Does Coherence optimize request routing to stay within racks where possible? about coherence HOT 7 CLOSED

Is this what you mean:

https://coherence.community/22.06-SNAPSHOT/docs/#/docs/core/09_backup

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@javafanboy just as a follow up for clarification:

• if neither scheduled-backups nor async-backup are set, then mutations will wait for backup requests to be performed before responding, regardless of number of backups. This can lead to slower response times on put/putAlls. async-backup still waits for backup requests to be sent before returning to the client. If your application is read-heavy then you won't be affected too much by this. scheduled-backups does not wait, but can lead to data loss in the time that backups are not done yet.

• with "read-locator" there is a possibility to enter "dirty reads" situations, but I think you are already aware of that.

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Thanks for the clarification!

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Basically, yes, you need to have enough RAM to allow for the amount of failure you want to support. Assuming you have configured Coherence so it can be site safe (setting the coherence.site property) or rack safe (setting the coherence.rack property) then failure of a rack, say will mean the data is recovered from backups in the remaining racks, then new backups also allocated in the remaining racks. The only time backups will not be allocated is when you only have one JVM in the cluster. If Coherence did not do this, then when you lost a rack for example, then the data in the caches would be endangered until new members came up on a new rack, any other JVM departure during this time would cause data loss. We do have quorum configurations in Coherence that controls various behaviours, I'm not sure off the top of my head whether backups is one of them. I'll ask, or someone who knows can answer.

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Also, I believe Coherence will not try to totally unbalance a cluster. For example say you had five cluster members on each of
two racks. The you lost four members on one rack leaving only one member on that rack and five on the other rack. I'm pretty sure Coherence would not try to allocate all the backups into the one renaming member on the rack.

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