git.stella-ops.org/docs/workflow/engine/13-backend-comparison-2026-03-17.md

Backend Comparison 2026-03-17

Purpose

This document compares the current Oracle, PostgreSQL, and MongoDB workflow-engine backends using the published normalized performance baselines and the currently implemented backend-specific validation suites.

This is a decision pack for the current local Docker benchmark set. It is not the final production recommendation pack yet, because hostile-condition and Bulstrad hardening depth is still strongest on Oracle.

The durable machine-readable companion is 13-backend-comparison-2026-03-17.json.

For the exact six-profile signal-driver matrix, including Oracle+Redis, PostgreSQL+Redis, and Mongo+Redis, see 14-signal-driver-backend-matrix-2026-03-17.md.

Source Baselines

• 10-oracle-performance-baseline-2026-03-17.md
• 11-postgres-performance-baseline-2026-03-17.md
• 12-mongo-performance-baseline-2026-03-17.md

Validation Status

Current comparison-relevant validation state:

• Oracle performance suite: 12/12 passed
• PostgreSQL performance suite: 11/11 passed
• MongoDB performance suite: 14/14 passed
• PostgreSQL focused backend parity suite: 9/9 passed
• MongoDB focused backend parity suite: 23/23 passed
• integration project build: 0 warnings, 0 errors

Important caveat:

• Oracle still has the broadest hostile-condition and Bulstrad E2E matrix.
• PostgreSQL and MongoDB now have backend-native signal/runtime/projection/performance coverage plus curated Bulstrad parity, but they do not yet match Oracle's full reliability surface.

Normalized Comparison

Synthetic Signal Round-Trip

Metric	Oracle	PostgreSQL	MongoDB
Serial latency avg ms	3104.85	3079.33	97.88
Serial latency P95 ms	3165.04	3094.94	149.20
Throughput ops/s	20.98	25.74	76.28
Throughput avg ms	4142.13	3603.54	1110.94
Throughput P95 ms	4215.64	3635.59	1121.22
Soak ops/s	3.91	4.30	47.62
Soak avg ms	4494.29	4164.52	322.40
Soak P95 ms	5589.33	4208.42	550.50

Capacity Ladder

Concurrency	Oracle ops/s	PostgreSQL ops/s	MongoDB ops/s
c1	3.37	4.11	7.08
c4	15.22	17.29	38.35
c8	21.34	33.21	66.04
c16	34.03	57.04	68.65

Transport Baselines

Scenario	Oracle ops/s	PostgreSQL ops/s	MongoDB ops/s
Immediate burst nightly	50.18	70.10	46.18
Delayed burst nightly	10.71	19.60	16.66
Immediate burst smoke	56.94	70.21	32.11
Delayed burst smoke	2.86	5.59	4.97

Bulstrad Workloads

Scenario	Oracle ops/s	PostgreSQL ops/s	MongoDB ops/s
QuoteOrAplCancel smoke	19.69	59.88	23.48
QuotationConfirm -> ConvertToPolicy nightly	1.77	3.33	10.83

Backend-Specific Observations

Oracle

• Strongest validation depth and strongest correctness story.
• Main cost center is still commit pressure.
• Dominant wait is log file sync in almost every measured scenario.
• c8 is still the last comfortable rung on the local Oracle Free setup.

PostgreSQL

• Best relational performance profile in the current measurements.
• Immediate transport is the strongest of the three measured backends.
• Dominant wait is Client:ClientRead, which points to queue-claim cadence and short-transaction wake behavior, not a clear storage stall.
• c16 still scales cleanly on this benchmark set and does not yet show a hard saturation cliff.

MongoDB

• Fastest measured backend across the synthetic signal round-trip workloads and the medium Bulstrad nightly flow.
• No stable top wait dominated the measured runs; current analysis is more meaningful through normalized metrics and Mongo counters than through wait classification.
• The significant findings were correctness issues discovered and fixed during perf work:
  • bounded empty-queue receive
  • explicit collection bootstrap before transactional concurrency
• c16 is the first rung where latency visibly expands even though throughput still rises.

Decision View

Raw Performance Ranking

For the current local benchmark set:

1. MongoDB
2. PostgreSQL
3. Oracle

This order is stable for:

• serial latency
• steady-state synthetic throughput
• soak throughput
• medium Bulstrad nightly flow

Validation Maturity Ranking

For the current implementation state:

1. Oracle
2. PostgreSQL
3. MongoDB

Reason:

• Oracle has the deepest hostile-condition and Bulstrad E2E surface.
• PostgreSQL now has a solid backend-native suite and competitive performance, but less reliability breadth than Oracle.
• MongoDB now has good backend-native and performance coverage, but its operational model is still the most infrastructure-sensitive because it depends on replica-set transactions plus change-stream wake behavior.

Current Recommendation

If the next backend after Oracle must be chosen today:

• choose PostgreSQL as the next default portability target

Reason:

• it materially outperforms Oracle on the normalized workflow workloads
• it preserves the relational operational model for runtime state and projections
• its wake-hint model is simpler to reason about operationally than MongoDB change streams
• it now has enough backend-native correctness and Bulstrad parity coverage to be a credible second backend

If the decision is based only on benchmark speed:

• MongoDB is currently fastest

But that is not the same as the safest operational recommendation yet.

What Remains Before A Final Production Recommendation

• expand PostgreSQL hostile-condition coverage to match the broader Oracle matrix
• expand MongoDB hostile-condition coverage to match the broader Oracle matrix
• widen the curated Bulstrad parity pack further on PostgreSQL and MongoDB
• rerun the shared parity pack on all three backends in one closeout pass
• add environment-to-environment reruns before turning local Docker numbers into sizing guidance

Short Conclusion

The engine is now backend-comparable on normalized performance across Oracle, PostgreSQL, and MongoDB.

The current picture is:

• Oracle is the most validated backend
• PostgreSQL is the best performance-to-operability compromise
• MongoDB is the fastest measured backend but not yet the safest backend recommendation