This PR fixes a lock issue that happens while executing
`ALTER LIVE VIEW` query with the `REFRESH` command that
results in a exception. The problem is that lock is currently
being acquired in `InterpreterALterQuery.cpp`
in the `InterpreterAlterQuery::execute()` method and lock
is again being reacquired in `StorageLiveView.cpp` in the
` StorageLiveView::refresh` method. This removes that extra
lock.
Before fix:
```sql
--create table
CREATE TABLE test0 (
c0 UInt64
) ENGINE = MergeTree() PARTITION BY c0 ORDER BY c0;
-- enable experimental_live_view
:) SET allow_experimental_live_view=1
-- create live view;
:) CREATE LIVE VIEW live1 AS SELECT * FROM table0;
-- alter live view results in exception
:) ALTER LIVE VIEW live1 REFRESH;
...
...
Received exception from server (version 20.8.1):
Code: 49. DB::Exception: Received from localhost:9000. DB::Exception: RWLockImpl::getLock(): RWLock is already locked in exclusive mode.
```
After fix:
```sql
:) ALTER LIVE VIEW live1 REFRESH;
ALTER LIVE VIEW live1
REFRESH
Ok.
0 rows in set. Elapsed: 0.016 sec.
```
In this version of the databaseReplicated sequential persistent zk nodes
are used to order DDL queries. Db replicated ddl queries are executed
in the backgrould pool no matter whether it's proposed by the same
replica or not.
add an option to create replicated tables within replicated db without specifying zk path and replica id
add replicated sch pool
disable replication of alter queries for replicated tables in replicated dbs
snapshot prototype. amend of replicated db workflow
add prototype of integration tests for replicated db
* "lock_acquire_timeout" controls for how long a query will continue to
acquire each lock on its argument tables
* "lock_acquire_timeout_for_background_operations" is a per-table
setting for storages of *MergeTree family
