But suppose you want to do a snapshot soon two rules

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Unformatted text preview: soon? Two rules: Marker-Sending Rule for a Process p. For each channel c, incident on, and directed away from p: p sends one marker along c after p records its state and before p sends further messages along c. Marker-Receiving Rule for a Process q. On receiving a marker along a channel c: if q has not recorded its state then begin q records its state; q records the state c as the empty sequence end else q records the state of c as the sequence of messages received along c after q’s state was recorded and before q received the marker along c. E.g., for distributed garbage collection – any data structures that can’t be reached in the consistent snapshot, are safe to reclaim. Data that is live in the consistent snapshot might be dead by the time we complete the snapshot! We’re only guaranteed that data that was dead at the time the snapshot STARTED, will be seen as dead. Data that became dead during the snapshot might be seen as live or dead. Data that is live at the end, will be seen as live (or possibly, newly created). But its ok to miss newly dead data, we’ll take another snapshot later on, to collect new garbage....
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