Hi, I've created the new thread for the changing AV launcher scheduling. The problem of AV launcher scheduling is described on [1] but I summarize it here.
If there is even one database that is at risk of wraparound, currently AV launcher selects the database having the oldest datfrozenxid until all tables in that database have been vacuumed. This leads that tables on other database can bloat and not be frozen because other database are not selected by AV launcher. It makes things worse if the database has a large table that takes a long time to be vacuumed. Attached patch changes the AV launcher scheduling algorithm based on the proposed idea by Robert so that it selects a database first that has the oldest table when the database is at risk of wraparound. For detail of the algorithm please refer to [2]. In this algorithm, the running AV workers advertise the next datfrozenxid on the shared memory that we will have. That way, AV launcher can select a database that has the oldest table in the database cluster. However, this algorithm doesn't support the case where the age of next datfrozenxid gets greater than autovacum_vacuum_max_age. This case can happen if users set autovacvuum_vacuum_max_age to small value and vacuuming the whole database takes a long time. But since it's not a common case and it doesn't degrade than current behavior even if this happened, I think it's not a big problem. Feedback is very welcome. [1] https://www.postgresql.org/message-id/0A3221C70F24FB45833433255569204D1F8A4DC6%40G01JPEXMBYT05 [2] https://www.postgresql.org/message-id/CA%2BTgmobT3m%3D%2BdU5HF3VGVqiZ2O%2Bv6P5wN1Gj%2BPrq%2Bhj7dAm9AQ%40mail.gmail.com Regards, -- Masahiko Sawada NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center
autovacuum_scheduling.patch
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