[WAGED Tag Isolation 8/16] Attribute a capacity deficit to the cliques that caused it - #288
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The cluster wide capacity check that runs before any placement is a tag blind sum, so one wildly oversubscribed clique can drag a dimension negative while every other clique still fits comfortably on its own nodes. Throwing there would freeze the whole cluster, which is what this mode exists to prevent. Walk the attribution blocks instead, set aside the ones whose own replicas cannot fit on their own nodes, and re-evaluate the deficit on what is left. The blocks set aside are carried over like any other failed group. A deficit that survives that, or a cluster that is one single block, still throws exactly as before. Only reachable on a path where the default mode has already decided to throw, so nothing changes for a cluster that fits.
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Description
The cluster wide capacity check that runs before any placement is a tag blind sum, so one wildly oversubscribed clique can drag a dimension negative while every other clique still fits comfortably on its own nodes. Throwing there would freeze the whole cluster, which is what this mode exists to prevent.
Walk the attribution blocks instead, set aside the ones whose own replicas cannot fit on their own nodes, and re-evaluate the deficit on what is left. A deficit that survives that, or a cluster that is one single block, still throws exactly as before.
This completes the production code for the feature.
Stacked PR 8 of 16 of the WAGED instance tag isolation stack.
lzd/waged-iso-07-hookswaged-tag-based-isolation, which merges intodevat the endTests
Existing WAGED suites stay green. The attribution tests arrive in lzd/waged-iso-16-tests-capacity.
Changes that Break Backward Compatibility
None. The new cluster config flag defaults to false, and with it off every code path added here behaves exactly as it does today.
Documentation
The design doc lands in
lzd/waged-iso-13-docasdocs/design/002-waged-instance-tag-isolation.md.Code Quality
Formatted with helix-style.xml.