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SELECT locktype, database, relation, page, tuple, transactionid, pid FROM pg_catalog.pg_locks; |
To monitor the duration of locks, you can use the pg_stat_activity view in the pg_catalog schema. The following SQL script will return the lock duration and source query for each lock:
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SELECT age(now(), xact_start) AS lock_duration, query FROM pg_catalog.pg_stat_activity WHERE state = 'idle in transaction'; |
Note: The age function is used to calculate the difference between the current time and the start time of the transaction. The state column in pg_stat_activity is used to filter for transactions that are idle in the transaction, which indicates that a lock is being held.
