Feature: add pg_query_state to gp_stats_collector

[roaldm153]

What does this PR do?

Adds a signal-based runtime query-state facility to the gp_stats_collector extension. It lets a session inspect the live execution state of another running backend on demand - walking its active plan tree across the QD and all QEs - without waiting for the query to finish, pushing batches to the UDS(unix domain socket).

New SQL API (extension v1.2, schema gpsc):

• gpsc.pg_query_state(pid, trace_id) - fan out a poll to the query running on pid; each participating backend walks its plan tree and logs a per-node snapshot.
• gpsc.pg_query_state_backends(pid) - list the (segid, pid) QE backends taking part in that query.
• cbdb_mpp_query_state(gpsc.gp_segment_pid[], trace_id) - QE-side dispatch target.

The extension embeds the pg_query_state signal layer, which depends on three PostgreSQL core changes folded directly into the tree (configure enables the extension by default, so the tree must build without a manual patch step):

• custom ProcSignal handlers (procsignal.c/.h, postgres.c);
• end-of-node instrumentation flag readable mid-run (instrument.c/.h);
• runtime EXPLAIN entry points (explain.c/.h).

Type of Change

• Bug fix (non-breaking change)
• New feature (non-breaking change)
• Breaking change (fix or feature with breaking changes)
• Documentation update

Breaking Changes

None. Core changes are additive (new signal reasons, a new Instrumentation field, new runtime-EXPLAIN paths); existing behavior is unchanged.

Test Plan

• Unit tests added/updated

• Integration tests added/updated

• Passed make installcheck

• pg_regress (gpcontrib/gp_stats_collector/test): catalog contract (function/type registration, exec location) and input-validation errors.

• isolation2 (gpcontrib/gp_stats_collector/test/isolation2), multi-session:

  • gpsc_pqs_backends - idle backend yields an empty list;
  • gpsc_pqs_running - happy path: poll a query suspended on the QEs via a fault injector;
  • gpsc_pqs_perms - permission gate (non-owner non-superuser denied);
  • gpsc_pqs_disabled - STAT_DISABLED reports no backends;
  • gpsc_pqs_seg_count - one backend per primary segment.

• gpsc-crash-test - parallel tracing on make installcheck-parallel, core dumps checking

• A dedicated CI workflow builds Cloudberry with the extension across ubuntu22.04/rocky8/rocky9 and runs the pg_regress, isolation2, and core regression suites.

Impact

Performance:
No steady-state cost. Work happens only when a poll is issued: one signal fan-out plus a bounded shared-memory round-trip; the shmem lock is held only around the request, not during dispatch.

User-facing changes:
New gpsc.pg_query_state* functions and the pg_query_state.enable GUC. Functions are granted to PUBLIC; access is gated in C so a caller may poll a backend only if it is a superuser or owns the target query.

Dependencies:
None.

Checklist

• Followed contribution guide
• Added/updated documentation
• Reviewed code for security implications
• Requested review from cloudberry committers

Additional Context

The signal layer under src/pg_query_state/ is derived from pg_query_state (PostgreSQL License). Derived files carry dual license headers (ASF + Portions Copyright Postgres Professional) and the root LICENSE records a PostgreSQL-License notice for it. Happy to provide provenance details for IP clearance.