use utils::chunked_vector instead of std::vector to store cdc stream
sets for tablets.
a cdc stream set usually represents all streams for a specific table and
timestamp, and has a stream id per each tablet of the table. each stream
id is represented by 16 bytes. thus the vector could require quite large
contiguous allocations for a table that has many tablets. change it to
chunked_vector to avoid large contiguous allocations.
Fixesscylladb/scylladb#26791Closesscylladb/scylladb#26792
when loading CDC streams metadata for tablets from the tables, read only
new entries from the history table instead of reading all entries. This
improves the CDC metadata reloading, making it more efficient and
predictable.
the CDC metadata is loaded as part of group0 reload whenever the
internal CDC tables are modified. on tablet split / merge, we create a
new CDC timestamp and streams by writing them to the cdc_streams_history
table by group0 operation, and when it's applied we reload the in-memory
CDC streams map by reading from the tables and constructing the updated map.
Previously, on every update, we would read the entire
cdc_streams_history entries for the changed table, constructing all its
streams and creating a new map from scratch.
We improve this now by reading only new entries from cdc_streams_history
and append them to the existing map. we can do this because we only
append new entries to cdc_streams_history with higher timestamp than all
previous entries.
This makes this reloading more efficient and predictable, because
previously we would read a number of entries that depends on the number
of tablets splits and merges, which increases over time and is
unbounded, whereas now we read only a single stream set on each update.
Fixesscylladb/scylladb#26732
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
When choosing a CDC stream to generate CDC log writes to, if the
keyspace uses tablets, we need to choose a stream according to the
relevant metadata which is specific to tablets-enabled keyspaces.
We define the method get_tablet_stream that given a table, write
timestamp, and token, returns the stream that the log entry should
be written to.
The method works by looking up the stream metadata of the table, then
finding the relevant stream set by timestamp, and finally finding
the stream that covers the token range that contains the token.
the get_stream method is relevant only for vnode-based keyspaces. next
we will introduce a new method to get a stream in a tablets-based
keyspace. prepare for this by renaming get_stream to get_vnode_stream.
Read the CDC stream metadata from the internal system tables, and store
it in the cdc metadata data structures.
The metadata is stored in the tables as diffs which is more storage
efficient, but when in-memory we store it as full stream sets for each
timestamp. This is more useful because we need to be able to find a
stream given timestamp and token.
Before this patch, writes to the previous CDC generations would
always be rejected. After this patch, they will be accepted if
the write's timestamp is greater than `now - generation_leeway`.
This change was proposed around 3 years ago. The motivation was
to improve user experience. If a client generates timestamps by
itself and its clock is desynchronized with the clock of the node
the client is connected to, there could be a period during
generation switching when writes fail. We didn't consider this
problem critical because the client could simply retry a failed
write with a higher timestamp. Eventually, it would succeed. This
approach is safe because these failed writes cannot have any side
effects. However, it can be inconvenient. Writing to previous
generations was proposed to improve it.
The idea was rejected 3 years ago. Recently, it turned out that
there is a case when the client cannot retry a write with the
increased timestamp. It happens when a table uses CDC and LWT,
which makes timestamps permanent. Once Paxos commits an entry with
a given timestamp, Scylla will keep trying to apply that entry
until it succeeds, with the same timestamp. Applying the entry
involves writing to the CDC log table. If it fails, we get stuck.
It's a major bug with an unknown perfect solution.
Allowing writes to previous generations for `generation_leeway` is
a probabilistic fix that should solve the problem in practice.
Note that allowing writes only to the previous generation might
not be enough. With the Raft-based topology, it is possible to
add multiple nodes concurrently. Moreover, tablets make streaming
instant, which allows the topology coordinator to add multiple nodes
very quickly. So, creating generations with almost identical
timestamps is possible. Then, we could encounter the same bug but,
for example, for a generation before the previous generation.
Fixes some typos as found by codespell run on the code.
In this commit, I was hoping to fix only comments, not user-visible alerts, output, etc.
Follow-up commits will take care of them.
Refs: https://github.com/scylladb/scylladb/issues/16255
Signed-off-by: Yaniv Kaul <yaniv.kaul@scylladb.com>
Instead of lengthy blurbs, switch to single-line, machine-readable
standardized (https://spdx.dev) license identifiers. The Linux kernel
switched long ago, so there is strong precedent.
Three cases are handled: AGPL-only, Apache-only, and dual licensed.
For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0),
reasoning that our changes are extensive enough to apply our license.
The changes we applied mechanically with a script, except to
licenses/README.md.
Closes#9937
Refs #6864
When booting a clean scylla, CDC stream ID:s will not be availble until
a n*ring delay time period has passed. Before this, writing to a CDC
enabled table will fail hard.
For alternator (and its tests), we can report the stream(s) for tables as not yet
available (ENABLING) until such time as id:s are
computed.
v2:
* Keep storage service ref in executor
Since token representation is fixed now, all the partitioners
will share the sharding logic. It makes sense now to keep
the logic in common super class and separate header that's
included only in i_partitioner.cc.
shard_of and token_for_next_shard are now implemented in
i_partitioner. They would be non-virtual but we have to
keep them virtual because one test is overriding them
to enforce some specific sharding.
Signed-off-by: Piotr Jastrzebski <piotr@scylladb.com>
The class stores a queue of CDC generations to be used for choosing
streams when writing to the CDC log.
This data structure will be updated on some gossip events (when a new node
joins the cluster and proposes a new generation of CDC streams).
