Until this patch, we used the default_smp_service_group() when bouncing
Alternator requests between shards (which is needed for LWT).
This patch creates a new smp_service_group for this purpose, which is
limited to 5000 concurrent requests (the same limit used for CQL's
bounce_request_smp_service_group). The purpose of this limit is to avoid
many shards admitting a huge number of requests and bouncing all of them
to the same shard who now can't "unadmit" these requests.
Fixes#5664.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200304170825.27226-1-nyh@scylladb.com>
Parsing a request string into JSON happens as a first thing
in every request, so it can be performed before calling
any executor callbacks. The most important thing however,
is that making parsing a separate stage allows certain optimizations,
e.g. running all parsing in a single seastar thread, which allows
adding yields to rjson parsing later.
The original idea of prefixing alternator keyspace names with 'a#'
leveraged the fact that '#' is not a legal CQL character for keyspace
names. The idea is flawed though, since '#' proved to confuse
existing Scylla tools (e.g. nodetool).
Thus, the prefix is changed to more orthodox 'alternator_'.
It is possible to create such keyspaces with CQL as well, but then
the alternator CreateTable request would simply fail, because
the keyspace already exists, which is graceful enough.
Hiding alternator keyspaces and tables from CQL is another issue,
but there are other ways to distinguish them than a non-standard
prefix, e.g. tags.
Fixes#5883
Instead of a monolith alternator keyspace, each table creates its own
keyspace, named in the following pattern: `a#TABLE_NAME`.
The `a#` prefix contains an illegal CQL character in order to ensure
that these keyspaces are never created via CQL.
Multiple requests can use the same client_state simultaneously, so it is
not safe to use it as a container for a tracing state which is per
request. This is not yet an issue for the alternator since it creates
new client_state object for each request, but first of all it should not
and second trace state will be dropped from the client_state, by later
patch.
In order to minimize the use of exceptions during normal operations,
each request handler is now able to return either a proper JSON value,
or an instance of api_error, which indicates that something went wrong,
but without having to throw, catch and rethrow C++ exceptions.
This is especially important for conditional updates, since it's
expected to be common to return ConditionalCheckFailedException.
Message-Id: <d8996a0a270eb0d9db8fdcfb7046930b96781e69.1579515640.git.sarna@scylladb.com>
Alternator uses a sharded<executor> for handling execution of Alternator
requests on different shards. In this patch we make executor a subclass of
peering_sharded_service, to allow one of these executors to run an exector
method on a different shard: Any one of the shard-local executor instances
can call container() to get the full sharded<executor>.
We will need this capability later, when we need to bounce requests between
shards because of requirements of the storage_proxy::cas (LWT) code.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
We currently reserve the column name "attrs" for a map of attributes,
so the user is not allowed to use this name as a name of a key.
We plan to lift this reservation in a future patch, but until we do,
let's at least choose a more obscure name to forbid - in this patch ":attrs".
It is even less likely that a user will want to use this specific name
as a column name.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20190903133508.2033-1-nyh@scylladb.com>
Keeping an instance of client_state is a convenient way of being able
to use tracing for alternator. It's also currently used in paging,
so adding a client state to executor removes the need of keeping
a dummy value.
In CQL, before a user can create a table, they must create a keyspace to
contain this table and, among other things, specify this keyspace's RF.
But in the DynamoDB API, there is no "create keyspace" operation - the
user just creates a table, and there is no way, and no opportunity,
to specify the requested RF. Presumably, Amazon always uses the same
RF for all tables, most likely 3, although this is not officially
documented anywhere.
The existing code creates the keyspace during Scylla boot, with RF=1.
This RF=1 always works, and is a good choice for a one-node test run,
but was a really bad choice for a real cluster with multiple nodes, so
this patch fixes this choice:
With this patch, the keyspace creation is delayed - it doesn't happen
when the first node of the cluster boots, but only when the user creates
the first table. Presumably, at that time, the cluster is already up,
so at that point we can make the obvious choice automatically: a one-node
cluster will get RF=1, a >=3 node cluster will get RF=3. The choice of
RF is logged - and the choice of RF=1 is considered a warning.
Note that with this patch, keyspace creation is still automatic as it
was before. The user may manually create the keyspace via CQL, to
override this automatic choice. In the future we may also add additional
keyspace configuration options via configuration flags or new REST
requests, and the keyspace management code will also likely change
as we start to support clusters with multiple regions and global
tables. But for now, I think the automatic method is easiest for
users who want to test-drive Alternator without reading lengthy
instructions on how to set up the keyspace.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20190820180610.5341-1-nyh@scylladb.com>
This patch adds to Alternator an implementation of the BatchGetItem
operation, which allows to start a number of GetItem requests in parallel
in a single request.
The implementation is almost complete - the only missing feature is the
ability to ask only for non-top-level attributes in ProjectionExpression.
Everything else should work, and this patch also includes tests which,
as usual, pass on DynamoDB and now also on Alternator.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Add support for the DeleteItem operation, which deletes an item.
The basic deletion operation is supported. Still not supported are:
1. Parameters to conditionally delete (ConditionalExpression or Expected)
2. Parameters to return pre-delete content
3. ReturnItemCollectionMetrics (statistics relevant for tables with LSI)
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
his patch adds a statistics framework to Alternator: Executor has (for
each shard) a _stats object which contains counters for various events,
and also is in charge of making these counters visible via Scylla's regular
metrics API (http://localhost:9180/metrics).
This patch includes a counter for each of DynamoDB's operation types,
and we increase the ones we support when handled. We also added counters
for total operations and unsupported operations (operation types we don't
yet handle). In the future we can easily add many more counters: Define
the counter in stats.hh, export it in stats.cc, and increment it in
where relevant in executor.cc (or server.cc).
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Instead of blindly returning "localhost:8000" in response to
DescribeEndpoints and for sure causing us problems in the future,
the right thing to do is to return the same domain name which the
user originally used to get to us, be it "localhost:8000" or
"some.domain.name:1234". But how can we know what this domain name
was? Easy - this is why HTTP 1.1 added a mandatory "Host:" header,
and the DynamoDB driver I tested (boto3) adds it as expected,
indeed with the expected value of "localhost:8000" on my local setup.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
DescribeEndpoints is not a very important API (and by default, clients
don't use it) but I wanted to understand how DynamoDB responds to it,
and what better way than to write a test :-)
And then, if we already have a test, let's implement this request in
Scylla as well. This is a silly implementation, which always returns
"localhost:8000". In the future, this will need to be configurable -
we're not supposed here to return *this* server's IP address, but rather
a domain name which can be used to get to all servers.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
So far we supported UpdateItem only with PUT operations - this patch
adds support for DELETE operations, to delete specific attributes from
an item.
Only the case of a missing value is support. DynamoDB also provides
the ability to pass the old value, and only perform the deletion if
the value and/or its type is still up-to-date - but we don't support
this yet and fail such request if it is attempted.
This patch also includes a test for this case in alternator-test/
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Add an initial UpdateItem implementation. As PutItem and GetItem we
are still limited to string attributes. This initial implementation
of UpdateItem implements only the "PUT" action (not "DELETE" and
certainly not "ADD") and not any of the more advanced options.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Add an initial implementation of Delete table, enough for making the
pytest --local test_table.py::test_create_and_delete_table
Pass.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
This initial implementation is enough to pass a test of getting a
failure for a non-existant table -
test_table.py::test_describe_table_non_existent_table
and to recognize an existing table. But it's still missing a lot
of fields for an existing table (among others, the schema).
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
The interface works on port 8000 by default and provides
the most basic alternator operations - it's an incomplete
set without validation, meant to allow testing as early as possible.
