in hope to lower the bar to testing object store.
* add language specifier for better readability of the document.
to highlight the config with YAML syntax
* add more specific comment on the AWS related settings
* explain that endpoint should match in the CREATE KEYSPACE
statement and the one defined by the YAML configuration.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#15433
Load balancer will recognize decommissioning nodes and will
move tablet replicas away from such nodes with highest priority.
Topology changes have now an extra step called "tablet draining" which
calls the load balancer. The step will execute tablet migration track
as long as there are nodes which require draining. It will not do regular
load balancing.
If load balancer is unable to find new tablet replicas, because RF
cannot be met or availability is at risk due to insufficient node
distribution in racks, it will throw an exception. Currently, topology
change will retry in a loop. We should make this error cause topology
change to be aborted. There is no infrastructure for
aborts yet, so this is not implemented.
Closes#15197
* github.com:scylladb/scylladb:
tablets, raft topology: Add support for decommission with tablets
tablet_allocator: Compute load sketch lazily
tablet_allocator: Set node id correctly
tablet_allocator: Make migration_plan a class
tablets: Implement cleanup step
storage_service, tablets: Prevent stale RPCs from running beyond their stage
locator: Introduce tablet_metadata_guard
locator, replica: Add a way to wait for table's effective_replication_map change
storage_service, tablets: Extract do_tablet_operation() from stream_tablet()
raft topology: Add break in the final case clause
raft topology: Fix SIGSEGV when trace-level logging is enabled
raft topology: Set node state in topology
raft topology: Always set host id in topology
Load balancer will recognize decommissioning nodes and will
move tablet replicas away from such nodes with highest priority.
Topology changes have now an extra step called "tablet draining" which
calls the load balancer. The step will execute tablet migration track
as long as there are nodes which require draining. It will not do regular
load balancing.
If load balancer is unable to find new tablet replicas, because RF
cannot be met or availability is at risk due to insufficient node
distribution in racks, it will throw an exception. Currently, topology
change will retry in a loop. We should make this error cause topology
change to be paused so that admin becomes aware of the problem and
issues an abort on the topology change. There is no infrastructure for
aborts yet, so this is not implemented.
we get the path object storage config like:
```c++
db::config::get_conf_sub("object_storage.yaml").native()
```
so, the default path should be $SCYLLA_CONF/object_storage.yaml.
in this change, it is corrected.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#15406
We change the type of IDs in CDC_GENERATIONS_V3 to timeuuid to
give them a time-based order. We also change how we initialize
them so that the new CDC generation always has the highest ID.
This is the last step to enabling the efficient clearing of
obsolete CDC generation data.
Additionally, we change the types of current_cdc_generation_uuid,
new_cdc_generation_data_uuid and the second values of the elements
in unpublished_cdc_generations to timeuuid, so that they match id
in CDC_GENERATIONS_V3.
After moving the creation of uuid out of
make_new_generation_description, this function only calls the
topology_description_generator's constructor and its generate
method. We could remove this function, but we instead simplify
the code by removing the topology_description_generator class.
We can do this refactor because make_new_generation_description
is the only place using it. We inline its generate method into
make_new_generation_description and turn its private methods into
static functions.
We make CDC_GENERATIONS_V3 single-partition by adding the key
column and changing the clustering key from range_end to
(id, range_end). This is the first step to enabling the efficient
clearing of obsolete CDC generation data, which we need to prevent
Raft-topology snapshots from endlessly growing as we introduce new
generations over time. The next step is to change the type of the id
column to timeuuid. We do it in the following commits.
After making CDC_GENERATIONS_V3 single-partition, there is no easy
way of preserving the num_ranges column. As it is used only for
sanity checking, we remove it to simplify the implementation.
In the following commits, we replace the
topology::transition_state::publish_cdc_generation state with
a background fiber that continually publishes committed CDC
generations. To make these generations accessible to the
topology coordinator, we store them in the new column of
system.topology -- unpublished_cdc_generations.
Add a document describing in detail how to use clang's "-ftime-trace"
option, and the ClangBuildAnalyzer tool, to find the source files,
header files and templates which slow down Scylla's build the most.
I've used this tool in the past to reduce Scylla build time - see
commits:
fa7a302130 (reduced 6.5%)
f84094320d (reduced 0.1%)
6ebf32f4d7 (reduced 1%)
d01e1a774b (reduced 4%)
I'm hoping that documenting how to use this tool will allow other
developers to suggest similar commits.
Refs #1.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Closes#15209
We add support for `--ignore-dead-nodes` in `raft_removenode` and
`--ignore-dead-nodes-for-replace` in `raft_replace`. For now, we allow
passing only host ids of the ignored nodes. Supporting IPs is currently
impossible because `raft_address_map` doesn't provide a mapping from IP
to a host id.
The main steps of the implementation are as follows:
- add the `ignore_nodes` column to `system.topology`,
- set the `ignore_nodes` value of the topology mutation in `raft_removenode` and `raft_replace`,
- extend `service::request_param` with alternative types that allow storing a set of ids of the ignored nodes,
- load `ignore_nodes` from `system.topology` into `request_param` in `system_keyspace::load_topology_state`,
- add `ignore_nodes` to `exclude_nodes` in `topology_coordinator::exec_global_command`,
- pass `ignore_nodes` to `replace_with_repair` and `remove_with_repair` in `storage_service::raft_topology_cmd_handler`.
Additionally, we add `test_raft_ignore_nodes.py` with two tests that verify the added changes.
Fixes#15025Closes#15113
* github.com:scylladb/scylladb:
test: add test_raft_ignore_nodes
test: ManagerClient.remove_node: allow List[HostId] for ignore_dead
raft topology: pass ignore_nodes to {replace, remove}_with_repair
raft topology: exec_global_command: add ignore_nodes to exclude_nodes
raft topology: exec_global_command: change type of exclude_nodes
topology_state_machine: extend request_param with a set of raft ids
raft topology: set ignore_nodes in raft_removenode and raft_replace
utils: introduce split_comma_separated_list
raft topology: add the ignore_nodes column to system.topology
In the following commits, we add support for --ignore-dead-nodes
in raft_removenode and --ignore-dead-nodes-for-replace in
raft_replace. To make these request parameters accessible for the
topology coordinator, we store them in the new ignore_nodes
column of system.topology.
The system.tablets table stores replica sets as a CQL set type,
which is sorted. This means that if, in a tablet replica set
[n1, n2, n3] n2 is replaced with n4, then on reload we'll see
[n1, n3, n4], changing the relative position of n3 from the third
replica to the second.
The relative position of replicas in a replica set is important
for materialized views, as they use it to pair base replicas with
view replicas. To prepare for materialized views using tablets,
change the persistent data type to list, which preserves order.
The code that generates new replica sets already preserves order:
see locator::replace_replica().
While this changes the system schema, tablets are an experimental
feature so we don't need to worry about upgrades.
Closes#15111
After this change, the load balancer can make progress with active
migrations. If the algorithm is called with active tablet migrations
in tablet metadata, those are treated by load balancer as if they were
already completed. This allows the algorithm to incrementally make
decision which when executed with active migrations will produce the
desired result.
Overload of shards is limited by the fact that the algorithm tracks
streaming concurrency on both source and target shards of active
migrations and takes concurrency limit into account when producing new
migrations.
The coordinator executes the load balancer on edges of tablet state
machine stransitions. This allows new migrations to be started as soon
as tablets finish streaming.
The load balancer is also continuously invoked as long as it produces
a non-empty plan. This is in order to saturate the cluster with
streaming. A single make_plan() call is still not saturating, due
to the way algorithm is implemented.
and add docs/dev/timestamp-conflict-resolution.md
to document the details of the conflict resolution algorithm.
Refs scylladb/scylladb#14063
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Containing two tables, describing all the possible operations seen in user, system and streaming semaphore diagnostics dumps.
Closes#14171
* github.com:scylladb/scylladb:
docs/dev/reader-concurrency-semaphore.md: add section about operations
docs/dev/reader-concurrency-semaphore.md: switch to # headers markings
reader_concurrency_semaphore: s/description/operation/ in diagnostics dumps
* indent the nested paragraphs of list items
* use table to format the time sequence for better
readability
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#14016
not all tables in system keyspace are volatile. among other things,
system.sstables and system.tablets are persisted using sstables like
regular user tables. so move them into the section where we have
other regular tables there.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
we changed the type of generation column in system.sstables
from bigint to timeuuid in 74e9e6dd1a
but that change failed to update the document accordingly. so let's
update the document to reflect the change.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes#13994
`check_and_repair_cdc_streams` is an existing API which you can use when the
current CDC generation is suboptimal, e.g. after you decommissioned a node the
current generation has more stream IDs than you need. In that case you can do
`nodetool checkAndRepairCdcStreams` to create a new generation with fewer
streams.
It also works when you change number of shards on some node. We don't
automatically introduce a new generation in that case but you can use
`checkAndRepairCdcStreams` to create a new generation with restored
shard-colocation.
This PR implements the API on top of raft topology, it was originally
implemented using gossiper. It uses the `commit_cdc_generation` topology
transition state and a new `publish_cdc_generation` state to create new CDC
generations in a cluster without any nodes changing their `node_state`s in the
process.
Closes#13683
* github.com:scylladb/scylladb:
docs: update topology-over-raft.md
test: topology_experimental_raft: test `check_and_repair_cdc` API
raft topology: implement `check_and_repair_cdc_streams` API
raft topology: implement global request handling
raft topology: introduce `prepare_new_cdc_generation_data`
raft_topology: `get_node_to_work_on_opt`: return guard if no node found
raft topology: remove `node_to_work_on` from `commit_cdc_generation` transition
raft topology: separate `publish_cdc_generation` state
raft topology: non-node-specific `exec_global_command`
raft topology: introduce `start_operation()`
raft topology: non-node-specific `topology_mutation_builder`
topology_state_machine: introduce `global_topology_request`
topology_state_machine: use `uint16_t` for `enum_class`es
raft topology: make `new_cdc_generation_data_uuid` topology-global
It was already outdated before this PR.
Describe the version of topology state machine implemented in this PR.
Fix some typos and make it proper markdown so it renders nicely on
GitHub etc.
Update the `Generation switching` section: most of the existing
description landed in `Gossiper-based topology changes` subsection, and
a new subsection was added to describe Raft group 0 based topology
changes. Marked as WIP - we expect further development in this area
soon.
The existing gossiper-based description was also updated a bit.
Greatly expand on the details of how the semaphore works.
Organize the content into thematic chapters to improve navigation.
Improve formatting while at it.
The names of these states have been the source of confusion ever since
they were introduced. Give them names which better reflects their true
meaning and gives less room for misinterpretation. The changes are:
* active/unused -> active
* active/used -> active/need_cpu
* active/blocked -> active/await
Hopefully the new names do a better job at conveying what these states
really mean:
* active - a regular admitted permit, which is active (as opposed to
an inactive permit).
* active/need_cpu - an active permit which was marked as needing CPU for
the read to make progress. This permit prevents admission of new
permits while it is in this state.
* active/await - a former active/need_cpu permit, which has to wait on
I/O or a remote shard. While in this state, it doesn't block the
admission of new permits (pending other criteria such as resource
availability).
The schema is
CREATE TABLE system.sstables (
location text,
generation bigint,
format text,
status text,
uuid uuid,
version text,
PRIMARY KEY (location, generation)
)
A sample entry looks like:
location | generation | format | status | uuid | version
---------------------------------------------------------------------+------------+--------+--------+--------------------------------------+---------
/data/object_storage_ks/test_table-d096a1e0ad3811ed85b539b6b0998182 | 2 | big | sealed | d0a743b0-ad38-11ed-85b5-39b6b0998182 | me
The uuid field points to the "folder" on the storage where the sstable
components are. Like this:
s3
`- test_bucket
`- f7548f00-a64d-11ed-865a-0c1fbc116bb3
`- Data.db
- Index.db
- Filter.db
- ...
It's not very nice that the whole /var/lib/... path is in fact used as
location, it needs the PR #12707 to fix this place.
Also, the "status" part is not yet fully functional, it only supports
three options:
- creating -- the same as TemporaryTOC file exists on disk
- sealed -- default state
- deleting -- the analogy for the deletion log on disk
The latter needs support from the distributed_loader, which's not yet
there. In fact, distributes_loader also needs to be patched to actualy
select entries from this table on load. Also it needs the mentioned
PR #12707 to support staging and quarantine sstables.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
The topology state machine will track all the nodes in a cluster,
their state, properties (topology, tokens, etc) and requested actions.
Node state can be one of those:
none - the node is not yet in the cluster
bootstrapping - the node is currently bootstrapping
decommissioning - the node is being decommissioned
removing - the node is being removed
replacing - the node is replacing another node
normal - the node is working normally
rebuild - the node is being rebuilt
left - the node is left the cluster
Nodes in state left are never removed from the state.
Tokens also can be in one of the states:
write_both_read_old - writes are going to new and old replica, but reads are from
old replicas still
write_both_read_new - writes still going to old and new replicas but reads are
from new replica
owner - tokens are owned by the node and reads and write go to new
replica set only
Tokens that needs to be move start in 'write_both_read_old' state. After entire
cluster learns about it streaming start. After the streaming tokens move
to 'write_both_read_new' state and again the whole cluster needs to learn about it
and make sure no reads started before that point exist in the system.
After that tokens may move to 'owner' state.
topology_request is the field through which a topology operation request
can be issued to a node. A request is one of the topology operation
currently supported: join, leave, replace or remove.
Until now, the instructions on generating wasm files and using them
for Scylla UDFs were stored in docs/dev, so they were not visible
on the docs website. Now that the Rust helper library for UDFs
is ready, and we're inviting users to try it out, we should also
make the rest of the Wasm UDF documentation readily available
for the users.
Closes#13139
When the WASM UDFs were first introduced, the LANGUAGE required in
the CQL statements to use them was "xwasm", because the ABI for the
UDFs was still not specified and changes to it could be backwards
incompatible.
Now, the ABI is stabilized, but if backwards incompatible changes
are made in the future, we will add a new ABI version for them, so
the name "xwasm" is no longer needed and we can finally
change it to "wasm".
Closes#13089
The WASM UDF implementation has changed since the last time the docs
were written. In particular, the Rust helper library has been
released, and using it should be the recommended method.
Some decisions that were only experimental at the start, were also
"set in stone", so we should refer to them as such.
The docs also contain some code examples. This patch adds tests for
these examples to make sure that they are not wrong and misleading.
Closes#12941
