Обсуждение: pgsql: Fix and improve SnapshotType comments.

Fix and improve SnapshotType comments.

The comment for SNAPSHOT_SELF was unfortunately explaining
SNAPSHOT_DIRTY, as reported by Sergei. Also expand a few comments, and
include a few more comments from heapam_visibility.c, so they're in an
AM independent place.

Reported-By: Sergei Kornilov
Author: Andres Freund
Discussion: https://postgr.es/m/9152241558192351@sas1-d856b3d759c7.qloud-c.yandex.net

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/78d6a9cbd3438969ac87b9f1aaf0f07226636ed7

Modified Files
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src/include/utils/snapshot.h | 29 ++++++++++++++++++++++++-----
1 file changed, 24 insertions(+), 5 deletions(-)