On 3/5/23 06:49, jacktby@xxxxxxxxx wrote:
Here are the comments in src/include/utils/snapshot.h.
/*
* For normal MVCC snapshot this contains the all xact IDs that are in
* progress, unless the snapshot was taken during recovery in which case
* it's empty. For historic MVCC snapshots, the meaning is inverted, i.e.
* it contains *committed* transactions between xmin and xmax.
*
* note: all ids in xip[] satisfy xmin <= xip[i] < xmax
*/
TransactionId *xip;
I can't understand the historic MVCC snapshots? can you give me a scenario
to describe this?
From the same file:
/*
* A tuple is visible iff it follows the rules of SNAPSHOT_MVCC, but
* supports being called in timetravel context (for decoding catalog
* contents in the context of logical decoding).
*/
SNAPSHOT_HISTORIC_MVCC,
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jacktby@xxxxxxxxx
--
Adrian Klaver
adrian.klaver@xxxxxxxxxxx
