PostgresDB Slow Queries
Queries taking longer than expected or performance degradation over time, particularly for complex queries or joins.
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What is
PostgresDB Slow Queries
?
- Identify Slow Queries:Use the
pg_stat_statementsextension to find slow queries. If not enabled, enable it by addingpg_stat_statementstoshared_preload_librariesin yourpostgresql.conf, then restart your PostgreSQL server and run: CREATE EXTENSION pg_stat_statements;- Afterward, to find slow queries, run:
SELECT query, calls, total_time, rows, 100.0 * shared_blks_hit / nullif(shared_blks_hit + shared_blks_read, 0) AS hit_percent, avg_time, max_time, min_time
FROM pg_stat_statements
ORDER BY total_time DESC
LIMIT 10;- Analyze the Execution Plan:For any identified slow query, analyze its execution plan using
EXPLAIN ANALYZE. ReplaceYOUR_QUERYwith the slow query: EXPLAIN ANALYZE YOUR_QUERY;- Indexing:
- If the execution plan shows sequential scans on large tables or slow index scans, consider adding or optimizing indexes. Use:
CREATE INDEX ON table_name (column_name);- To identify missing indexes, you can also use:
SELECT * FROM pg_stat_user_indexes JOIN pg_index USING(indexrelid) WHERE idx_scan < 50 AND indisunique IS FALSE;
- Vacuum and Analyze Tables:
- To reclaim storage and update stats, run:
VACUUM VERBOSE ANALYZE table_name;- For routine maintenance, ensure autovacuum is enabled.
- Check Locks:Identify if the slow queries are due to locking issues:
SELECT pid, age(clock_timestamp(), query_start), usename, query
FROM pg_stat_activity
WHERE state = 'active' AND query NOT LIKE '%pg_stat_activity%'
ORDER BY query_start desc;- Connection Pooling:If the slow queries are related to opening and closing many connections, consider implementing connection pooling outside of PostgreSQL, using PgBouncer or a similar tool.
- Adjust Configuration Settings:Review and adjust configuration settings in
postgresql.confrelated to performance, such aswork_mem,maintenance_work_mem,shared_buffers, andeffective_cache_sizebased on your server's resources and workload. - Query Refactoring:For complex queries, consider refactoring by:
- Breaking down the query into smaller parts.
- Avoiding sub-selects in WHERE clause.
- Using JOINs instead of IN/NOT IN with subqueries.
- Using WITH queries (Common Table Expressions) to simplify complex JOINs.
- Use Parallel Query Execution:Ensure that your PostgreSQL version supports parallel query execution and that it is enabled for your server. This can be beneficial for executing large queries but depends on the PostgreSQL version and the specific query.
Attached error:
PostgresDB Slow Queries
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