Until now, every PutItem operation appeared in the Alternator Streams as
two events - a REMOVE and a MODIFY. DynamoDB Streams emits only INSERT
or MODIFY, depending on whether a row was replaced, or created anew. A
related issue scylladb#6918 concerns distinguishing the mutation type properly.
This was because each call to PutItem emitted the two CDC rows, returned
by GetRecords. Since this patch, we use a collection tombstone for the
`:attrs` column, and a separate tombstone for each regular column in the
table's schema. We don't expect that new tables would have any other
regular column, except for the `:attrs` and keys, but we may encounter
them in in upgraded tables which had old GSIs or LSIs.
Fixes: scylladb#6930.
Closesscylladb/scylladb#24991
Moved files:
- generic_server.hh
- generic_server.cc
- protocol_server.hh
Fixes: #22112
This is a cleanup, no need to backport
Closesscylladb/scylladb#25090
Until recently, Seastar's HTTP server's reply::write_body() only
supported a few "well-known" content types. But Alternator uses a
lesser known one - "application/x-amz-json-1.0" - so it was forced to
use a *wrong* (but legal) content type, and later override it with the
correct one. This was really ugly and we had a comment that once this
feature was fixed in Seastar, we should remove the ugly workaround.
Well, the time has finally come. We can now finally pass the correct
content type to write_body(), and don't need to call the deprecated
type-changing function later.
The new implementation is less awkward, but actually longer - whereas
previously we only set the content type in one place - just before
the done(), after this patch we actually need to do it in three places
where we write the body (string response, streaming response and
error response). But I think this is actually better - there is no
inherent reason why, for example, error messages and success messages
needed to use the same content type. We use a new constant
REPLY_CONSTANT_TYPE so that we don't need to repeat it three times.
We already have a regression test for the content-type returned by
Alternator, test_manual_requests.py::test_content_type, and this
test continues to pass after the patch. But this test only checked
the short response path, so we add additional tests for the streaming
response path and for the error response path. As usual, the new
tests pass on DynamoDB as well.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closesscylladb/scylladb#26268
Before this patch, every expression in Alternator's requests was parsed from string to adequate structure.
This patch enables caching - all calls to parse an expression (all types) are proxied through the cache.
New expression is added to the cache, the least recently used entry (above cache size) is removed.
For existing entries the copy of the template is returned - individual instances still need to be resolved (placeholders substituted with names and values).
The cache is per shard - shared for all operations, expression types, tables, users.
Default cache size is 2000 entries per shard and it has configuration option `alternator_max_expression_cache_entries_per_shard` (0 means cache disabled).
Added Python tests are based on metrics.
Every expression in Alternator's requests is parsed from string to adequate structure.
This patch implements a caching structure (input expression strings mapping to parsed 'template' structures), which will be used for handling requests in following commits.
If the reqested expression is valid (parsable) the cache will always return a value - if it is not already in the cache it will be created and stored.
The cache has limited (live configurable) size - when it is reached, the least recently used entry is removed.
The copy of the template in cache is returned - individual instances still need to be resolved (placeholders substituted with names and values).
Invalid requests will have no effect on the cache - the parser throws an exception.
Caching is implemented for all expression types. Internally it is based on helper structure `lru_string_map`.
Basic metrics (total count of hits and misses for each expression type and number of evictions) are implemented.
Metrics are used in boost unit tests.
With this patch empty update expression is no longer accepted by the parser.
So far it was rejected only after resolving, however it could pollute the expression cache.
Primitive conditions usually use operator with two or more values.
The only case of a "single value" condition is a function call -
DynamoDB does not accept other general values (i.e., attribute or value references).
In Alternator single general value was parsed as correct and only failed
later when the calculated value ended up to not be a boolean.
This works, but not when attribute or value actually is boolean.
What is more, when a parsed (but not resolved) expression is cached, this invalid expression could pollute cache.
This would be also the only case where the same string can be parsed both as a condition and a projection expression.
The issue is fixed by explicitly checking this case at primitive condition parsing.
Updated test confirms consistence between Alternator and DynamoDB.
Fixes#25855.
Before this patch, if an ARN that is passed to Alternator requests
like TagResource is well-formatted but points to non-existent table,
Alternator returns the unhelpful error:
(AccessDeniedException) when calling the TagResource operation:
Incorrect resource identifier
This patch modifies this error to be:
(ResourceNotFoundException) when calling the TagResource operation:
ResourceArn 'arn:scylla:alternator:alternator_alternator_Test_
1758532308880:scylla:table/alternator_Test_1758532308880x' not found
This is the same error type (ResourceNotFoundException) that DynamoDB
returns in that case - and a more helpful error message.
This patch also includes a regression test that checks the error
type in this case. The new test fails on Alternator before this
patch, and passes afterwards (and also passes on DyanamoDB).
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closesscylladb/scylladb#26179
As requested in #22104, moved the files and fixed other includes and build system.
Moved files:
- combine.hh
- collection_mutation.hh
- collection_mutation.cc
- converting_mutation_partition_applier.hh
- converting_mutation_partition_applier.cc
- counters.hh
- counters.cc
- timestamp.hh
Fixes: #22104
This is a cleanup, no need to backport
Closesscylladb/scylladb#25085
update all the references about the issue of tablets support for
alternator streams to issue #23838 instead of #16317.
The issue #16317 is about support of CDC with tablets, but it is now
closed and it didn't address alternator streams. the remaining issues
about alternator streams should be addressed as part of #23838, so fix
the references in order for them not to be missed.
Previously, LSI keys were stored as separate, top-level columns in the base table. This patch changes this behavior for newly created tables, so that the key columns are stored inside the `:attrs` map. Then, we use top-level computed columns instead of regular ones.
This makes LSI storage consistent with GSIs and allows the use of a collection tombstone on `:attrs` to delete all attributes in a row except for keys in new tables.
Refs https://github.com/scylladb/scylladb/pull/24991
Refs https://github.com/scylladb/scylladb/issues/6930Closesscylladb/scylladb#25796
* github.com:scylladb/scylladb:
alternator: Store LSI keys in :attrs for newly created tables
alternator/test: Add LSI tests based mostly on the existing GSI tests
Alternator, when creating gsi, adds artificially columns, that user
had not ask for. This patch prevents those columns from showing up in
DescribeTable's output.
Fixes#5320Closesscylladb/scylladb#25978
In test/alternator/test_returnvalues.py we had tests for the
ReturnValues feature on UpdateItem requests - but we only tested
UpdateItem requests with the "modern" UpdateExpression, and forgot to
test the combination of ReturnValues with the old AttributeUpdates API.
It turns out this combination is buggy: when both ReturnValues=ALL_OLD
and AttributeUpdates need the previous value of the item, we may wrongly
std::move() the value out, and the operation will fail with a strange
error:
An error occurred (ValidationException) when calling the UpdateItem
operation: JSON assert failed on condition 'IsObject()'
The fix in this patch is trivial - just move the std::move() to the
correct place, after both UpdateExpression and AttributeUpdates
handling is done.
This patch also includes a reproducing test, which fails before this
patch and passes with it - and of course passes on DynamoDB. This
test reproduces two cases where the bug happened, as well as one
case where it didn't (to make sure we don't regress in what already
worked).
Fixes#25894
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closesscylladb/scylladb#25900
This patch overrides the antlr3 function that allocates the missing
tokens that would eventually leak. The override stores these tokens in
a vector, ensuring memory is freed whenever the parser is destroyed.
Solution is copied from CQL implementation.
A unit test to reproduce the issue is added - leak would be reported
by ASAN, when running this test in debug mode - the test passed but
the leak is discovered when the test file exits.
Fixes#25878Closesscylladb/scylladb#25930
As requested in #22120, moved the files and fixed other includes and build system.
Moved files:
- query.cc
- query-request.hh
- query-result.hh
- query-result-reader.hh
- query-result-set.cc
- query-result-set.hh
- query-result-writer.hh
- query_id.hh
- query_result_merger.hh
Fixes: #22120
This is a cleanup, no need to backport
Closesscylladb/scylladb#25105
In the DynamoDB API, when "a" is a list attribute, a[999] returns the
1000th element. But if the list isn't that long (e.g., it only has 5
elements), a[999] returns nothing - it's not an error.
But it turns out that when the index is so long that it can't even be
parsed as an integer, e.g., 99999999999999, DynamoDB does report an
error:
Invalid ProjectionExpression: List index is not within the
allowable range; index: [99999999999999]
Before this patch, Alternator also returned an error in this case,
with the right type (ValidationException), but with a strange low-level
error text:
Failed parsing ProjectionExpression 'a[99999999999999]':
std::out_of_range (stoi)
The problem was that the code (in alternator/expressions.g) ran stoi()
without converting its std::out_of_range exception to a better user-facing
message. We do this in this patch, and the error message now looks like:
Failed parsing ProjectionExpression 'a[99999999999999]':
list index out of integer range
This patch also includes a test reproducing this error, which passes
on DynamDB and on Alternator it fails before this patch and passes with
the patch.
Fixes#25947
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closesscylladb/scylladb#25951
Alternator needs to store a few pieces of information for each table
that it can't store in the existing CQL schema. We decided to store
this information in hidden tags - tags named with the prefix "system:" -
and we already have four of those: Provisioned RCU and WCU, table
creation time, and TTL's expiration-time attribute.
This patch moves the definition of all four tags to one place in
executor.cc, adds a short comment about the content of each tag,
and adds a longer comment explaining why we have these hidden tags
at all.
It is expected that more hidden tags will follow - e.g., to solve
issue #5320. So we expect more tags to be added later in the same
place in the code.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closesscylladb/scylladb#25980
Before this patch, LSI keys were stored as separate, top-level columns
in the base table. This patch changes this behavior for newly created
tables, so that the key columns are stored inside the `:attrs` map.
Then, in the LSI's materialized view, we create a computed column for
each LSI's range key that is not a key in the base table.
This makes LSI storage consistent with GSIs and allows the use of a
collection tombstone on `:attrs` to delete all fields in a row, except
for keys, in new tables.
Refs https://github.com/scylladb/scylladb/pull/24991
Refs https://github.com/scylladb/scylladb/issues/6930
This commit adds missing fields to GetRecords responses: `awsRegion` and
`eventVersion`. We also considered changing `eventSource` from
`scylladb:alternator` to `aws:dynamodb` and setting `SizeBytes` subfield
inside the `dynamodb` field.
We set `awsRegion` to the datacenter's name of the node that received
the request. This is in line with the AWS documentation, except that
Scylla has no direct equivalent of a region, so we use the datacenter's
name, which is analogous to DynamoDB's concept of region.
The field `eventVersion` determines the structure of a Record. It is
updated whenever the structure changes. We think that adding a field
`userIdentity` bumped the version from `1.0` to `1.1`. Currently, Scylla
doesn't support this field (#11523), hence we use the older 1.0 version.
We have decided to leave `eventSource` as is, since it's easy to modify
it in case of problems to `aws:dynamodb` used by DynamoDB.
Not setting `SizeBytes` subfield inside the `dynamodb` field was
dictated by the lack of apparent use cases. The documentation is unclear
about how `SizeBytes` is calculated and after experimenting a little
bit, I haven't found an obvious pattern.
Fixes: #6931Closesscylladb/scylladb#24903
This patch introduces `view_building_coordinator`, a single entity within whole cluster responsible for building tablet-based views.
The view building coordinator takes slightly different approach than the existing node-local view builder. The whole process is split into smaller view building tasks, one per each tablet replica of the base table.
The coordinator builds one base table at a time and it can choose another when all views of currently processing base table are built.
The tasks are started by setting `STARTED` state and they are executed by node-local view building worker. The tasks are scheduled in a way, that each shard processes only one tablet at a time (multiple tasks can be started for a shard on a node because a table can have multiple views but then all tasks have the same base table and tablet (last_token)). Once the coordinator starts the tasks, it sends `work_on_view_building_tasks` RPC to start the tasks and receive their results.
This RPC is resilient to RPC failure or raft leader change, meaning if one RPC call started a batch of tasks but then failed (for instance the raft leader was changed and caller aborted waiting for the response), next RPC call will attach itself to the already started batch.
The coordinator plugs into handling tablet operations (migration/resize/RF change) and adjusts its tasks accordingly. At the start of each tablet operation, the coordinator aborts necessary view building tasks to prevent https://github.com/scylladb/scylladb/issues/21564. Then, new adjusted tasks are created at the end of the operation.
If the operation fails at any moment, aborted tasks are rollback.
The view building coordinator can also handle staging sstables using process_staging view building tasks. We do this because we don't want to start generating view updates from a staging sstable prematurely, before the writes are directed to the new replica (https://github.com/scylladb/scylladb/issues/19149).
For detailed description check: `docs/dev/view-building-coordinator.md`
Fixes https://github.com/scylladb/scylladb/issues/22288
Fixes https://github.com/scylladb/scylladb/issues/19149
Fixes https://github.com/scylladb/scylladb/issues/21564
Fixes https://github.com/scylladb/scylladb/issues/17603
Fixes https://github.com/scylladb/scylladb/issues/22586
Fixes https://github.com/scylladb/scylladb/issues/18826
Fixes https://github.com/scylladb/scylladb/issues/23930
---
This PR is reimplementation of https://github.com/scylladb/scylladb/pull/21942Closesscylladb/scylladb#23760
* github.com:scylladb/scylladb:
test/cluster: add view build status tests
test/cluster: add view building coordinator tests
utils/error_injection: allow to abort `injection_handler::wait_for_message()`
test: adjust existing tests
utils/error_injection: add injection with `sleep_abortable()`
db/view/view_builder: ignore `no_such_keyspace` exception
docs/dev: add view building coordinator documentation
db/view/view_building_worker: work on `process_staging` tasks
db/view/view_building_worker: register staging sstable to view building coordinator when needed
db/view/view_building_worker: discover staging sstables
db/view/view_building_worker: add method to register staging sstable
db/view/view_update_generator: add method to process staging sstables instantly
db/view/view_update_generator: extract generating updates from staging sstables to a method
db/view/view_update_generator: ignore tablet-based sstables
db/view/view_building_coordinator: update view build status on node join/left
db/view/view_building_coordinator: handle tablet operations
db/view: add view building task mutation builder
service/topology_coordinator: run view building coordinator
db/view: introduce `view_building_coordinator`
db/view/view_building_worker: update built views locally
db/view: introduce `view_building_worker`
db/view: extract common view building functionalities
db/view: prepare to create abstract `view_consumer`
message/messaging_service: add `work_on_view_building_tasks` RPC
service/topology_coordinator: make `term_changed_error` public
db/schema_tables: create/cleanup tasks when an index is created/dropped
service/migration_manager: cleanup view building state on drop keyspace
service/migration_manager: cleanup view building state on drop view
service/migration_manager: create view building tasks on create view
test/boost: enable proxy remote in some tests
service/migration_manager: pass `storage_proxy` to `prepare_keyspace_drop_announcement()`
service/migration_manager: coroutinize `prepare_new_view_announcement()`
service/storage_proxy: expose references to `system_keyspace` and `view_building_state_machine`
service: reload `view_building_state_machine` on group0 apply()
service/vb_coordinator: add currently processing base
db/system_keyspace: move `get_scylla_local_mutation()` up
db/system_keyspace: add `view_building_tasks` table
db/view: add view_building_state and views_state
db/system_keyspace: add method to get view build status map
db/view: extract `system.view_build_status_v2` cql statements to system_keyspace
db/system_keyspace: move `internal_system_query_state()` function earlier
db/view: ignore tablet-based views in `view_builder`
gms/feature_service: add VIEW_BUILDING_COORDINATOR feature
Add precompiled header support to CMakeLists.txt and configure.py -
it improves compilation time by approximately 10%.
New header `stdafx.hh` is added, don't include it manually -
the compiler will include it for you. The header contains includes from
external libraries used by Scylla - seastar, standard library,
linux headers and zlib.
The feature is enabled by default, use CMake option `Scylla_USE_PRECOMPILED_HEADER`
or configure.py --disable-precompiled-header to disable.
The feature should be disabled, when trying to check headers - otherwise
you might get false negatives on missing includes from seastar / abseil and so on.
Note: following configuration needs to be added to ccache.conf:
sloppiness = pch_defines,time_macros
Closes#25182
std::views::trasform()s should not have side effects since they could be
called several times, depending on the algorithm they're paired with.
For example, std::ranges::to() can run the algorithm once to measure
the resulting container size, and then a second time to copy the data
(avoiding reallocations). If that happens, then the side-effect happens
twice.
Avoid this be refactoring the code. Make the side-effect -- appending
to the `column` vector -- happen first, then use that result to generate
the `regular_column` vector.
In this case, the side effect did not happen twice because small_vector's
std::from_range_t constructor only reserves if the input range is sized
(and it is not), but better not have the weakness in the code.
Closesscylladb/scylladb#25011
This series adds support for a DynamoDB-compatible Write Capacity Unit (WCU) calculation in Alternator by introducing an optional forced read-before-write mechanism.
Alternator's model differs from DynamoDB, and as a result, some write operations may report lower WCU usage compared to what DynamoDB would report. While this is acceptable in many cases, there are scenarios where users may require accurate WCU reporting that aligns more closely with DynamoDB's behavior.
To address this, a new configuration option, alternator_force_read_before_write, is introduced. When enabled, Alternator will perform a read before executing PutItem, UpdateItem, and DeleteItem operations. This allows it to take the existing item size into account when computing the WCU. BatchWriteItem support is also extended to use this mechanism. Because BatchWriteItem does not support returning old items directly, several internal changes were made to support reading previous item sizes with minimal overhead. Reads are performed at consistency level LOCAL_ONE for efficiency, and the WCU calculation is now done in multiple stages to accurately account for item size differences.
In addition to the implementation changes, test coverage was added to validate the new behavior. These tests confirm that WCU is calculated based on the larger of the old and new items when read-before-write is active, including for BatchWriteItem.
This feature comes with performance overhead and is therefore disabled by default. It can be enabled at runtime via the system.config table and should be used only when precise WCU tracking is necessary.
**New feature, no need to backport**
Closesscylladb/scylladb#24436
* github.com:scylladb/scylladb:
alternator/test_returnconsumedcapacity.py: Test forced read before write
alternator/executor.cc: DynamoDB WCU calculation in BatchWriteItem using read-before-write
executor.cc: get_previous_item with consistency level
executor: Extend API of put_or_delete_item
alternator/executor.cc: Accurate WCU for put, update, delete
config: add alternator_force_read_before_write
Alternator's internal model differs from DynamoDB, which can result in
lower WCU (Write Capacity Unit) estimates for some operations. While this
is often acceptable, accurate WCU tracking is occasionally required.
This patch enables a DynamoDB like WCU calculation for `BatchWriteItem` when the
`alternator_force_read_before_write` configuration is enabled, by reading
existing items before applying changes.
WCU calculation in `BatchWriteItem` is now performed in three stages:
1. During the initial scan, no calculation is done, just the pointers
are collected.
2. If read-before-write is enabled, each item is read again and its
prior size is compared to the new value. WCU is based on the larger
of the two. The updated size is stored in the mutation building
array.
3. Regardless of read-before-write, metrics are updated and consumed
capacity units are returned if requested. This is done in a loop
before sending the mutations.
For performance, reads in `BatchWriteItem` use consistency level LOCAL_ONE.
These changes increase WCU DynamoDB compatibility in batch operations,
but add overhead and should be enabled only when needed.
Signed-off-by: Amnon Heiman <amnon@scylladb.com>
Some callers, like `construct_range_to_endpoint_map` for describe_ring,
or `get_secondary_ranges` for alternator ttl pass vnode tokens (the
vnodes' start token), and therefore can benefit from the fast lookup
path in `vnode_effective_replication_map::do_get_replicas`.
Otherwise the vnode token is binary-searched in sorted_tokens using
token_metadata::first_token().
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
In commit 44a1daf we added the ability to read Scylla system tables with Alternator. This feature is useful, among other things, in tests that want to read Scylla's configuration through the system table system.config. But tests often want to modify system.config, e.g., to temporarily reduce some threshold to make tests shorter. Until now, this was not possible
This series add supports for writing to system tables through Alternator, and examples of tests using this capability (and utility functions to make it easy).
Because the ability to write to system tables may have non-obvious security consequences, it is turned off by default and needs to be enabled with a new configuration option "alternator_allow_system_table_write"
No backports are necessary - this feature is only intended for tests. We may later decide to backport if we want to backport new tests, but I think the probability we'll want to do this is low.
Fixes#12348Closesscylladb/scylladb#19147
* github.com:scylladb/scylladb:
test/alternator: utility functions for changing configuration
alternator: add optional support for writing to system table
test/alternator: reduce duplicated code
This patch extends get_previous_item so it can be used to calculate the
size of a previous item. This will allow batch_get_item to obtain the
size of a previous item without needing the item itself.
The patch includes the following changes:
* Removes the unneeded forward declaration of get_previous_item.
* Extends get_previous_item to accept an explicit consistency level.
* Modifies the regular get_previous_item to maintain the same
functionality while calling the base implementation.
* Adds a get_previous_item_size function that uses the base
implementation to retrieve the size of a previous item when only the
size is needed. For performance reasons, get_previous_item_size uses
consistency level one.
Signed-off-by: Amnon Heiman <amnon@scylladb.com>
Derive both vnode_effective_replication_map
and local_effective_replication_map from
static_effective_replication_map as both are static and per-keyspace.
However, local_effective_replication_map does not need vnodes
for the mapping of all tokens to the local node.
Note that everywhere_replication_strategy is not abstracted in a similar
way, although it could, since the plan is to get rid of it
once all system keyspaces areconverted to local or tablets replication
(and propagated everywhere if needed using raft group0)
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
to static_effective_replication_map_ptr, in preparation
for separating local_effective_replication_map from
vnode_effective_replication_map.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
to get_static_effective_replication_map, in preparation
for separating local_effective_replication_map from
vnode_effective_replication_map (both are per-keyspace).
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Prepare for following patch that will separate
the local effective replication map from
vnode_effective_replication_map.
The caller is responsible to keep the
effective_replication_map_ptr alive while
in use by low-level async functions.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
In commit 44a1daf we added the ability to read system tables through
the DynamoDB API (actually, the Scan and Query requests only).
This ability is useful for tests, and can also be useful to users who
want to read information that is only available through system tables.
This patch adds support also for *writing* into system tables. This will
be useful for Alternator tests, were we want to temporarily change
some live-updatable configuration option - and so far haven't been
able to do that like we did do in some cql-pytest tests.
For reasons explained in issue #23218, only superuser roles are allowed to
write to system tables - it is not enough for the role to be granted
MODIFY permissions on the system table or on ALL KEYSPACES. Moreover,
the ability to modify system tables carries special risks, so this
patch only allows writes to the system tables if a new configuration
option "alternator_allow_system_table_write" turned on. This option is
turned off by default.
This patch also includes a test for this new configuration-writing
capability. The test scripts test/alternator/run and test.py now
run Scylla with alternator_allow_system_table_write turned on, but
the new test can also run without this option, and will be skipped
in that case (to allow running the test suite against some manually-
run instance of Scylla).
Fixes: #12348
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
This patch adds two methods to put_or_delete_item that will be used in
WCU batch calculation:
A setter to set the item length.
A boolean getter that determines if this is a delete action.
To improve the accuracy of Write Capacity Unit (WCU) calculation,
this patch introduces the use of the `alternator_force_read_before_write`
configuration option. When enabled, it forces a read-before-write
operation on `PutItem`, `UpdateItem`, and `DeleteItem` requests.
This comes with performance overhead and should be used with caution,
especially in high-throughput environments.
Today, the "system.clients" virtual table lists active connections (and
their various properties, like client address, logged in username and
client version) only for CQL requests. In this patch we make Alternator
active clients also be listed on this virtual table.
Unlike CQL where logged in username applies to a complete connection,
in the Alternator API, different requests, theoretically signed by
different users, can arrive over the same HTTP connection. So instead of
listing the currently open *connections*, we list the currently active
*requests*.
This means that when scanning system.clients, you will only see requests
which are being handled right now - and not inactive HTTP connections.
I think this good enough (besides being the correct thing to do) - one
of the goals of this system.clients is to be able to see what kind of
drivers are being used by the user (the "driver_name" field in the
system.clients) - on a busy server there will always be some (even many)
requests being handled, so we'll always have plenty of requests to see
in system.clients.
By the way, note that for Alternator requests, what we use for the
"driver_name" is the request's User-Agent header. AWS SDKs typically
write the driver's name, its version, and often a lot of other
information in that header. For example, Boto3 sends a User-Agent
looking like:
Boto3/1.38.46 md/Botocore#1.38.46 md/awscrt#0.24.2
ua/2.1 os/linux#6.15.4-100.fc41.x86_64 md/arch#x86_64
lang/python#3.13.5 md/pyimpl#CPython m/N,P,b,D,Z
cfg/retry-mode#legacy Botocore/1.38.46 Resource
A functional test for the new feature - adding Alternator requests to
the system.clients table - will be in the next patch.
Fixes#24993
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
As requested in #22102, #22103 and #22105 moved the files and fixed other includes and build system.
Moved files:
- clustering_bounds_comparator.hh
- keys.cc
- keys.hh
- clustering_interval_set.hh
- clustering_key_filter.hh
- clustering_ranges_walker.hh
- compound_compat.hh
- compound.hh
- full_position.hh
Fixes: #22102Fixes: #22103Fixes: #22105Closesscylladb/scylladb#25082
Rather than calling std::views::transform with a lambda that extracts
a member from a class, call std::views::transform with a pointer-to-member
to do the same thing. This results in more concise code.
Closesscylladb/scylladb#25012
This series fixes one cause of oversized allocations - and therefore potentially stalls and increased tail latencies - in Alternator.
The first patch in the series is the main fix - the later patches are cleanups requested by reviewers but also involved other pre-existing code, so I did those cleanups as separate patches.
Alternator's Scan or Query operation return a page of results. When the number of items is not limited by a "Limit" parameter, the default is to return a 1 MB page. If items are short, a large number of them can fit in that 1MB. The test test_query.py::test_query_large_page_small_rows has 30,000 items returned in a single page.
In the response JSON, all these items are returned in a single array "Items". Before this patch, we build the full response as a RapidJSON object before sending it. The problem is that unfortunately, RapidJSON stores arrays as contiguous allocations. This results in large contiguous allocations in workloads that scan many small items, and large contiguous allocations can also cause stalls and high tail latencies. For example, before this patch, running
test/alternator/run --runveryslow \
test_query.py::test_query_large_page_small_rows
reports in the log:
oversized allocation: 573440 bytes.
After this patch, this warning no longer appears.
The patch solves the problem by collecting the scanned items not in a RapidJSON array, but rather in a chunked_vector<rjson::value>, i.e, a chunked (non-contiguous) array of items (each a JSON value). After collecting this array separately from the response object, we need to print its content without actually inserting it into the object - we add a new function print_with_extra_array() to do that.
The new separate-chunked-vector technique is used when a large number (currently, >256) of items were scanned. When there is a smaller number of items in a page (this is typical when each item is longer), we just insert those items in the object and print it as before.
Beyond the original slow test that demonstrated the oversized allocation (which is now gone), this patch also includes a new test which exercises the new code with a scan of 700 (>256) items in a page - but this new test is fast enough to be permanently in our test suite and not a manual "veryslow" test as the other test.
Fixes#23535
The stalls caused by large allocations was seen by actual users, so it makes sense to backport this patch. On the other hand, the patch while not big is fairly intrusive (modifies the nomal Scan and Query path and also the later patches do some cleanup of additional code) so there is some small risk involved in the backport.
Closesscylladb/scylladb#24480
* github.com:scylladb/scylladb:
alternator: clean up by co-routinizing
alternator: avoid spamming the log when failing to write response
alternator: clean up and simplify request_return_type
alternator: avoid oversized allocation in Query/Scan
Before this series, it is possible to crash Scylla (due to an I/O error) by creating an Alternator table close to the maximum name length of 222, and then enabling Alternator Streams. This series fixes this bug in two ways:
1. On a pre-existing table whose name might be up to 222 characters, enabling Streams will check if the resulting name is too long, and if it is, fail with a clear error instead of crashing. This case will effect pre-existing tables whose name has between 207 and 222 characters (207 is `222 - strlen("_scylla_cdc_log")`) - for such tables enabling Streams will fail, but no longer crash.
2. For new tables, the table name length limit is lowered from 222 to 192. The new limit is still high enough, but ensures it will be possible to enable streams any new table. It will also always be possible to add a GSI for such a table with name up to 29 characters (if the table name is shorter, the GSI name can be longer - the sum can be up to 221 characters).
No need to backport, Alternator Streams is still an experimental feature and this patch just improves the unlikely situation of extremely long table names.
Fixes#24598Closesscylladb/scylladb#24717
* github.com:scylladb/scylladb:
alternator: lower maximum table name length to 192
alternator: don't crash when adding Streams to long table name
alternator: split length limit for regular and auxiliary tables
alternator: avoid needlessly validating table name
Reviewers of the previous patch complained on some ugly pre-existing
code in alternator/executor.cc, where returning from an asynchronous
(future) function require lengthy verbose casts. So this patch cleans
up a few instances of these ugly casts by using co_return instead of
return.
For example, the long and verbose
return make_ready_future<executor::request_return_type>(
rjson::print(std::move(response)));
can be changed to the shorter and more readable
co_return rjson::print(std::move(response));
This patch should not have any functional implications, and also not any
performance implications: I only coroutinized slow-path functions and
one function that was already "partially" coroutinized (and this was
expecially ugly and deserved being fixed).
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Both make_streamed() and new make_streamed_with_extra_array() functions,
used when returning a long response in Alternator, would write an error-
level log message if it failed to write the response. This log message
is probably not helpful, and may spam the log if the application causes
repeated errors intentionally or accidentally.
So drop these log messages. The exception is still thrown as usual.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
The previous patch introduced a function make_streamed_with_extra_array
which was a duplicate of the existing make_streamed. Reviewers
complained how baroque the new function is (just like the old function),
having to jump through hoops to return a copyable function working
on non-copyable objects, making strange-named copies and shared pointers
of everything.
We needed to return a copyable function (std::function) just because
Alternator used Seastar's json::json_return_type in the return type
from executor function (request_return_type). This json_return_type
contained either a sstring or an std::function, but neither was ever
really appropriate:
1. We want to return noncopyable_function, not an std::function!
2. We want to return an std::string (which rjson::print()) returns,
not an sstring!
So in this patch we stop using seastar::json::json_return_type
entirely in Alternator.
Alternator's request_return_type is now an std::variant of *three* types:
1. std::string for short responses,
2. noncopyable_function for long streamed response
3. api_error for errors.
The ugliest parts of make_streamed() where we made copies and shared
pointers to allow for a copyable function are all gone. Even nicer, a
lot of other ugly relics of using seastar::json_return_type are gone:
1. We no longer need obscure classes and functions like make_jsonable()
and json_string() to convert strings to response bodies - an operation
can simply return a string directly - usually returning
rjson::print(value) or a fixed string like "" and it just works.
2. There is no more usage of seastar::json in Alternator (except one
minor use of seastar::json::formatter::to_json in streams.cc that
can be removed later). Alternator uses RapidJSON for its JSON
needs, we don't need to use random pieces from a different JSON
library.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
This patch fixes one cause of oversized allocations - and therefore
potentially stalls and increased tail latencies - in Alternator.
Alternator's Scan or Query operation return a page of results. When the
number of items is not limited by a "Limit" parameter, the default is
to return a 1 MB page. If items are short, a large number of them can
fit in that 1MB. The test test_query.py::test_query_large_page_small_rows
has 30,000 items returned in a single page.
In the response JSON, all these items are returned in a single array
"Items". Before this patch, we build the full response as a RapidJSON
object before sending it. The problem is that unfortunately, RapidJSON
stores arrays as contiguous allocations. This results in large
contiguous allocations in workloads that scan many small items, and
large contiguous allocations can also cause stalls and high tail
latencies. For example, before this patch, running
test/alternator/run --runveryslow \
test_query.py::test_query_large_page_small_rows
reports in the log:
oversized allocation: 573440 bytes.
After this patch, this warning no longer appears.
The patch solves the problem by collecting the scanned items not in a
RapidJSON array, but rather in a chunked_vector<rjson::value>, i.e,
a chunked (non-contiguous) array of items (each a JSON value).
After collecting this array separately from the response object, we
need to print its content without actually inserting it into the object -
we add a new function print_with_extra_array() to do that.
The new separate-chunked-vector technique is used when a large number
(currently, >256) of items were scanned. When there is a smaller number
of items in a page (this is typical when each item is longer), we just
insert those items in the object and print it as before.
Beyond the original slow test that demonstrated the oversized allocation
(which is now gone), this patch also includes a new test which
exercises the new code with a scan of 700 (>256) items in a page -
but this new test is fast enough to be permanently in our test suite
and not a manual "veryslow" test as the other test.
Fixes#23535
Currently, Alternator allows creating a table with a name up to 222
(max_table_name_length) characters in length. But if you do create
a table with such a long name, you can have some difficulties later:
You you will not be able to add Streams or GSI or LSI to that table,
because 222 is also the absolute maximum length Scylla tables can have
and the auxilliary tables we want to create (CDC log, materialized views)
will go over this absolute limit (max_auxiliary_table_name_length).
This is not nice. DynamoDB users assume that after successfully
creating a table, they can later - perhaps much later - decide to
add Streams or GSI to it, and today if they chose extremely long
names, they won't be able to do this.
So in this patch, we lower max_table_name_length from 222 to 192.
A user will not be able to create tables with longer names, but
the good news is that once successfully creating a table, it will
always be possible to enable Streams on it (the CDC log table has an
extra 15 bytes in its name, and 192 + 15 is less than 222), and it
will be possible to add GSIs with short enough names (if the GSI
name is 29 or less, 192 + 29 + 1 = 222).
This patch is a trivial one-line code change, but also includes the
corrected documentation of the limits, and a fix for one test that
previously checked that a table name with length 222 was allowed -
and now needs to check 192 because 222 is no longer allowed.
Note that if a user has existing tables and upgrades Scylla, it
is possible that some pre-existing Alternator tables might have
lengths over 192 (up to 222). This is fine - in the previous patches
we made sure that even in this case, all operations will still work
correctly on these old tables (by not not validating the name!), and
we also made sure that attempting to enable Streams may fail when
the name is too long (we do not remove those old checks in this patch,
and don't plan to remove them in the forseeable future).
Note that the limit we chose - 192 characters - is identical to the
table name limit we recently chose in CQL. It's nicer that we don't
need to memorize two different limits for Alternator and CQL.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
