* Implementation of optimistic lock pattern

Try to insert the remote cache key and handle integrity error

* Remove transaction

Integrity error inside a transaction results in deadlock

* Remove check for existing remote cache key

Is no longer needed since integrity constrain violations are handled

* Add check for integrity constrain violation

Do not update the row if the insert statement fails
for other than an integrity constrain violation

* Handle failing inserts because of deadlocks

If the insert statement fails because of a deadlock
try to update the row

* Add utility function for returning SQL error code

Useful for debugging

* Add logging for failing expired cache key deletion

Do not shallow it completely

* Revert "Add utility function for returning SQL error code"

This reverts commit 8e0b82c79633e7d8bc350823cbbab2ac7a58c0a5.

* Better log for failing deletion of expired cache key

* Add some comments

* Remove check for existing cache key

Attempt to insert the key without checking if it's already there
and handle the error situations

* Do not propagate deadlocks created during update

Most probably somebody else is trying to insert/update
the key at the same time so it is safe enough to ignore it