In the following patch we plan to remove the base schema from the base_info
to make the base_info immutable. To do that, we first prepare the schema
registry for the change; we need to be able to create view schemas from
frozen schemas there and frozen schemas have no information about the base
table. Unless we do this change, after base schemas are removed from the
base info, we'll no longer be able to load a view schema to the schema registry
without looking up the base schema in the database.
This change also required some updates to schema building:
* we add a method for unfreezing a view schema with base info instead of
a base schema
* we make it possible to use schema_builder with a base info instead of
a base schema
* we add a method for creating a view schema from mutations with a base info
instead of a base schema
* we add a view_info constructor withat base info instead of a base schema
* we update the naming in schema_registry to reflect the usage of base info
instead of base schema
Currently, the base_info may or may not be set in view schemas.
Even when it's set, it may be modified. This necessitates extra
checks when handling view schemas, as well as potentially causing
errors when we forget to set it at some point.
Instead, we want to make the base info an immutable member of view
schemas (inside view_info). The first step towards that is making
sure that all newly created schemas have the base info set.
We achieve that by requiring a base schema when constructing a view
schema. Unfortunately, this adds complexity each time we're making
a view schema - we need to get the base schema as well.
In most cases, the base schema is already available. The most
problematic scenario is when we create a schema from mutations:
- when parsing system tables we can get the schema from the
database, as regular tables are parsed before views
- when loading a view schema using the schema loader tool, we need
to load the base additionally to the view schema, effectively
doubling the work
- when pulling the schema from another node - in this case we can
only get the current version of the base schema from the local
database
Additionally, we need to consider the base schema version - when
we generate view updates the version of the base schema used for
reads should match the version of the base schema in view's base
info.
This is achieved by selecting the correct (old or new) schema in
`db::schema_tables::merge_tables_and_views` and using the stored
base schema in the schema_registry.
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>
Currently, if version is missing, we use a unique timeuuid as the
version. It's not useful for creating static schema of system tables
because to achieve the same version on all the nodes, version needs to
be provided externally.
This patch introduces a way to build the schema with version computed
from schema definition, so we can have a stable version which is the
same on all machines.
Will be used for reliable computation of schema version for system
tables. System tables currently set the version statically and we rely
on the developer to bump up the version manually when the definition
changes. We cannot use mutation hash, since system tables are
initialized too rearly (mutation hash needs system schema to be
already there). This is a very error prone process, as it is easy to
forget to do so, and the issue comes up only when testing mixed
clusters.
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 the properties via DDL, Cassandra would fails to consume
the CQL statement to 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 this is 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>
The schema_builder::build() method creates a copy of raw schema
internaly in a hope that builder will be updated and be asked to build
the resulting schema again (e.g. alternator uses this).
However, there are places that build schema using temporary object once
in a `return schema_builder().with_...().build()` manner. For those
invocations copying raw schema is just waste of cycles.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
Closesscylladb/scylladb#18094
This patch continues the refactoring, now we move
wait_for_sync_to_commitlog property from schema_builder to
schema_static_props.
The patch replaces schema_builder::set_wait_for_sync_to_commitlog
and is_extra_durable with two register_static_configurator,
one in system_keyspace and another in system_distributed_keyspace.
They correspond to the two parts of the original disjunction
in schema_tables::is_extra_durable.
Our goal (#12642) is to mark raft tables to use
schema commitlog. There are two similar
cases in code right now - with_null_sharder
and set_wait_for_sync_to_commitlog schema_builder
methods. The problem is that if we need to
mark some new schema with one of these methods
we need to do this twice - first in
a method describing the schema
(e.g. system_keyspace::raft()) and second in the
function create_table_from_mutations, which is not
obvious and easy to forget.
create_table_from_mutations is called when schema object
is reconstructed from mutations, with_null_sharder
and set_wait_for_sync_to_commitlog must be called from it
since the schema properties they describe are
not included in the mutation representation of the schema.
This patch proposes to distinguish between the schema
properties that get into mutations and those that do not.
The former are described with schema_builder, while for
the latter we introduce schema_static_props struct and
the schema_builder::register_static_configurator method.
This way we can formulate a rule once in the code about
which schemas should have a null sharder, and it will
be enforced in all cases.
Schema related files are moved there. This excludes schema files that
also interact with mutations, because the mutation module depends on
the schema. Those files will have to go into a separate module.
Closes#12858
