enhancement: the regex consumes an excessive amount of memory.

[zwang28]

Describe the bug

The cluster has 1000+ MVs, where each MV contains a regex. The regex lib holds 70+GB memory consistently.

manual.heap.collapsed.zip

Error message/log

No response

To Reproduce

No response

Expected behavior

No response

How did you deploy RisingWave?

No response

The version of RisingWave

v1.8

backtrack_limit increased from 1_000_000 to 1_000_000_000

Additional context

No response

[BugenZhao]

Each executor within the same operator will create its own expressions, which are usually identical but consume multiple resources. Moreover, if the same expression node is present in different operators or streaming jobs, it can also be reused.

We may consider perform some caching on different granularities:

• cache the results of build_expr based on their protobuf input
• cache the "context"s that are believed to be memory-consuming based on its own input, like RegexpContext in this case

[zwang28]

Pls note that in this cluster I've raised backtrack_limit from 1_000_000 to 1_000_000_000 to work around Error::BacktrackLimitExceeded. So there's indeed very large regex state which requires sizable runtime memory.

Because the memory pool never contracts in size, it may explain the large memory footprint.