Today, while studying your proposal and related material, I noticed
that in both the approaches DTM and tsDTM, you are talking about
committing a transaction and acquiring the snapshot consistently, but
not touched upon the how the locks will be managed across nodes and
how deadlock detection across nodes will work. This will also be one
of the crucial points in selecting one of the approaches.
Lock manager is one of the tasks we are currently working on. There are still a lot of open questions: 1. Should distributed lock manager (DLM) do something else except detection of distributed deadlock? 2. Should DLM be part of XTM API or it should be separate API? 3. Should DLM be implemented by separate process or should it be part of arbiter (dtmd). 4. How to globally identify resource owners (0transactions) in global lock graph. In case of DTM we have global (shared) XIDs, and in tsDTM - global transactions IDs, assigned by application (which is not so clear how to retrieve). In other cases we may need to have local->global transaction id mapping, so looks like DLM should be part of DTM...
Yes, we need a Distributed Lock Manager, but I think its a separate thing from the DTM.
(I'm loath to use the phase DLM, which was used within Oracle Parallel server for a buffer lock manager, which is not what is being discussed).
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Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
