Concurrency Control in PostgreSQL (cont)
Rules for a tuple to be visible to Ti :
- the
xmin (creation transaction) value must
- be committed in the log file
- have started before Ti's start time
- not be active at Ti's start time
- the
xmax (delete/replace transaction) value must
- be blank or refer to an aborted tx, or
- have started after Ti's start time, or
- have been active at SnapshotData time
For details, see: utils/time/tqual.c
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