The first and main issue was that we were putting absolute pointers into
shared memory for the `steps` field of the `ProgressMonitorData`. This
pointer was being overwritten every time a process requested the monitor
steps, which is the only reason why this even worked in the first place.
To quote a part of a relevant stack overflow answer:
> First of all, putting absolute pointers in shared memory segments is
> terrible terible idea - those pointers would only be valid in the
> process that filled in their values. Shared memory segments are not
> guaranteed to attach at the same virtual address in every process.
> On the contrary - they attach where the system deems it possible when
> `shmaddr == NULL` is specified on call to `shmat()`
Source: https://stackoverflow.com/a/10781921/2570866
In this case a race condition occurred when a second process overwrote
the pointer in between the first process its write and read of the steps
field.
This issue is fixed by not storing the pointer in shared memory anymore.
Instead we now calculate it's position every time we need it.
The second race condition I have not been able to trigger, but I found
it while investigating this. This issue was that we published the handle
of the shared memory segment, before we initialized the data in the
steps. This means that during initialization of the data, a call to
`get_rebalance_progress()` could read partial data in an unsynchronized
manner.
With a recent commit, we made (644b266dee)
the behaviour of prepared statements for local cached plans has
slightly changed.
Now, Citus caches the plans when they are re-used. This make triggering
of local cached plans on the 7th execution, and 8th execution is the
first time the plan is used from the cached.
So, the tests are improved to cover 8th execution.
With local query caching, we try to avoid deparse/parse stages as the
operation is too costly.
However, we can do deparse/parse operations once per cached queries, right
before we put the plan into the cache. With that, we avoid edge
cases like (4239) or (5038).
In a sense, we are making the local plan caching behave similar for non-cached
local/remote queries, by forcing to deparse the query once.
A shard move would fail if there was an orphaned version of the shard on
the target node. With this change before actually fail, we try to clean
up orphaned shards to see if that fixes the issue.
Sometimes the background daemon doesn't cleanup orphaned shards quickly
enough. It's useful to have a UDF to trigger this removal when needed.
We already had a UDF like this but it was only used during testing. This
exposes that UDF to users. As a safety measure it cannot be run in a
transaction, because that would cause the background daemon to stop
cleaning up shards while this transaction is running.
* Add user-defined sequence support for MX
* Remove default part when propagating to workers
* Fix ALTER TABLE with sequences for mx tables
* Clean up and add tests
* Propagate DROP SEQUENCE
* Removing function parts
* Propagate ALTER SEQUENCE
* Change sequence type before propagation & cleanup
* Revert "Propagate ALTER SEQUENCE"
This reverts commit 2bef64c5a29f4e7224a7f43b43b88e0133c65159.
* Ensure sequence is not used in a different column with different type
* Insert select tests
* Propagate rename sequence stmt
* Fix issue with group ID cache invalidation
* Add ALTER TABLE ALTER COLUMN TYPE .. precaution
* Fix attnum inconsistency and add various tests
* Add ALTER SEQUENCE precaution
* Remove Citus hook
* More tests
Co-authored-by: Marco Slot <marco.slot@gmail.com>
We have a slightly different behavior when using truncate_local_data_after_distributing_table UDF on metadata synced clusters. This PR aims to add tests to cover such cases.
We allow distributing tables with data that have foreign keys to reference tables only on metadata synced clusters. This is the reason why some of my earlier tests failed when run on a single node Citus cluster.
InvalidateForeignKeyGraph sends an invalidation via shared memory to all
backends, including the current one.
However, we might not call AcceptInvalidationMessages before reading
from the cache below. It would be better to also add a call to
AcceptInvalidationMessages in IsForeignConstraintRelationshipGraphValid.
Previously this was usually done after argument parsing. This can cause
SEGFAULTs if the number or type of arguments changes in a new version.
By checking that Citus version is correct before doing any argument
parsing we protect against these types of issues. Issues like this have
occurred in pg_auto_failover, so it's not just a theoretical issue.
The main reason why these calls were not at the top of functions is
really just historical. It was because in the past we didn't allow
statements before declarations. Thus having this check before the
argument parsing would have only been possible if we first declared all
variables.
In addition to moving existing CheckCitusVersion calls it also adds
these calls to rebalancer related functions (they were missing there).
The current default citus settings for tests are not really best
practice anymore. However, we keep them because lots of tests depend on
them.
I noticed that I created the same test harness for new tests I added all
the time. This is a simple script that generates that harness, given a
name for the test.
To run:
src/test/regress/bin/create_test.py my_awesome_test
To be able to report progress of the rebalancer, the rebalancer updates
the state of a shard move in a shared memory segment. To then fetch the
progress, `get_rebalance_progress` can be called which reads this shared
memory.
Without this change it did so without using any synchronization
primitives, allowing for data races. This fixes that by using atomic
operations to update and read from the parts of the shared memory that
can be changed after initialization.
Jelte Fennema
Onder Kalaci
Onur Tirtir
Hanefi Onaldi
SaitTalhaNisanci
Halil Ozan Akgul
Ahmet Gedemenli
Naisila Puka
Marco Slot