When we enable CDC on a table, Scylla creates a log table for it.
It has default properties, but the user may change them later on.
Furthermore, it's possible to detach that log table by simply
disabling CDC on the base table:
```cql
/* Create a table with CDC enabled. The log table is created. */
CREATE TABLE ks.t (pk int PRIMARY KEY) WITH cdc = {'enabled': true};
/* Detach the log table. */
ALTER TABLE ks.t WITH cdc = {'enabled': false};
/* Modify a property of the log table. */
ALTER TABLE ks.t_scylla_cdc_log WITH bloom_filter_fp_chance = 0.13;
```
The log table can also be reattached by enabling CDC on the base table
again:
```cql
/* Reattach the log table */
ALTER TABLE ks.t WITH cdc = {'enabled': true};
```
However, because the process of reattachment goes through the same
code that created it in the first place, the properties of the log
table are rolled back to their default values. This may be confusing
to the user and, if unnoticed, also have other consequences, e.g.
affecting performance.
To prevent that, we ensure that the properties are preserved.
A reproducer test,
`test_log_table_preserves_properties_after_reattachment`, has been
provided to verify that the changes are correct. It fails before this
commit.
Another test, `test_log_table_preserves_id_after_reattachment`, has
also been added because the current implementation sets properties
and the ID separately.
Fixesscylladb/scylladb#25523
update cdc-related tests in test/cqlpy for cdc with tablets.
* test_cdc_log_entries_use_cdc_streams: this test depends on the
implementation of the cdc tables, which is different for tablets, so
it's changed to run for both vnodes and tablets keyspaces, and we add
the implementation for tablets.
* some cdc-related are unskipped for tablets so they will be run with
both tablets and vnodes keyspaces. these are tests where the
implementation may be different between tablets and vnodes and we want
to have converage of both.
* other cdc-related tests do not depend on the implementation
differences between tablets and vnodes, so we can just enable them to
run with the default configuration. previously they were disabled for
tablets keyspaces because it wasn't supported, so now we remove this.
Normally, when we create a table, MV, etc., we apply `cf_prop_defs` to the
schema builder via the function `cf_prop_defs::apply_to_builder`. Unfortunately,
that didn't happen when creating CDC log tables, and so we might have missed
some of the properties that would normally be set to some value, even if the
default one.
One particular example of that phenomenon was `tombstone_gc`. For better or
worse, it's not a "standalone property" of a table, but rather part of
`extensions`. [Somewhat related issue: scylladb/scylladb#9722]
That may have and did cause trouble. Consider this scenario:
1. A CDC log table is created.
2. The table does NOT have any value of `tombstone_gc` set.
3. The user edits the table via `ALTER TABLE`. That statement treats the log
table just like any other one (at least as far as the relevant portion of the
logic is concerned). Among other things, it uses
`cf_prop_defs::apply_to_builder`, and as a result, the `tombstone_gc`
property is set to some value:
* the default one if the user doesn't specify it in the statement,
* a custom one if they do.
Why is that a problem?
First of all, it's confusing. When we perform a schema backup and a table uses
CDC, we include an ALTER statement for its corresponding CDC log table (for more
context, see issue scylladb/scylladb#18467 or commit
scylladb/scylladb@f12edbdd95).
There are two consequences for the user here:
1. If the log table had NOT been altered ever since it was created, the
statement will miss the `tombstone_gc` property as if it couldn't be set for
it at all. That's confusing!
2. If the log table HAD in fact been altered after its creation, the statement
will include the `tombstone_gc` property. That's even more confusing (why was
it not present the first time, but it is now?).
The `tombstone_gc` property should always be set to avoid confusion and
problematic edge cases in tests and to simply be consistent with how other
schema entities work.
The solution we employ is that we always set the property to the default
value. That includes the case when we reattach the log table to the base;
consider the following scenario:
1. Create a table with CDC enabled.
2. Detach the log table by performing `ALTER TABLE ... WITH cdc = {'enabled': false}`.
3. Change the `tombstone_gc` property of the log table.
4. Reattach the log table to the base in the same way as in step 2.
The expected result would be that the new value of `tombstone_gc` would be
preserved after reattaching the log table. However, that's not what will
happen. We decide to stay consistent with how other properties of a log
table behave, and we reset them after every reattachment. We might change that
in the future: see issue scylladb/scylladb#25523.
Two reproducer tests of scylladb/scylladb#25187 are included in the changes.
Fixesscylladb/scylladb#25187
When the user disables CDC on a table, the CDC log table is not removed.
Instead, it's detached from the base table, and it functions as a normal
table (with some differences). If that log table lives up to the point
when the user re-enabled CDC on the base table, instead of creating a new
log table, the old one is re-attached to the base.
For more context on that, see commit:
scylladb/scylladb@adda43edc7.
In this commit, we add validation tests that check whether the changes
on the base table after disabling CDC are reflected on the log table
after re-enabling CDC. The definition of the log table should be the same
as if CDC had never been disabled.
Closesscylladb/scylladb#25071
When CDC becomes disabled on the base table, the CDC log table
still exsits (cf. scylladb/scylladb@adda43edc7).
If it continues to exist up to the point when CDC is re-enabled
on the base table, no new log table will be created -- instead,
the old olg table will be *re-attached*.
Since we want to avoid situations when the definition of the log
table has become misaligned with the definition of the base table
due to actions of the user, we forbid modifying the set of columns
or renaming them in CDC log tables, even when they're inactive.
Validation tests are provided.
The set of columns of a CDC log table should be managed automatically
by Scylla, and the user should not have the ability to manipulate them
directly. That could lead to disastrous consequences such as a
segmentation fault.
In this commit, we're restricting those operations. We also provide two
validation tests.
One of the existing tests had to be adjusted as it modified the type
of a column in a CDC log table. Since the test simply verifies that
the user has sufficient permissions to perform `ALTER TABLE` on the log
table, the test is still valid.
Fixesscylladb/scylladb#24643
Python and Python developers don't like directory names to include a
minus sign, like "cql-pytest". In this patch we rename test/cql-pytest
to test/cqlpy, and also change a few references in other code (e.g., code
that used test/cql-pytest/run.py) and also references to this test suite
in documentation and comments.
Arguably, the word "test" was always redundant in test/cql-pytest, and
I want to leave the "py" in test/cqlpy to emphasize that it's Python-based
tests, contrasting with test/cql which are CQL-request-only approval
tests.
Fixes#20846
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
