Module mz_adapter::coord
source · Expand description
Translation of SQL commands into timestamped Controller
commands.
The various SQL commands instruct the system to take actions that are not yet explicitly timestamped. On the other hand, the underlying data continually change as time moves forward. On the third hand, we greatly benefit from the information that some times are no longer of interest, so that we may compact the representation of the continually changing collections.
The Coordinator
curates these interactions by observing the progress
collections make through time, choosing timestamps for its own commands,
and eventually communicating that certain times have irretrievably “passed”.
§Frontiers another way
If the above description of frontiers left you with questions, this repackaged explanation might help.
-
since
is the least recent time (i.e. oldest time) that you can read from sources and be guaranteed that the returned data is accurate as of that time.Reads at times less than
since
may return values that were not actually seen at the specified time, but arrived later (i.e. the results are compacted).For correctness’ sake, the coordinator never chooses to read at a time less than an arrangement’s
since
. -
upper
is the first time after the most recent time that you can read from sources and receive an immediate response. Alternately, it is the least time at which the data may still change (that is the reason we may not be able to respond immediately).Reads at times >=
upper
may not immediately return because the answer isn’t known yet. However, once theupper
is > the specified read time, the read can return.For the sake of returned values’ freshness, the coordinator prefers performing reads at an arrangement’s
upper
. However, because we more strongly prefer correctness, the coordinator will choose timestamps greater than an object’supper
if it is also being accessed alongside objects whosesince
times are >= itsupper
.
This illustration attempts to show, with time moving left to right, the
relationship between since
and upper
.
#
: possibly inaccurate results-
: immediate, correct response?
: not yet knowns
: sinceu
: upper|
: eligible for coordinator to select
####s----u?????
|||||||||||
Modules§
- appends 🔒Logic and types for all appends executed by the
Coordinator
. - Special cases related to the “catalog serving” of Materialize
- Internal consistency checks that validate invariants of
Coordinator
. - ddl 🔒This module encapsulates all of the
Coordinator
’s logic for creating, dropping, and altering objects. - A timestamp oracle that relies on the
crate::catalog::Catalog
for persistence/durability and reserves ranges of timestamps. - indexes 🔒
- Support for unified compute introspection.
- Logic for processing
Coordinator
messages. TheCoordinator
receives messages from various sources (ex: controller, clients, background tasks, etc). - peek 🔒Logic and types for creating, executing, and tracking peeks.
- Types and methods related to initializing, updating, and removing read policies on collections.
- Logic for executing a planned SQL query.
- sql 🔒Various utility methods used by the
Coordinator
. Ideally these are all put in more meaningfully named modules. - timeline 🔒A mechanism to ensure that a sequence of writes and reads proceed correctly through timestamps.
- Logic for selecting timestamps for various operations on collections.
- validity 🔒
Structs§
- Configures a coordinator.
- Metadata about an active connection.
- Glues the external world to the Timely workers.
- Bundle of state related to statement execution.
- State that the coordinator must process as part of retiring command execution.
ExecuteContextExtra::Default
is guaranteed to produce a value that will cause the coordinator to do nothing, and is intended for use by code that invokes the execution processing flow (i.e.,sequence_plan
) without actually being a statement execution. - Context needed to check the hydration status of clusters.
- Contains information about the last message the
Coordinator
processed. - A struct for tracking the ownership of a lock and a VecDeque to store to-be-done work after the lock is freed.
- A pending read transaction waiting to be linearized along with metadata about it’s state
- A pending transaction waiting to be committed.
- Soft-state metadata about a compute replica
Enums§
- A pending read transaction waiting to be linearized.
- The response we’ll send for a
PendingTxn
. - Result types for each stage of a sequence.
- An enum describing which cluster to run a statement on.
Traits§
- Staged 🔒Common functionality for Coordinator::sequence_staged.
Functions§
- Serves the coordinator based on the provided configuration.