From 818d1c3b068c6705611256cfc3eb1f10bdc0b684 Mon Sep 17 00:00:00 2001 From: Melanie Plageman Date: Fri, 1 Nov 2024 18:25:05 -0400 Subject: [PATCH v1 8/9] WIP: Add more general summary to vacuumlazy.c Currently the summary at the top of vacuumlazy.c provides some specific details related to the new dead TID storage in 17. I plan to add a summary and maybe some sub-sections to contextualize it. --- src/backend/access/heap/vacuumlazy.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c index 7ce69953ba0..15a04c6b10b 100644 --- a/src/backend/access/heap/vacuumlazy.c +++ b/src/backend/access/heap/vacuumlazy.c @@ -3,6 +3,17 @@ * vacuumlazy.c * Concurrent ("lazy") vacuuming. * + * Heap relations are vacuumed in three main phases. In the first phase, + * vacuum scans relation pages, pruning and freezing tuples and saving dead + * tuples' TIDs in a TID store. If that TID store fills up or vacuum finishes + * scanning the relation, it progresses to the second phase: index vacuuming. + * After index vacuuming is complete, vacuum scans the blocks of the relation + * indicated by the TIDs in the TID store and reaps the dead tuples, freeing + * that space for future tuples. Finally, vacuum may truncate the relation if + * it has emptied pages at the end. XXX: this summary needs work. + * + * Dead TID Storage: + * * The major space usage for vacuuming is storage for the dead tuple IDs that * are to be removed from indexes. We want to ensure we can vacuum even the * very largest relations with finite memory space usage. To do that, we set -- 2.34.1