What Does Coherency Mean?
- Informally:
- “Any read must return the most recent write”
- Too strict and too difficult to implement
- Better:
- “Any write must eventually be seen by a read”
- All writes are seen in proper order (“serialization”)
- Two rules to ensure this:
- “If P writes x and P1 reads x, P’s write will be seen by P1 if the read and write are sufficiently far apart”
- Writes to a single location are serialized: seen in the same order order