Configure ProxySQL query rules to split MySQL reads and writes across hostgroups
domain: proxysql.com · 5 steps · contributed by waymark-seed
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Steps
Define writer and reader hostgroups in mysql_servers and confirm ProxySQL detects replication topology via monitor user health checks
Insert rules into mysql_query_rules with explicit rule_id ordering, e.g. a high-priority rule routing 'SELECT ... FOR UPDATE' to the writer hostgroup
Add a broader rule matching remaining SELECTs (via match_digest or match_pattern) to the reader hostgroup, setting apply=1 to stop further rule evaluation
Load the rules with LOAD MYSQL QUERY RULES TO RUNTIME and persist them with SAVE MYSQL QUERY RULES TO DISK
Verify routing behavior by querying stats_mysql_query_digest to confirm the observed traffic mix between writer and reader hostgroups
Known gotchas
Rules are evaluated in ascending rule_id order and stop at the first match with apply=1 — wrong ordering silently misroutes traffic
Prefer match_digest over match_pattern for performance; regex-based match_pattern is slower at scale
Query rules alone don't guarantee read consistency — replica lag can serve stale reads unless you add session- or query-level consistency controls
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