The log message for commit a9af1ac5ae
explained:
In some older BIND 9 branches, the extra queuing overhead eliminated by
this change could be remotely exploited to cause excessive memory use.
Due to architectural shift, this branch is not vulnerable to that issue,
but applying the fix to the latter is nevertheless deemed prudent for
consistency and to make the code future-proof.
However, it turned out that having a single queue for the nodes to be
pruned increased lock contention to a level where cleaning up nodes from
the RBTDB took too long, causing the amount of memory used by the cache
to grow indefinitely over time.
This commit reverts the change to the pruning mechanism introduced by
commit a9af1ac5ae as BIND branches newer
than 9.16 were not affected by the excessive event queueing overhead
issue mentioned in the log message for the above commit.
(cherry picked from commit eed17611d8)
4b32456705