After upgrading to mysql 8.0.25 from 5.7.31, xtrabackup --prepare consumes high amounts of memory for databases with many tables.
--use-memory does not make any difference.
Number of tables is around 1-2 millions.
For example with
--use-memory 256M argument for a server with 400 000 tables (each in a separate file) xtrabackup consumes around 8Gi of memory.
When number of tables is close to 1 000 000, it consumes more than 20Gi of memory.
Is it expected? With mysql 5.7
--use-memory argument worked fine, and memory consumptions was close it.