REP-6766 Compare documents using a batch cursor #148
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FGasper
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tdq45gj
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Oct 31, 2025
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I've left some non-blocking questions. Thanks!
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| if err == nil { | ||
| c.SetSession(mongo.SessionFromContext(ctx)) | ||
| } |
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Is there a reason why SetSession is exported and called in the verifier code? Can we set the session in the cursor constructor?
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I had it that way for a bit, but then we’d need 2 constructors (one with a session & the other without).
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I’m starting to wonder, though, if it should always require a session. The driver does some funny-business under the hood to ensure that cursors always send the same LSID as the initial request.
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This alters document comparison to use a batch cursor instead of the Go driver’s cursor. The advantage here is that, instead of creating giant slices of documents (which are copied from the driver), we’ll read the raw documents directly from the server response buffer. This minimizes GC pressure.
Pprof analysis shows that before this change, slices.Clone() allocated more heap than any other functions. With this change, those allocations are gone.
PR #153 will make the change stream use the same batch cursor.