Add UpdatesOnly query option to fetch data for only changed keys #22108
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tanmayghai18
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As mentioned long ago (and roughly outlined) in hashicorp#2791, a limitation on blocking queries is that all K/V entries matching that prefix are returned, even though only 1 key may have changed. This diff adds a new `UpdatesOnly` option, that when set, introduces server-side filtering to remove all keys/entries (from a `Keys()` or `List()` query) that have an old `ModifyIndex`. It uses `MinQueryIndex` as the threshold here, which follows the effective serialization/deserialization chain: `WaitIndex` --> `index` --> `MinQueryIndex`. - `WaitIndex` being the client-side parameter, determining the index the "client" waits for on a blocking query - `index` being the serialized HTTP query parameter representing the `WaitIndex` - `MinQueryIndex` being the server-side struct (deserialized result of `index`) While we (potentially?) wait for the streaming backend: https://developer.hashicorp.com/consul/api-docs/features/blocking#streaming-backend to be implemented for KV endpoints, this can be a good stop-gap solution to enable in-memory, incremental scans or queries over a prefix.
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tanmayghai18
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Jan 28, 2025
| reply.QueryMeta.ResultsFilteredByACLs = total != len(ent) | ||
| total := len(entries) | ||
| entries = FilterDirEnt(authz, entries) | ||
| reply.QueryMeta.ResultsFilteredByACLs = total != len(entries) |
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open q: similar to how we hydrate ResultsFilteredByACLs in the QueryMeta introduced by #11569, does it make sense to do the same thing here for filtering by query index?
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Description
As mentioned long ago (and roughly outlined) in #2791, a limitation on blocking queries is that all K/V entries matching that prefix are returned, even though only 1 key may have changed. This diff adds a new
UpdatesOnlyoption, that when set, introduces server-side filtering to remove all keys/entries (from aKeys()orList()query) that have an oldModifyIndex.It uses
MinQueryIndexas the threshold here, which follows the effective serialization/deserialization chain:WaitIndex-->index-->MinQueryIndex.WaitIndexbeing the client-side parameter, determining the index the "client" waits for on a blocking queryindexbeing the serialized HTTP query parameter representing theWaitIndexMinQueryIndexbeing the server-side struct (deserialized result ofindex)While we (potentially?) wait for the streaming backend: https://developer.hashicorp.com/consul/api-docs/features/blocking#streaming-backend to be implemented for KV endpoints, this can be a good stop-gap solution to enable in-memory, incremental scans or queries over a prefix.
Testing & Reproduction steps
minQueryIndexpassed down the state layer to be 0 (no filtering)state/kvs_test.goto illustrate the filtering based onModifyIndexLinks
Original GH issue: #2791
PR Checklist