catalog: add mz_replacements system relation #34332
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Once materialized views can have multiple historical storage collections associated with them, we'll need to make sure to drop all of those when dropping a materialized view. There is always only a single compute collection to drop. This commit ensures we'll do the right thing and also simplifies the item dropping code a bit in the process: Instead of keeping track of indexes/MVs/CTs to drop, we instead only track compute and storage collections to drop. Doing so allows deleting a bunch of duplicate code.
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This commit adds a feature flag to gate the creation and application of replacement materialized views. It's disabled by default and enabled in CI.
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When a replacement MV is applied, the catalog is updated by dropping the replacement and updating the target MV with a new version. This transfers both the replacement's compute and storage collection to the target MV, so they should not be dropped. The implication application logic must thus be extended to account for that.
For compute collections, it is wrong to assume that all GlobalIds associated with a catalog entry (specifically an MV catalog entry) also map to live compute collections. Instead, only the "write GlobalId" has a live compute collection. Compute collections that were previously maintaining the catalog item have likely been dropped already.
This commit adds a new `mz_replacements` builtin table, exposing the replacement MV relationship. It also adds a `replacing` column to the `SHOW MATERIALIZED VIEWS` output, fueled by the new `mz_replacements` table.
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This PR adds a new
mz_replacementsbuiltin table, exposing the replacement MV relationship. It also adds areplacingcolumn to theSHOW MATERIALIZED VIEWSoutput, fueled by the newmz_replacementstable.Motivation
Tips for reviewer
Checklist
$T ⇔ Proto$Tmapping (possibly in a backwards-incompatible way), then it is tagged with aT-protolabel.