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Update replication stream docs to better describe role of POSITION #16560

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erikjohnston opened this issue Oct 27, 2023 · 1 comment
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Update replication stream docs to better describe role of POSITION #16560

erikjohnston opened this issue Oct 27, 2023 · 1 comment
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A-Docs things relating to the documentation A-Workers Problems related to running Synapse in Worker Mode (or replication) T-Task Refactoring, removal, replacement, enabling or disabling functionality, other engineering tasks.

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@erikjohnston
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c.f. #16555 (comment)
@erikjohnston erikjohnston mentioned this issue Oct 27, 2023
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@DMRobertson
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DMRobertson commented Oct 27, 2023 •
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Examples are the key here, I think.

An incoming POSITION sends two numbers prev < next. (I assume that prev = next or next < prev are invalid?) The worker processing the POSITION has its own position "current". There are then five cases to illustrate:

  • current < prev < next
  • current = prev < next
  • prev < current < next
  • prev < current = next
  • prev < next < current

(The invariant we apparently want is prev <= current <= next, i.e. the middle three bullets.)

@DMRobertson DMRobertson added A-Docs things relating to the documentation A-Workers Problems related to running Synapse in Worker Mode (or replication) T-Task Refactoring, removal, replacement, enabling or disabling functionality, other engineering tasks. labels Oct 27, 2023
@matrixbot matrixbot mentioned this issue Dec 22, 2023
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