A115: disable priority LB child policy retention cache

A56-update-remove-priority-lb-child-policy-cache.md

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+A56: disable Priority LB policy child policy retention cache
+----
+* Author(s): @apolcyn
+* Approvers: @markdroth, @ejona86, @dfawley, @easwars
+* Status: {Draft}
+* Implemented in: C-core, Java, Go, Node
+* Last updated: 2026-03-17
+* Discussion at: <google group thread> (filled after thread exists)
+
+## Abstract
+
+[A56](https://github.com/grpc/proposal/blob/master/A56-priority-lb-policy.md) describes
+a [caching mechanism](https://github.com/grpc/proposal/blob/master/A56-priority-lb-policy.md#child-lifetime-management) whereby priority LB child policies are kept around for an additional 15 minutes
+before being fully torn down.
+
+This proposal removes that cache.
+
+## Background
+
+The priority LB child policy retention cache consumes excessive memory under the
+right circumstances (depending on the rate and pattern of locality updates).
+
+This is especially the case when a locality is flapping between failover and primary
+priorities. For example, notice how priority LB child names increase in the following
+sequence of locality updates. On each child name update, previous policies are added
+to the retention cache.
+
+```
+[[AA,BB],[CC, DD]] => [priority-0-0 priority-0-1]
+[[AA, BB, CC], [DD]] => [priority-0-1 priority-0-2]
+[[AA, BB], [CC, DD]] => [priority-0-1 priority-0-2]
+[[AA, BB, CC], [DD]] => [priority-0-2 priority-0-3]
+[[AA, BB], [CC, DD]] => [priority-0-2 priority-0-3]
+[[AA, BB, CC], [DD]] => [priority-0-3 priority-0-4]
+```
+
+Additionally, priority LB child names are generated with strictly increasing numbers
+(once a priority LB child name is unconfigured, it will never be configured again). As such,
+the cache is not providing us value.
+
+## Proposal
+
+Priority LB should disable the child policy retention cache.
+
+### Temporary environment variable protection
+
+N/A
+
+## Rationale
+
+N/A
+
+## Implementation
+
+N/A
+
+## Open issues (if applicable)
+
+N/A