Skip loading of head revision on write calls #1176
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area/api v1
| func MustRevisionFromContext(ctx context.Context) (datastore.Revision, *v1.ZedToken) { | ||
| // RevisionFromContextOrError reads the selected revision out of a context.Context, computes a zedtoken | ||
| // from it, and returns an error if it has not been set on the context. | ||
| func RevisionFromContextOrError(ctx context.Context) (datastore.Revision, *v1.ZedToken, error) { |
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I don't think this name needs the OrError as the common idiom in Go already -- just drop the Must so that it's RevisionFromContext
| } | ||
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| return rev, zedtoken.MustNewFromRevision(rev) | ||
| // RevisionFromContextOrError reads the selected revision out of a context.Context, computes a zedtoken |
internal/services/v1/schema.go
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| @@ -46,15 +45,21 @@ type schemaServer struct { | |||
| } | |||
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| func (ss *schemaServer) ReadSchema(ctx context.Context, in *v1.ReadSchemaRequest) (*v1.ReadSchemaResponse, error) { | |||
| readRevision, _ := consistency.MustRevisionFromContext(ctx) | |||
| ds := datastoremw.MustFromContext(ctx).SnapshotReader(readRevision) | |||
| // Schema is already read from the head revision. | |||
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hrm, this comment assumes the reader has context about the previous implementation. I'd clarify that this method does not have consistency specified and thus we need to explicitly get head revision as it won't be available in the context.
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Sorry; should have said "always". I've fixed
| return nil, rewriteError(ctx, err) | ||
| } | ||
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| reader := ds.SnapshotReader(headRevision) |
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a potential optimization would be to have a method like HeadReader which executes the first query and returning the revision, and uses that revision for any potential subsequent queries. That way we avoid one roundtrip
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Not sure how it avoids a roundtrip; SnapshotReader(...) should not be making a DB call until its actually used
These APIs do not use consistency blocks, so there is no need to load the head revision outside of their transactions
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Rebased and updated |
These APIs do not use consistency blocks, so there is no need to load the head revision outside of their transactions