Update create-keyspace-statement section of ddl.rst since `class` is no longer mandatory.
Add an example for keyspace creation without specifying `class`.
Refs: #16029
This commit removes the Non-Reserved CQL Keywords and Reserved CQL Keywords pages-keyword
as that content is already covered on the Appendices page.
Redirections are added to avoid 404s for the removed pages.
In addition, the Appendices page title is extended with "Reserved CQL Keywords and Types"
to help users understand what those appendices are about.
Fixes https://github.com/scylladb/scylladb/issues/24319Closesscylladb/scylladb#24320
This commit increases the maximum length of names for keyspaces, tables, materialized views, and indexes from 48 to 192 bytes.
The previous 48-bytes limit was inherited from Cassandra 3 for compatibility. However, this validation was removed in Cassandra 4 and 5 (see CASSANDRA-20389)
and some usage scenarios (such as some feature store workflows generating long table names) now depend on this relaxed constraint.
This change brings ScyllaDB's behavior in line with modern Cassandra versions and better supports these use cases.
The new limit of 192 bytes is derived from underlying filesystem limitations to prevent runtime errors when creating directories for table data.
When a new table is created, ScyllaDB generates a directory for its SSTables. The directory name is constructed from the table name, a dash, and a 32-character UUID.
For a CDC-enabled table, an associated log table is also created, which has the suffix `_scylla_cdc_log` appended to its name.
The directory name for this log table becomes the longest possible representation.
Additionally we reserve 15 bytes for future use, allowing for potential future extensions without breaking existing schemas.
To guarantee that directory creation never fails due to exceeding filesystem name limits, the maximum name length is calculated as follows:
255 bytes (common filesystem limit for a path component)
- 32 bytes (for the 32-character UUID string)
- 1 byte (for the '-' separator)
- 15 bytes (for the '_scylla_cdc_log' suffix)
- 15 bytes (reserved for future use)
----------
= 192 bytes (Maximum allowed name length)
This calculation is similar in principle to the one proposed for Cassandra to fix related directory creation failures (see apache/cassandra/pull/4038).
This patch also updates/adds all associated tests to validate the new 192-byte limit.
The documentation has been updated accordingly.
Current protocol extension that sends tablet info to drivers only does
that if the driver selects a non-replica coordinator for a routable
request. It works well if some node on the replica list is replaced by
other node, or if some replicas are removed from the list. Driver will
at some point send a request to stale replica, and receive new list in
response.
The issue is with extending the list with new replicas. In that case old
replicas are all still correct, so driver will not select any wrong
replica, and will not receive the new list. As far as I know that only
scenario where this could happen is RF increase.
It could be to some degree worked around in the drivers, but it would
add significant complexity (definitely more than any other invalidations
we introduced) while still not being ideal solution. This scenario
should be rare enough, and the consequences of not handling it minor
enough (new replicas not being used as coordinators) that it does not
warrant driver-side solution. Instead this commit adds info about this
to documentation, advising users to restart applications after replica
lists are extended.
It is worth noting that if new tablet feedback protocol extension is
implemented then this problem goes away. See issue #21664.
Closesscylladb/scylladb#23447
We introduce a new term in the glossary: RF-rack-valid keyspace.
We also highlight in our user documentation that all keyspaces
must remain RF-rack-valid throughout their lifetime, and failing
to guarantee that may result in data inconsistencies or other
issues. We base that information on our experience with materialized
views in keyspaces using tablets, even though they remain
an experimental feature.
Along with the new term, we introduce a new configuration option
called `rf_rack_valid_keyspaces`, which, when enabled, will enforce
preserving all keyspaces RF-rack-valid. That functionality will be
implemented in upcoming commits. For now, we materialize the
restriction in form of a named requirement: a function verifying
that the passed keyspace is RF-rack-valid.
The option is disabled by default. That will change once we adjust
the existing tests to the new semantics. Once that is done, the option
will first be enabled by default, and then it will be removed.
Fixesscylladb/scylladb#20356
This commit adds a link to the Limitations section on the Tablets page
to the CQL pag, the tablets option.
This is actually the place where the user will need the information:
when creating a keyspace.
In addition, I've reorganized the section for better readability
(otherwise, the section about limitations was easy to miss)
and moved the section up on the page.
Note that I've removed the updated content from the `_common` folder
(which I deleted) to the .rst page - we no longer split OSS and Enterprise,
so there's no need to keep using the `scylladb_include_flag` directive
to include OSS- and Ent-specific content.
Fixes https://github.com/scylladb/scylladb/issues/22892
Fixes https://github.com/scylladb/scylladb/issues/22940Closesscylladb/scylladb#22939
Use the keyspace initial_tablets for min_tablet_count, if the latter
isn't set, then take the maximum of the option-based tablet counts:
- min_tablet_count
- and expected_data_size_in_gb / target_tablet_size
- min_per_shard_tablet_count (via
calculate_initial_tablets_from_topology)
If none of the hints produce a positive tablet_count,
fall back to calculate_initial_tablets_from_topology * initial_scale.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Per-table hints should be used instead.
Note: the warning is produced by check_against_restricted_replication_strategies
which is called also from alter_keyspace_statement.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Unlike with vnodes, each tablet is served only by a single
shard, and it is associated with a memtable that, when
flushed, it creates sstables which token-range is confined
to the tablet owning them.
On one hand, this allows for far better agility and elasticity
since migration of tablets between nodes or shards does not
require rewriting most if not all of the sstables, as required
with vnodes (at the cleanup phase).
Having too few tablets might limit performance due not
being served by all shards or by imbalance between shards
caused by quantization. The number of tabelts per table has to be
a power of 2 with the current design, and when divided by the
number of shards, some shards will serve N tablets, while others
may serve N+1, and when N is small N+1/N may be significantly
larger than 1. For example, with N=1, some shards will serve
2 tablet replicas and some will serve only 1, causing an imbalance
of 100%.
Now, simply allocating a lot more tablets for each table may
theoretically address this problem, but practically:
a. Each tablet has memory overhead and having too many tablets
in the system with many tables and many tablets for each of them
may overwhelm the system's and cause out-of-memory errors.
b. Too-small tablets cause a proliferation of small sstables
that are less efficient to acces, have higher metadata overhead
(due to per-sstable overhead), and might exhaust the system's
open file-descriptors limitations.
The options introduced in this change can help the user tune
the system in two ways:
1. Sizing the table to prevent unnecessary tablet splits
and migrations. This can be done when the table is created,
or later on, using ALTER TABLE.
2. Controlling min_per_shard_tablet_count to improve
tablet balancing, for hot tables.
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Add a paragraph documenting the decision to deprecate
the COMPACT STORAGE feature, and instruct the user
how to enable the feature despite that.
Note that we don't have an official migration strategy
for users like `DROP COMPACT STORAGE`, which is not
implemented at this time (See #3882).
Fixes#16375
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
ICS is a compaction strategy that inherits size tiered properties --
therefore it's write optimized too -- but fixes its space overhead of
100% due to input files being only released on completion. That's
achieved with the concept of sstable run (similar in concept to LCS
levels) which breaks a large sstable into fixed-size chunks (1G by
default), known as run fragments. ICS picks similar-sized runs
for compaction, and fragments of those runs can be released
incrementally as they're compacted, reducing the space overhead
to about (number_of_input_runs * 1G). This allows user to increase
storage density of nodes (from 50% to ~80%), reducing the cost of
ownership.
NOTE: test_system_schema_version_is_stable adjusted to account for batchlog
using IncrementalCompactionStrategy
contains:
compaction/: added incremental_compaction_strategy.cc (.hh), incremental_backlog_tracker.cc (.hh)
compaction/CMakeLists.txt: include ICS cc files
configure.py: changes for ICS files, includes test
db/legacy_schema_migrator.cc / db/schema_tables.cc: fallback to ICS when strategy is not supported
db/system_keyspace: pick ICS for some system tables
schema/schema.hh: ICS becomes default
test/boost: Add incremental_compaction_test.cc
test/boost/sstable_compaction_test.cc: ICS related changes
test/cqlpy/test_compaction_strategy_validation.py: ICS related changes
docs/architecture/compaction/compaction-strategies.rst: changes to ICS section
docs/cql/compaction.rst: changes to ICS section
docs/cql/ddl.rst: adds reference to ICS options
docs/getting-started/system-requirements.rst: updates sentence mentioning ICS
docs/kb/compaction.rst: changes to ICS section
docs/kb/garbage-collection-ics.rst: add file
docs/kb/index.rst: add reference to <garbage-collection-ics>
docs/operating-scylla/procedures/tips/production-readiness.rst: add ICS section
some relevant commits throughout the ICS history:
commit 434b97699b39c570d0d849d372bf64f418e5c692
Merge: 105586f747 30250749b8
Author: Paweł Dziepak <pdziepak@scylladb.com>
Date: Tue Mar 12 12:14:23 2019 +0000
Merge "Introduce Incremental Compaction Strategy (ICS)" from Raphael
"
Introduce new compaction strategy which is essentially like size tiered
but will work with the existing incremental compaction. Thus incremental
compaction strategy.
It works like size tiered, but each element composing a tier is a sstable
run, meaning that the compaction strategy will look for N similar-sized
sstable runs to compact, not just individual sstables.
Parameters:
* "sstable_size_in_mb": defines the maximum sstable (fragment) size
composing
a sstable run, which impacts directly the disk space requirement which is
improved with incremental compaction.
The lower the value the lower the space requirement for compaction because
fragments involved will be released more frequently.
* all others available in size tiered compaction strategy
HOWTO
=====
To change an existing table to use it, do:
ALTER TABLE mykeyspace.mytable WITH compaction =
{'class' : 'IncrementalCompactionStrategy'};
Set fragment size:
ALTER TABLE mykeyspace.mytable WITH compaction =
{'class' : 'IncrementalCompactionStrategy', 'sstable_size_in_mb' : 1000 }
"
commit 94ef3cd29a196bedbbeb8707e20fe78a197f30a1
Merge: dca89ce7a5 e08ef3e1a3
Author: Avi Kivity <avi@scylladb.com>
Date: Tue Sep 8 11:31:52 2020 +0300
Merge "Add feature to limit space amplification in Incremental Compaction" from Raphael
"
A new option, space_amplification_goal (SAG), is being added to ICS. This option
will allow ICS user to set a goal on the space amplification (SA). It's not
supposed to be an upper bound on the space amplification, but rather, a goal.
This new option will be disabled by default as it doesn't benefit write-only
(no overwrites) workloads and could hurt severely the write performance.
The strategy is free to delay triggering this new behavior, in order to
increase overall compaction efficiency.
The graph below shows how this feature works in practice for different values
of space_amplification_goal:
https://user-images.githubusercontent.com/1409139/89347544-60b7b980-d681-11ea-87ab-e2fdc3ecb9f0.png
When strategy finds space amplification crossed space_amplification_goal, it
will work on reducing the SA by doing a cross-tier compaction on the two
largest tiers. This feature works only on the two largest tiers, because taking
into account others, could hurt the compaction efficiency which is based on
the fact that the more similar-sized sstables are compacted together the higher
the compaction efficiency will be.
With SAG enabled, min_threshold only plays an important role on the smallest
tiers, given that the second-largest tier could be compacted into the largest
tier for a space_amplification_goal value < 2.
By making the options space_amplification_goal and min_threshold independent,
user will be able to tune write amplification and space amplification, based on
the needs. The lower the space_amplification_goal the higher the write
amplification, but by increasing the min threshold, the write amplification
can be decreased to a desired amount.
"
commit 7d90911c5fb3fa891ad64a62147c3a6ca26d61b1
Author: Raphael S. Carvalho <raphaelsc@scylladb.com>
Date: Sat Oct 16 13:41:46 2021 -0300
compaction: ICS: Add garbage collection
Today, ICS lacks an approach to persist expired tombstones in a timely manner,
which is a problem because accumulation of tombstones are known to affecting
latency considerably.
For an expired tombstone to be purged, it has to reach the top of the LSM tree
and hope that older overlapping data wasn't introduced at the bottom.
The condition are there and must be satisfied to avoid data resurrection.
STCS, today, has an inefficient garbage collection approach because it only
picks a single sstable, which satisfies the tombstone density threshold and
file staleness. That's a problem because overlapping data either on same tier
or smaller tiers will prevent tombstones from being purged. Also, nothing is
done to push the tombstones to the top of the tree, for the conditions to be
eventually satisfied.
Due to incremental compaction, ICS can more easily have an effecient GC by
doing cross-tier compaction of relevant tiers.
The trigger will be file staleness and tombstone density, which threshold
values can be configured by tombstone_compaction_interval and
tombstone_threshold, respectively.
If ICS finds a tier which meets both conditions, then that tier and the
larger[1] *and* closest-in-size[2] tier will be compacted together.
[1]: A larger tier is picked because we want tombstones to eventually reach the
top of the tree.
[2]: It also has to be the closest-in-size tier as the smaller the size
difference the higher the efficiency of the compaction. We want to minimize
write amplification as much as possible.
The staleness condition is there to prevent the same file from being picked
over and over again in a short interval.
With this approach, ICS will be continuously working to purge garbage while
not hurting overall efficiency on a steady state, as same-tier compactions are
prioritized.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20211016164146.38010-1-raphaelsc@scylladb.com>
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Closesscylladb/scylladb#22063
Although `crc_check_chance` is accepted as a configuration option in ScyllaDB,
the value is currently ignored during runtime. This change makes this behavior
explicit in the documentation to prevent potential user misunderstandings.
Changes:
- Explicitly document that the option is currently a no-op
- Provide clear guidance on the current implementation
- Prevent confusion about the option's actual functionality
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#21794
ScyllaDB doesn't support custom compressors. The available compressors
are the only available ones, not the default ones.
Adjust the text to reflect this.
Closesscylladb/scylladb#20225
This commit extracts the information about the default for tables in keyspace creation
to a separate file in the _common folder. The file is then included using
the scylladb_include_flag directive.
The purpose of this commit is to make it possible to include a different file
in the scylla-enterprise repo - with a different default.
Refs https://github.com/scylladb/scylla-enterprise/issues/4585Closesscylladb/scylladb#20181
This commit removes the information that tablets are an experimental feature
from the CREATE KEYSPACE section.
In addition, it removes the notes and cautions that are redundant when
a feature is GA, especially the information and warnings about the future
plans.
Fixes https://github.com/scylladb/scylladb/issues/18670Closesscylladb/scylladb#19063
This change supports changing replication factor in tablets-enabled keyspaces.
This covers both increasing and decreasing the number of tablets replicas through
first building topology mutations (`alter_keyspace_statement.cc`) and then
tablets/topology/schema mutations (`topology_coordinator.cc`).
For the limitations of the current solution, please see the docs changes attached to this PR.
Fixes: #16129Closesscylladb/scylladb#16723
* github.com:scylladb/scylladb:
test: Do not check tablets mutations on nodes that don't have them
test: Fix the way tablets RF-change test parses mutation_fragments
test/tablets: Unmark RF-changing test with xfail
docs: document ALTER KEYSPACE with tablets
Return response only when tablets are reallocated
cql-pytest: Verify RF is changes by at most 1 when tablets on
cql3/alter_keyspace_statement: Do not allow for change of RF by more than 1
Reject ALTER with 'replication_factor' tag
Implement ALTER tablets KEYSPACE statement support
Parameterize migration_manager::announce by type to allow executing different raft commands
Introduce TABLET_KEYSPACE event to differentiate processing path of a vnode vs tablets ks
Extend system.topology with 3 new columns to store data required to process alter ks global topo req
Allow query_processor to check if global topo queue is empty
Introduce new global topo `keyspace_rf_change` req
New raft cmd for both schema & topo changes
Add storage service to query processor
tablets: tests for adding/removing replicas
tablet_allocator: make load_balancer_stats_manager configurable by name
In order to correctly restore schema from `DESC SCHEMA WITH INTERNALS`, we need a way to drop a column with a timestamp in the past.
Example:
- table t(a int pk, b int)
- insert some data1
- drop column b
- add column b int
- insert some data2
If the sstables weren't compacted, after restoring the schema from description:
- we will loss column b in data2 if we simply do `ALTER TABLE t DROP b` and `ALTER TABLE t ADD b int`
- we will resurrect column b in data1 if we skip dropping and re-adding the column
Test for this: https://github.com/scylladb/scylla-dtest/pull/4122Fixes#16482Closesscylladb/scylladb#18115
* github.com:scylladb/scylladb:
docs/cql: update ALTER TABLE docs
test/cqlpytest: add test for prepared `ALTER TABLE ... DROP ... USING TIMESTAMP ?`
test/cql-pytest: remove `xfail` from alter table with timestamp tests
cql3/statements: extend `ALTER TABLE ... DROP` to allow specifying timestamp of column drop
cql3/statements: pass `query_options` to `prepare_schema_mutations()`
cql3/statements: add bound terms to alter table statement
cql3/statements: split alter_table_statement into raw and prepared
schema: allow to specify timestamp of dropped column
dclocal_read_repair_chance and read_repair_chance have been removed in Cassandra 3.11 and 4.x, see
https://issues.apache.org/jira/browse/CASSANDRA-13910. if we expose these properties via DDL, Cassandra would fail to consume the CQL statement creating the table when performing migration from Scylla to Cassandra 4.x, as the latter does not understand these properties anymore.
currently the default values of `dc_local_read_repair_chance` and `read_repair_chance` are both "0". so they are practically disabled, unless user deliberately set them to a value greater than 0.
also, as a side effect, Cassandra 4.x has better support of Python3. the cqlsh shipped along with Cassandra 3.11.16 only supports python2.7, see
https://github.com/apache/cassandra/blob/cassandra-3.11.16/bin/cqlsh.py it errors out if the system only provides python3 with the error of
```
No appropriate python interpreter found.
```
but modern linux systems do not provide python2 anymore.
so, in this change, we deprecate these two options.
Fixes#3502
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#18087
* github.com:scylladb/scylladb:
docs: drop documents related to {,dclocal_}read_repair_chance
treewide: remove {dclocal_,}read_repair_chance options
since "read_repair_chance" and "dclocal_read_repair_chance" are
removed, and not supported anymore. let's stop documenting them.
Refs #3502
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Currently, if tombstone_gc mode isn't specified for a table,
then "timeout" is used by default. With tablets, running
"nodetool repair -pr" may miss a tablet if it migrated across
the nodes. Then, if we expire tombstones for ranges that
weren't repaired, we may get data resurrection.
Set default tombstone_gc mode value for DDLs that don't
specify it. It's set to "repair" for tables which use tablets
unless they use local replication strategy or rf = 1.
Otherwise it's set to "timeout".
Now the user can do
CREATE KEYSPACE ... WITH TABLETS = { 'enabled': false }
to turn tablets off. It will be useful in the future to opt-out keyspace
from tablets when they will be turned on by default based on cluster
features only.
Also one can do just
CREATE KEYSPACE ... WITH TABLETS = { 'enabled': true }
and let Scylla select the initial tablets value by its own
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
This patch changes the syntax of enabling tablets from
CREATE KEYSPACE ... WITH REPLICATION = { ..., 'initial_tablets': <int> }
to be
CREATE KEYSPACE ... WITH TABLETS = { 'initial': <int> }
and updates all tests accordingly.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
This commit adds information on how to enable
object storage for a keyspace.
The "Keyspace storage options" section already
existed in the doc, but it was not valid as
the support was only added in version 5.4
The scope of this commit:
- Update the "Keyspace storage options" section.
- Add the information about object storage support
to the Data Definition> CREATE KEYSPACE section
* Marked as "Experimental".
* Excluded from the Enterprise docs with the
.. only:: opensource directive.
This commit must be backported to branch-5.4,
as support for object storage was added
in version 5.4.
Closesscylladb/scylladb#16081
The goal is to make the available defaults safe for future use, as they
are often taken from existing config files or documentation verbatim.
Referenced issue: #14290Closesscylladb/scylladb#15856
Fixes https://github.com/scylladb/scylladb/issues/14598
This commit adds the description of minimum_keyspace_rf
to the CREATE KEYSPACE section of the docs.
(When we have the reference section for all ScyllaDB options,
an appropriate link should be added.)
This commit must be backported to branch-5.3, because
the feature is already on that branch.
Closes#14686
The chunk size used in sstable compression can be set when creating a
table, using the "chunk_length_in_kb" parameter. It can be any power-of-two
multiple of 1KB. Very large compression chunks are not useful - they
offer diminishing returns on compression ratio, and require very large
memory buffers and reading a very large amount of disk data just to
read a small row. In fact, small chunks are recommended - Scylla
defaults to 4 KB chunks, and Cassandra lowered their default from 64 KB
(in Cassandra 3) to 16 KB (in Cassandra 4).
Therefore, allowing arbitrarily large chunk sizes is just asking for
trouble. Today, a user can ask for a 1 GB chunk size, and crash or hang
Scylla when it runs out of memory. So in this patch we add a hard limit
of 128 KB for the chunk size - anything larger is refused.
Fixes#9933
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes#14267
Fixes https://github.com/scylladb/scylladb/issues/13578
Now that the documentation is versioned, we can remove
the .. versionadded:: and .. versionchanged:: information
(especially that the latter is hard to maintain and now
outdated), as well as the outdated information about
experimental features in very old releases.
This commit removes that information and nothing else.
Closes#13680
The tombstone_gc was documented as experimental in version 5.0.
It is no longer experimental in version 5.2.
This commit updates the information about the option.
Closes#13469
Related: https://github.com/scylladb/scylladb/issues/13119
This commit removes the pages that describe Enterprise only features
from the Open Source documentation:
- Encryption at Rest
- Workload Prioritization
- LDAP Authorization
- LDAP Authentication
- Audit
In addition, it removes most of the information about Incremental
Compaction Strategy (ICS), which is replaced with links to the
Enterprise documentation.
The changes above required additional updates introduced with this
commit:
- The links to Enterprise-only features are replaced with the
corresponding links in the Enterprise documentation.
- The redirections are added for the removed pages to be redirected to
the corresponding pages in the Enterprise documentation.
This commit must be reverted in the scylla-enterprise repository to
avoid deleting the Enterprise-only content from the Enterprise docs.
Closes#13123
