𝗗𝗔𝗧𝗔𝗕𝗔𝗦𝗘 𝗤𝗨𝗘𝗥𝗬 𝗢𝗣𝗧𝗜𝗠𝗜𝗭𝗔𝗧𝗜𝗢𝗡

𝗗𝗔𝗧𝗔𝗕𝗔𝗦𝗘 𝗤𝗨𝗘𝗥𝗬 𝗢𝗣𝗧𝗜𝗠𝗜𝗭𝗔𝗧𝗜𝗢𝗡

Slow queries kill app speed. One bad query slows things down for everyone.

Find your slow queries first. Use these tools:

• PostgreSQL: pg_stat_statements
• MySQL: slow query log
• SQL Server: sys.dm_exec_query_stats

Use EXPLAIN ANALYZE to see how your database works.

• Look for sequential scans. These mean you need indexes.
• Look for nested loop joins. These need better join plans.

Add the right indexes.

• Index columns in WHERE, JOIN, and ORDER BY.
• Use composite indexes for multiple columns.
• Put equality filters first. Put range filters last.

Use covering indexes. These contain all columns for a query. The database reads only the index. This is an index-only scan. It is faster.

Rewrite your queries.

• Use UNION ALL instead of OR.
• Use EXISTS instead of IN.
• Stop using functions in WHERE clauses.

Partition large tables. Use dates or regions. The database scans fewer rows. This also helps backups.

Test with real data volumes. Dev data is too small. Use anonymous production data. Measure results before and after deployment.

Source: https://dev.to/therizwansaleem/database-query-optimization-reading-query-plans-and-fixing-slow-queries-5pk