Tomasz Grabiec 8fa704972f loading_cache: Make invalidation take immediate effect ...

There are two issues with current implementation of remove/remove_if:

  1) If it happens concurrently with get_ptr(), the latter may still
  populate the cache using value obtained from before remove() was
  called. remove() is used to invalidate caches, e.g. the prepared
  statements cache, and the expected semantic is that values
  calculated from before remove() should not be present in the cache
  after invalidation.

  2) As long as there is any active pointer to the cached value
  (obtained by get_ptr()), the old value from before remove() will be
  still accessible and returned by get_ptr(). This can make remove()
  have no effect indefinitely if there is persistent use of the cache.

One of the user-perceived effects of this bug is that some prepared
statements may not get invalidated after a schema change and still use
the old schema (until next invalidation). If the schema change was
modifying UDT, this can cause statement execution failures. CQL
coordinator will try to interpret bound values using old set of
fields. If the driver uses the new schema, the coordinaotr will fail
to process the value with the following exception:

  User Defined Type value contained too many fields (expected 5, got 6)

The patch fixes the problem by making remove()/remove_if() erase old
entries from _loading_values immediately.

The predicate-based remove_if() variant has to also invalidate values
which are concurrently loading to be safe. The predicate cannot be
avaluated on values which are not ready. This may invalidate some
values unnecessarily, but I think it's fine.

Fixes #10117

Message-Id: <20220309135902.261734-1-tgrabiec@scylladb.com>

2022-03-09 16:13:07 +02:00

13 KiB

Raw Blame History

View Raw