This patch implements the previously-unimplemented Select option of the
Query and Scan operators.
The most interesting use case of this option is Select=COUNT which means
we should only count the items, without returning their actual content.
But there are actually four different Select settings: COUNT,
ALL_ATTRIBUTES, SPECIFIC_ATTRIBUTES, and ALL_PROJECTED_ATTRIBUTES.
Five previously-failing tests now pass, and their xfail mark is removed:
* test_query.py::test_query_select
* test_scan.py::test_scan_select
* test_query_filter.py::test_query_filter_and_select_count
* test_filter_expression.py::test_filter_expression_and_select_count
* test_gsi.py::test_gsi_query_select_1
These tests cover many different cases of successes and errors, including
combination of Select and other options. E.g., combining Select=COUNT
with filtering requires us to get the parts of the items needed for the
filtering function - even if we don't need to return them to the user
at the end.
Because we do not yet support GSI/LSI projection (issue #5036), the
support for ALL_PROJECTED_ATTRIBUTES is a bit simpler than it will need
to be in the future, but we can only finish that after #5036 is done.
Fixes#5058.
The most intrusive part of this patch is a change from attrs_to_get -
a map of top-level attributes that a read needs to fetch - to an
optional<attrs_to_get>. This change is needed because we also need
to support the case that we want to read no attributes (Select=COUNT),
and attrs_to_get.empty() used to mean that we want to read *all*
attributes, not no attributes. After this patch, an unset
optional<attrs_to_get> means read *all* attributes, a set but empty
attrs_to_get means read *no* attributes, and a set and non-empty
attrs_to_get means read those specific attributes.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20220405113700.9768-2-nyh@scylladb.com>
The document docs/alternator/compatibility.md suggested that Alternator
does not support the TTL feature at all. The real situation is more
optimistic - this feature is supported, but as experimental feature.
So let's update compatibility.md with the real status of this feature.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Now that issues #7586 and #9487 were fixed, reverse queries - even in
long partitions - work well, we can drop the claim in
alternator/docs/compatibility.md that reverse queries are buggy for
large partitions.
We can also remove the "xfail" mark from the tes that checks this
feature, as it now passes.
Refs #7586
Refs #9487
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes#9831
In the last year, four new features were added to DynamoDB which we
don't yet support - Kinesis Streams, PartiQL, Contributor Insights and
Export to S3. Let's document them as missing Alternator features, and
point to the four newly-created issues about these features.
Refs #8786
Refs #8787
Refs #8788
Refs #8789
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20210603125825.1179171-1-nyh@scylladb.com>
We had Alternator's current compatibility with DynamoDB described in
two places - alternator.md and compatibility.md. This duplication was
not only unnecessary, in some places it led to inconsistent claims.
In general, the better description was in compatibility.md, so in
this patch we remove the compatibility section from alternator.md
and instead link to compatibility.md. There was a bit of information
that was missing in compatibility.md, so this patch adds it.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20210215203057.1132162-1-nyh@scylladb.com>
This patch adds full support for nested attribute paths (e.g., a.b[3].c)
in UpdateExpression. After in previous patches we already added such
support for ProjectionExpression, ConditionExpression and FilterExpression
this means the nested attribute paths feature is now complete, so we
remove the warning from the documents. However, there is one last loose
end to tie and we will do it in the next patch: After this patch, the
combination of UpdateExpression with nested attributes and ReturnValues
is still wrong, and the test for it in test_returnvalues.py still xfails.
Note that previous patches already implemented support for attribute paths
in expression evaluations - i.e., the right-hand side of UpdateExpression
actions, and in this patch we just needed to implement the left hand side:
When an update action is on an attribute a.b we need to read the entire
content of the top-level a (an RWM operation), modify just the b part of
its json with the result of the action, and finally write back the entire
content of a. Of course everything gets complicated by the fact that we
can have multiple actions on multiple pieces of the same JSON, and we also
need to detect overlapping and conflicting actions (we already have this
detection in the attribute_path_map<> class we introduced in a previous
patch).
I decided to leave one small esoteric difference, reproduced by the xfailing
test_update_expression.py::test_nested_attribute_remove_from_missing_item:
As expected, "SET x.y = :val" fails for an item if its attribute x doesn't
exist or the item itself does not exist. For the update expression
"REMOVE x.y", DynamoDB fails if the attribute x doesn't exist, but oddly
silently passes if the entire item doesn't exist. Alternator does not
currently reproduce this oddity - it will fail this write as well.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Add to the DynamoDB compatibility document, docs/alternator/compatibility.md,
a mention that Alternator streams are still an experimental features, and
how to turn it on (at this point CDC is no longer an experimental feature,
but Alternator Streams are).
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20201112184436.940497-1-nyh@scylladb.com>
This patch adds a new document, docs/alternator/compatibility.md,
which focuses on what users switching from DynamoDB to Alternator
need to know about where Alternator differs from DynamoDB and which
features are missing.
The compatibility information in the old alternator.md is not deleted
yet. It probably should.
Fixes#7556
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20201110180242.716295-1-nyh@scylladb.com>
