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(Added brief note on POSTGRES_HOT_STANDBY_DELAY.)
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== Monitoring ==
=== POSTGRES_HOT_STANDBY_DELAY ===
This alert indicates that a replica has fallen behind the master database in replication. This is not immediately a cause for panic, as a host can recover assuming it is not left out of replication for long. However, the postgres logs should be examined and connectivity between individual replicas and the master should also be checked.
If many or all hosts in the maps cluster are issuing this alert, it could be the case that the OSM dataset is being refreshed - during this operation it is likely that hosts will fall behind as large numbers of changes happen on the master during import. Check the cluster masters for import processes - generally this is a passing problem and will self-resolve over time. [[Service restarts#maps|Avoid restarting postgres]] hosts while the <code>osm-replicate</code> or <code>osmosis</code> processes are running on the master. 
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Revision as of 13:17, 7 January 2021

Monitoring

POSTGRES_HOT_STANDBY_DELAY

This alert indicates that a replica has fallen behind the master database in replication. This is not immediately a cause for panic, as a host can recover assuming it is not left out of replication for long. However, the postgres logs should be examined and connectivity between individual replicas and the master should also be checked.

If many or all hosts in the maps cluster are issuing this alert, it could be the case that the OSM dataset is being refreshed - during this operation it is likely that hosts will fall behind as large numbers of changes happen on the master during import. Check the cluster masters for import processes - generally this is a passing problem and will self-resolve over time. Avoid restarting postgres hosts while the osm-replicate or osmosis processes are running on the master.

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