[BACKPORT 2025.1][#31870] DocDB: PgResponseCache entries become invalid after the originating RPC's deadline

[kai-franz]

DO NOT MERGE!! CSI ⏳

Summary:
PgResponseCache::Data::IsValid unconditionally checked
now < readiness_deadline_, where readiness_deadline_ is set once at
entry creation from the originating RPC's wall-clock deadline (the YSQL
client RW timeout, ~10 min by default). This caused every cache entry --
even one with a successful, populated, version-current response --
to become "invalid" once wall-clock crossed that deadline, forcing a
full rebuild every few minutes. The rebuilt RPC's response carries a fresh
catalog_read_time that propagates into subsequent paged RPCs' cache
keys, so one expiry cascades into ~5 misses per preload sequence on
every new connection's prefetch.

This was a regression introduced by #27412 (commit f960a4a, "Async
wait on pg response cache"). Pre-refactor, the deadline was only
consulted while the response was still in-flight:

return version == version_ &&
(IsReady(future_) ? IsOk(future_.get()) : now < readiness_deadline_);

Restore the pre-refactor semantics: the deadline remains a watchdog on
a stalled fetch, but a populated successful response stays valid until
catalog-version invalidation or LRU eviction supersedes it. The same
change was reverted on the 2024.2.4 backport branch (commit
413142a); this fix restores correct behavior on master.

Original commit: 36b344f / D53645

Test Plan:
New test:
./yb_build.sh release --cxx-test pg_catalog_perf-test
--gtest_filter PgCatalogPerfTest.ResponseCacheValidPastReadinessDeadline

Regression check (all response-cache tests):
./yb_build.sh release --cxx-test pg_catalog_perf-test
--gtest_filter 'ResponseCache'

Verified locally that:

• The new test fails before the IsValid fix (cache.hits = 0 instead of 5)
  when the warm-up entry's readiness_deadline has elapsed.
• The new test passes with the fix.
• All 10 existing ResponseCache tests still pass.

Reviewers: dmitry

Reviewed By: dmitry

Subscribers: svc_phabricator, yql, ybase

Differential Revision: https://phorge.dev.yugabyte.com/D53645

[gemini-code-assist]

Code Review

This pull request refactors the response cache in pg_response_cache.cc by replacing the failed_ boolean flag with a DataState enum (kNotReady, kReadyOK, kReadyFailure). This allows the cache to remain valid and usable even after the readiness deadline has passed, provided the data has been successfully loaded (kReadyOK). A new integration test ResponseCacheValidPastReadinessDeadline has been added to verify this behavior under short RPC deadlines. I have no feedback to provide as the changes look correct and are well-tested.

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[kai-franz]

Trigger Jenkins

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[yb-agentk-dev]

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