"This series contains some fixes and a unit test for the logic responsible
for locking counter cells."
* 'pdziepak/cell-locking-fixes/v1' of github.com:cloudius-systems/seastar-dev:
tests: add test for counter cell locker
cell_locking: fix schema upgrades
cell_locker: make locker non-movable
cell_locking: allow to be included by anyone
(cherry picked from commit b8c4b35b57)
The comparator constructor took schema by value instead of const l-ref
and, consequently, later tried to access object that has been destroyed
long time ago.
Message-Id: <20170202135853.8190-1-pdziepak@scylladb.com>
(cherry picked from commit 37b0c71f1d)
The leader receives counter update in a form of deltas which need to be
transformed to counter shards. In order to do that the node needs to
read its current state of the modified counter cells. Since this is
essentially a read-modify-write opertation an appropriate locking
mechanism is needed.
Counter cell locker introduced in this patch uses a hashtable of
partition entry each containing a hashtable of cell entries. Inside a
cell entry there is a semaphore used for synchronization. Once no longer
needed cell entries and partition entries are removed.
In order to avoid deadlocks cell entries are always locked in the same
order which is the lexicographical order of (clustering key, column id)
pairs. Note that schema changes are not a difficulty since they do not
make it possible to change ordering of such pairs.
