Module mz_join_core

A fork of DD’s JoinCore::join_core.

Currently, compute rendering knows two implementations for linear joins:

• Differential’s JoinCore::join_core
• A Materialize fork thereof, called mz_join_core
• Another Materialize fork thereof, called mz_join_core_v2

mz_join_core exists to solve a responsiveness problem with the DD implementation. DD’s join is only able to yield between keys. When computing a large cross-join or a highly skewed join, this can result in loss of interactivity when the join operator refuses to yield control for multiple seconds or longer, which in turn causes degraded user experience.

mz_join_core currently fixes the yielding issue by omitting the linear scan through times implemented in DD’s join implementation. This leaves only the quadratic strategy for which it is easy to implement yielding within keys.

While mz_join_core retains responsiveness in the face of cross-joins it is also significantly slower than DD’s join for workloads that have a large amount of edits at different times. mz_join_core_v2 resolves this by adding support for the DD join’s linear scan through times.

For the moment, we keep all three implementations around, selectable through feature flags. Eventually, we hope that mz_join_core_v2 proves itself sufficiently to become the only join implementation.

Structs

Deferred 🔒

Deferred join computation.

Functions

mz_join_core 🔒

Joins two arranged collections with the same key type.