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When a busy PostgreSQL table needs an index, a structure that helps PostgreSQL find rows, use CREATE INDEX CONCURRENTLY to let inserts, updates, and deletes continue while PostgreSQL…
Read articleWhen you change the schema of a busy PostgreSQL database, each data definition language (DDL) command determines what PostgreSQL does and which other sessions wait. DDL commands are…
Read articleIn PostgreSQL, a query sees an inserted row based on the transaction’s isolation level and when the query starts. At the default Read Committed level, PostgreSQL gives each…
Read articleIn PostgreSQL, READ COMMITTED is the default setting that controls which committed changes a transaction can see. It gives each SQL statement a fresh snapshot: a view of…
Read articleIn PostgreSQL, a transaction using REPEATABLE READ sees one stable view of committed data across its queries. If another session commits a change while the transaction is open,…
Read articleWhen code in a PostgreSQL web application runs SELECT ... FOR UPDATE, PostgreSQL locks the rows the query selects. Another transaction cannot update or delete those rows until…
Read articlePostgreSQL defaults to READ COMMITTED. A transaction groups statements that should succeed or fail together. Under READ COMMITTED, each SQL statement sees committed data as other requests change…
Read articleWhen PostgreSQL runs a query, its planner builds an execution plan by comparing indexes that support the query’s conditions. It uses data statistics and estimated costs to compare…
Read articleWhen a production PostgreSQL table needs a new value for existing rows, update a limited set of rows at a time and commit each batch. This update of…
Read articleWhen you add a composite index to a MySQL table, the order of its columns determines which queries can use it efficiently. A composite index is one index…
Read articleOn a PostgreSQL table serving a live web application, a regular index build can cause an outage because it holds a lock while PostgreSQL scans the table and…
Read articleWhen a MySQL database responds slowly, the SQL statements taking the most time are a useful place to investigate. The slow query log records statements that exceed a…
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