* Require superuser while activating a node
With this change, we require ActiveNode() (hence citus_add_node(),
citus_activate_node()) explicitly require for a superuser.
Before this commit, these functions were designed to work with
non-superuser roles with the relevent GRANTs given.
However, that is not a widely used way for calling the functions
above.
Due to possibility of non-super user calling the UDFs, they were
designed in a way that some commands were using some additional
short-lived superuser connections. That is:
(a) breaking transactional behavior (e.g., ROLLBACK
wouldn't fully rollback the whole transaction)
(b) Making it very complicated to reason about which
parts of the node activation goes over which connections,
and becoming vulnerable to deadlocks / visibility issues.
In addition to starting a new transaction, we also need to tell other
backends --including the ones spawned for connections opened to
localhost to build indexes on shards of this relation-- that concurrent
index builds can safely ignore us.
Normally, DefineIndex() only does that if index doesn't have any
predicates (i.e.: where clause) and no index expressions at all.
However, now that we already called standard process utility, index
build on the shell table is finished anyway.
The reason behind doing so is that we cannot guarantee not grabbing any
snapshots via adaptive executor, and the backends creating indexes on
local shards (if any) might block on waiting for current xact of the
current backend to finish, which would cause self deadlocks that are not
detectable.
With https://github.com/citusdata/citus/pull/5493 we introduced
metadata specific connections.
With this connection we guarantee that there is a single metadata connection.
But note that this connection can be used for any other operation.
In other words, this connection is not only reserved for metadata
operations.
However, as https://github.com/citusdata/citus-enterprise/issues/715 showed
us that the logic has a flaw. We allowed ineligible connections to be
picked as metadata connections: such as exclusively claimed connections
or not fully initialized connections.
With this commit, we make sure that we only consider eligable connections
for metadata operations.
We prefer the background daemon to only sync node metadata. That's
why we move placement metadata changes from disable node to
activate node. With that, we can make sure that disable node
only changes node metadata, whereas activate node syncs all
the metadata changes. In essence, we already expect all
nodes to be up when a node is activated. So, this does not change
the behavior much.
Dropping sequences means we need to recreate
and hence losing the sequence.
With this commit, we keep the existing sequences
such that resyncing wouldn't drop the sequence.
We do that by breaking the dependency of the sequence
from the table.
Split distributed/version_compat.h into dependency-free
pg_version_compat.h, and the original which still has
dependencies. The original doesn't have much purpose, but until other
files have better discipline about including the correct header files,
then it's still needed.
Also make distributed/listutils.h dependency-free. Should be moved
outside of 'distributed' subdirectory, but that will cause significant
code churn, so leave for another cleanup patch.
Now both files can be included in columnar without creating a
dependency on citus.
Previously, we cheated by using the RM_GENERIC_ID record type, but not
actually using the generic WAL API. This worked because we always took
a full page image, and saved the extra work of allocating and copying
to a temporary page.
But it introduced complexity, and perhaps fragility, so better to just
use the API properly. The performance penalty for a serial data load
seems to be less than 1%.
Before this commit, Citus was triggering metadata syncing
in the background when a function is distributed. However,
with Citus 11, we expect all clusters to have metadata synced
enabled. So, we do not expect any nodes not to have the metadata.
This change:
(a) pro: simplifies the code and opens up possibilities
to simplify futher by reducing the scope of
bg worker to only sync node metadata
(b) pro: explicitly asks users to sync the metadata such that
any unforseen impact can be easily detected
(c) con: For distributed functions without distribution
argument, we do not necessarily require the metadata
sycned. However, for completeness and simplicity, we
do so.
Burak Velioglu
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Onur Tirtir
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jeff-davis
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