roseduan opened a new issue, #1824:
URL: https://github.com/apache/cloudberry/issues/1824
### Apache Cloudberry version
main
### What happened
Cloudberry does not currently support running a `CustomScan` provider
under parallel execution. When `enable_parallel = on` and the plan
tree contains a `CustomScanState`, the CB-specific parallel-execution
walkers either skip CustomScan or wire only a subset of the per-node
parallel hooks, so DSM segment allocation, worker initialisation, and
per-worker state recovery for CustomScan nodes do not behave the same
way as for built-in parallel-aware nodes (SeqScan, IndexScan, etc.).
The upstream-style walkers in `src/backend/executor/execParallel.c`
do handle `T_CustomScanState`, but the **CB-specific** Gp* walkers in
the same file are the ones that drive parallelism inside CB segments,
and the CustomScan branches there are incomplete.
## Functions that need to grow CustomScan support
`src/backend/executor/execParallel.c`:
- `EstimateGpParallelDSMEntrySize()` (line 1548)
- `InitializeGpParallelWorkers()` (line 1622)
- `InitializeGpParallelDSMEntry()` (line 1689)
`src/backend/executor/execProcnode.c`:
- `planstate_walk_kids()`
For reference, the existing parallel-CustomScan hook API in
`src/include/executor/nodeCustom.h` (`ExecCustomScanEstimate`,
`ExecCustomScanInitializeDSM`, `ExecCustomScanReInitializeDSM`,
`ExecCustomScanInitializeWorker`) is what the CB walkers should call;
the upstream walkers in the same file already demonstrate the calling
convention.
## Why this matters
Cloudberry extensions that ship a `CustomScan` provider cannot rely on
parallel-aware execution today.
Tracking this as a single feature-gap issue so a CustomScan
provider in Cloudberry has a single reference point.
### What you think should happen instead
_No response_
### How to reproduce
none
### Operating System
any
### Anything else
_No response_
### Are you willing to submit PR?
- [x] Yes, I am willing to submit a PR!
### Code of Conduct
- [x] I agree to follow this project's [Code of
Conduct](https://github.com/apache/cloudberry/blob/main/CODE_OF_CONDUCT.md).
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