alternator/getting-started.md had a missing grave accent (`) character,
resulting in messed up rendering of the involved paragraph. Add the missing
quote.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200827110920.187328-1-nyh@scylladb.com>
We already have a docker image option to enable alternator on an unencrypted
port, "--alternator-port", but we forgot to also allow the similar option
for enabling alternator on an encrypted (HTTPS) port: "--alternator-https-port"
so this patch adds the missing option, and documents how to use it.
Note that using this option is not enough. When this option is used,
Alternator also requires two files, /etc/scylla/scylla.crt and
/etc/scylla/scylla.key, to be inserted into the image. These files should
contain the SSL certificate, and key, respectively. If these files are
missing, you will get an error in the log about the missing file.
Fixes#6583.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200621125219.12274-1-nyh@scylladb.com>
Correct the compatibility section in docs/alternator/alternator.md:
Filtering of Scan/Query results using the older syntax (ScanFilter,
QueryFilter) is, after commit bea9629031,
now fully supported. The newer syntax (FilterExpression) is not yet.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200604073207.416860-1-nyh@scylladb.com>
Alternator supports four ways in which write operations can use quorum
writes or LWT or both, which we called "write isolation policies".
Until this patch, Alternator defaulted to the most generally safe policy,
"always_use_lwt". This default could have been overriden for each table
separately, but there was no way to change this default for all tables.
This patch adds a "--alternator-write-isolation" configuration option which
allows changing the default.
Moreover, @dorlaor asked that users must *explicitly* choose this default
mode, and not get "always_use_lwt" without noticing. The previous default,
"always_use_lwt" supports any workload correctly but because it uses LWT
for all writes it may be disappointingly slow for users who run write-only
workloads (including most benchmarks) - such users might find the slow
writes so disappointing that they will drop Scylla. Conversely, a default
of "forbid_rmw" will be faster and still correct, but will fail on workloads
which need read-modify-write operations - and suprise users that need these
operations. So Dor asked that that *none* of the write modes be made the
default, and users must make an informed choice between the different write
modes, rather than being disappointed by a default choice they weren't
aware of.
So after this patch, Scylla refuses to boot if Alternator is enabled but
a "--alternator-write-isolation" option is missing.
The patch also modifies the relevant documentation, adds the same option to
our docker image, and the modifies the test-running script
test/alternator/run to run Scylla with the old default mode (always_use_lwt),
which we need because we want to test RMW operations as well.
Fixes#6452
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200524160338.108417-1-nyh@scylladb.com>
Some statements made in docs/alternator/alternator.md on having a single
keyspace, or recommending a DNS setup, are not up-to-date. So fix them.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200517132444.9422-1-nyh@scylladb.com>
The existing text did not explain what happens if additional DCs are added
to the cluster, so this patch improves the explanation of the status of
our support for global tables, including that issue.
Fixes#6353
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200513175908.21642-1-nyh@scylladb.com>
The "current compatibility with DynamoDB" section in alternator.md is where
we should list very briefly our state of compatibility - it's not the right
place to explain implementation details or track obscure bugs. I've
significantly shortened the "Tags" section because, in brief, we do
fully support tags and should say that we do.
I moved the two bugs mentioned in the text into the bug tracker:
Refs #6389
Refs #6391
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200507125022.22608-1-nyh@scylladb.com>
Alternator supports four different write isolation policies, the default
being to do all the writes with LWT, but these policies were only briefly
explained in alternator.md.
This patch significantly expands on this explanation, better explaining
the tradeoffs involved in these four options, and when each might make
sense (if at all).
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200506235152.18190-1-nyh@scylladb.com>
After fixing issue #6260, the "parallel scan" feature in Alternator is
supported, so drop the sentence in alternator.md saying that it isn't.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200422090738.21648-1-nyh@scylladb.com>
Merged patch series from Piotr Sarna:
This series allows reading rows from Scylla's system tables
via alternator by using a virtual interface.
If a Query or Scan request intercepts a table name with the following
pattern: .scylla.alternator.KEYSPACE_NAME.TABLE_NAME, it will read
the data from Scylla's KEYSPACE_NAME.TABLE_NAME table.
The interface is expected to only return data for Scylla system tables
and trying to access regular tables via this interface is expected
to return an error.
This series comes with tests (alternator-test, scylla_only).
Fixes#6122
Tests: alternator-test(local,remote (to verify that scylla_only works)
Piotr Sarna (5):
alternator: add fallback serialization for all types
alternator: add fetching static columns if they exist
alternator: add a way of accessing system tables from alternator
alternator-test: add scylla-only test for querying system tables
docs: add an entry about accessing Scylla system tables
alternator-test/test_system_tables.py | 61 +++++++++++++++++++++++++++
alternator/executor.cc | 38 ++++++++++++++++-
alternator/executor.hh | 1 +
alternator/serialization.cc | 11 +++--
docs/alternator/alternator.md | 15 +++++++
5 files changed, 122 insertions(+), 4 deletions(-)
create mode 100644 alternator-test/test_system_tables.py
Clean up the alternator.md document, by:
* Updating out-of-date information that outstayed its welcome.
* When Scylla does have a feature but it's just not supported via the
DynamoDB API (e.g., CDC and on-demand backups) mention that.
* Remove mention of Alternator being experimental and users should not
store important data on it :-)
* Miscellaneous cleanups.
Fixes#6179.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200412094641.27186-1-nyh@scylladb.com>
Since commit 9948f548a5, the LWT no longer
requires an "experimental" flag, so Alternator documents and scripts
which referred to the need for enabling experimental LWT, are fixed here
to no longer do that.
Fixes#6118.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200405143237.12693-1-nyh@scylladb.com>
Recently, Materialized Views were modified (see issue #4365) so that local
view updates (when both base and view replicas are the same node) are
synchronous. In particular, when the view's partition key is the same as
the base table's, view writes are synchronous: A write now only returns
after CL copies of the view data have been written.
Alternator's LSI have exactly this case (same partition key as the base).
This makes strongly-consistent (CL=LOCAL_QUORUM) reads in Alternator work
correctly, so we update the documentation accordingly to no longer say
that we don't support this DynamoDB feature.
However unlike LSIs, for GSIs strongly-consistent reads are still not
supported, and should not be supported (they are also not supported by
DynamoDB). Such reads should generate an error. So this patch fixes this
too. A GSI test which tested that strongly consistent reads are forbidden,
which used to xfail, now passes so the patch removes the "xfail".
Finally, we can simplify the LSI tests by using consistent reads instead of
eventually-consistent reads with retries. Beyond simplifying the test, it's
also an opportunity to *use* strongly-consistent reads and make sure that
they work (while, as mentioned above, similar reads for GSIs are refused).
Fixes#5007
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200311170446.28611-1-nyh@scylladb.com>
This patch completes the support for the ReturnValues parameter for
the UpdateItem operation. This parameter has five settings - NONE, ALL_OLD,
ALL_NEW, UPDATED_OLD and UPDATED_NEW. Before this patch we already
supported NONE and ALL_OLD - and this patch completes the support for the
three remaining modes: ALL_NEW, UPDATED_OLD and UPDATED_NEW.
The patch also continues to improve test_returnvalues.py with additional
corner cases discovered during the development. After this patch, only
one xfailing test remains - testing updates to nested document paths,
which we do not yet support (even without the ReturnValues parameter).
After this patch, the support of ReturnValues is complete - for all
operations (UpdateItem, PutItem and DeleteItem) and all of its possible
settings.
Fixes#5053
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200221224221.31237-5-nyh@scylladb.com>
In the state of Alternator in docs/alternator/alternator.md, we said that
BatchWriteItem doesn't check for duplicate entries. That is not true -
we do - and we even have tests (test_batch_write_duplicate*) to verify that.
So drop that comment.
Refs #5698. (there is still a small bug in the duplicate checking, so still
leaving that issue open).
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200219164107.14716-1-nyh@scylladb.com>
The instructions in docs/alternator/getting-started.md on how to run
Alternator with docker are outdated and confusing, so this patch updates
them.
First, the instructions recommended the scylladb/scylla-nightly:alternator
tag, but we only ever created this tag once, and never updated it. Since
then, Alternator has been constantly improving, and we've caught up on
a lot of features, and people who want to test or evaluate Alternator
will most likely want to run the latest nightly build, with all the latest
Alternator features. So we update the instructions to request the latest
nightly build - and mention the need to explictly do "docker pull" (without
this step, you can find yourself running an antique nightly build, which
you downloaded months ago!). This instruction can be revisited once
Alternator is GAed and not improving quickly and we can then recommend to
run the latest stable Scylla - but I think we're not there yet.
Second, in recent builds, Alternator requires that the LWT feature is
enabled, and since LWT is still experimental, this means that one needs
to add "--experimental 1" to the "docker run" command. Without it, the
command line in getting-started.md will refuse to boot, complaining that
Alternator was enabled but LWT wasn't. So this patch adds the
"--experimental 1" in the relevant places in the text. Again, this
instruction can and should be revisited once LWT goes out of experimental
mode.
Fixes#5813
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20200216113601.9535-1-nyh@scylladb.com>
This patch adds support for the ConditionExpression parameter of the
item-writing operations in Alternator: PutItem, UpdateItem and DeleteItem.
We already supported conditional updates/put/delete using the "Expected"
parameter. The ConditionExpression parameter implemented here provides a
very similar feature, using a different - and also newer and more powerful -
syntax.
The implementation here reuses much of our existing expression-parsing
infrastructure. Unsurprisingly, ConditionExpression's syntax has much in
common with UpdateExpression which we already support) and also many of the
comparison functions already implemented for "Expected". However, it's still
quite a bit of new code, because of the many different comparisons, functions,
and syntax variations we need to support.
This patch also expands alternator-test/test_condition_expression.py with
a few additional corner cases discovered during the development of this
patch.
Almost all of the tests for this feature (35 out of 39) now pass.
Two tests still fail because we don't yet support nested attributes (this
is a missing feature across Alternator), and two tests fail because of minor
ideosyncracies in DynamoDB's error path that we chose not to duplicate
yet (but still remember the difference in the form of an xfailing test).
Fixes#5035
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
In this patch, we re-implement the three read-modify-write operations -
PutItem, UpdateItem, DeleteItem. All three operations may need to read the
item before writing it to support conditional updates (the "Expected"
parameter) and UpdateItem may also need the previous item's value for
its update expression (e.g., a user may ask to "set a=a+1" or "set a=b").
Before this patch, the implementation of RMW operations simply did a read,
and then a write - without any attempt to protect concurrent operations.
In this patch, Scylla's LWT mechanism (storage_proxy::cas()) is used
instead, to ensure that concurrent update operations are correctly
isolated even if they are conditional. This means that Alternator now
requires the experimental LWT feature to be enabled (and refuses to
boot if it isn't).
The version presented here is configured to always use LWT for *every*
write, regardless of whether it has a condition or not. So it will
will significantly slow down write-only workloads like YCSB. But the code
in this patch actually includes three other modes, which can be chosen by
setting an enum constant in the code. In the future we will want to let the
user configure this mode, globally, per table or per attribute.
Note that read requests are NOT modified, and work exactly as they did
before: i.e., strongly-consistent reads are done using a normal
CL=LOCAL_QUORUM read - not via LWT. I believe this is good enough given
Dynamo's guarantees, and critical for our read performance.
Also note that patch doesn't yet fix the BatchWriteItem operation.
Although BatchWriteItem does not support any RMW operations - just pure
writes - we may still need to do those pure writes using LWT. This
should be fixed in a follow-up patch.
Unfortunately, this patch involves a large amount of code movement and
reorganization, because:
1. The cas operation requires each operation to be made into an object,
with a separate apply() function, forcing a lot of code to move.
2. Moreover, we need to do this for three different operations (PutItem,
UpdateItem, DeleteItem) so to avoid massive code duplication, I had
to move some common code.
3. The cas operation also forced us to change some of the utility functions'
APIs.
The end result is that this patch focuses more on a compact and
understandable *end result* than it does on an easy to understand *patch*,
so reviewers - sorry about that.
All alternator-test/ tests pass with this patch (and also with all of the
different optional modes enabled). However, other than that, I did not yet
do any real isolation tests (are concurrent operations really isolated
correctly? or is LWT just faking it? :-) ), performance tests or stress
tests - and I'll definitely need to do those as well.
Fixes#5054
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
The example Python code had wrong indentation, and wouldn't actually
work if naively copy-pasted. Noticed by Noam Hasson.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20190929091440.28042-1-nyh@scylladb.com>
This patch adds a getting started document for alternator,
it explains how to start up a cluster that has an alternator
API port open and how to test that it works using either an
application or some simple and minimal python scripts.
The goal of the document is to get a user to have an up and
running docker based cluster with alternator support in the
shortest time possible.
As part of trying to make alternator more accessible
to users, we expect more documents to be created so
it seems like a good idea to give all of the alternator
docs their own directory.
