- All the schema creations on the workers will now be via superuser connections
- If a shard is being repaired or a shard is replicated, we will create the
schema only in the relevant worker; and in all the other cases where a schema
creation is needed, we will block operations until we ensure the schema exists
in all the workers
It has been reported a null pointer dereference could be triggered in FreeConnParamsHashEntryFields. Likely cause is an error in GetConnParams which will leave the cached ConnParamsHashEntry in a state that would cause the null pointer dereference in a subsequent connection establishment to the same server. This has been simulated by inserting ereport(ERROR, ...) at certain places in the code.
Not only would ConnParamsHashEntry be in a state that would cause a crash, it was also leaking memory in the ConnectionContext due to the loss of pointers as they are only stored on the ConnParamsHashEntry at the end of the function.
This patch rewrites both the GetConnParams to store pointers 'durably' at every point in the code so that an error would not lose the pointer as well as FreeConnParamsHashEntryFields in a way that it can clear half initialised ConnParamsHashEntry's in a safer manner.
GRANT queries are propagated on Enterprise. If a user attempts to
create a user and run a GRANT query before creating it on workers, we
fail. This issue does not happen in community as the user needs to run
the GRANTs on the workers manually.
When `master_update_node` is called to update a node's location it waits for appropriate locks to become available. This is useful during normal operation as new operations will be blocked till after the metadata update while running operations have time to finish.
When `master_update_node` is called after a node failure it is less useful to wait for running operations to finish as they can't. The lock being held indicates an operation that once attempted to commit will fail as the machine already failed. Now the downside is the failover is postponed till the termination point of the operation. This has been observed by users to take a significant amount of time causing the rest of the system to be observed unavailable.
With this patch it is possible in such situations to invoke `master_update_node` with 2 optional arguments:
- `force` (bool defaults to `false`): When called with true the update of the metadata will be forced to proceed by terminating conflicting backends. A cancel is not enough as the backend might be in idle time (eg. an interactive session, or going back and forth between an appliaction), therefore a more intrusive solution of termination is used here.
- `lock_cooldown` (int defaults to `10000`): This is the time in milliseconds before conflicting backends are terminated. This is to allow the backends to finish cleanly before terminating them. This allows the user to set an upperbound to the expected time to complete the metadata update, eg. performing the failover.
The functionality is implemented by spawning a background worker that has the task of helping a certain backend in acquiring its locks. The backend is either terminated on successful execution of the metadata update, or once the memory context of the expression gets reset, eg. on a cancel of the statement.
Adds support for propagation of SET LOCAL commands to all workers
involved in a query. For now, SET SESSION (i.e. plain SET) is not
supported whatsoever, though this code is intended as somewhat of a
base for implementing such support in the future.
As SET LOCAL modifications are scoped to the body of a BEGIN/END xact
block, queries wishing to use SET LOCAL propagation must be within such
a block. In addition, subsequent modifications after e.g. any SAVEPOINT
or ROLLBACK statements will correspondingly push or pop variable mod-
ifications onto an internal stack such that the behavior of changed
values across the cluster will be identical to such behavior on e.g.
single-node PostgreSQL (or equivalently, what values are visible to
the end user by running SHOW on such variables on the coordinator).
If nodes enter the set of participants at some point after SET LOCAL
modifications (or SAVEPOINT, ROLLBACK, etc.) have occurred, the SET
variable state is eagerly propagated to them upon their entrance (this
is identical to, and indeed just augments, the existing logic for the
propagation of the SAVEPOINT "stack").
A new GUC (citus.propagate_set_commands) has been added to control this
behavior. Though the code suggests the valid settings are 'none', 'local',
'session', and 'all', only 'none' (the default) and 'local' are presently
implemented: attempting to use other values will result in an error.
This is a preperation for the new executor, where creating shards
would go through the executor. So, explicitly generate the commands
for further processing.
Önder Kalacı
Philip Dubé
Hanefi Onaldi
Philip Dubé
Hadi Moshayedi
Hadi Moshayedi
Nils Dijk
Jason Petersen
Hanefi Onaldi
Marco Slot
Marco Slot