Move visibility map memory ordering comments. nodeIndexonlyscan.c has long carried a detailed explanation of why it is safe for index-only scans to test a visibility map bit without locking the visibility map buffer, despite the possibility of reading a stale value. Move that explanation into visibilitymap.c.
This is preparation for an upcoming commit that will move VM checks needed by index-only scans out of the executor and into heapam. Author: Peter Geoghegan <[email protected]> Suggested-by: Andres Freund <[email protected]> Reviewed-by: Andres Freund <[email protected]> Reviewed-by: Tomas Vondra <[email protected]> Discussion: https://postgr.es/m/t6mtqbv2mbfhjni4bvwdgoecppjmxvbyfwl6utovzv76xc2672%40k3o5ryevaeqv Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/903d9d12cc0adcd9a7f92c7b35333e9e40756fbf Modified Files -------------- src/backend/access/heap/visibilitymap.c | 27 ++++++++++++++++++++++++++- src/backend/executor/nodeIndexonlyscan.c | 29 ++++------------------------- 2 files changed, 30 insertions(+), 26 deletions(-)
