After event sourcing (25 Oct), this post covers pub/sub: topics, fanout topologies, delivery guarantees, slow-consumer isolation, DLQ, schemas, ACLs and metrics versus queues and outbox.

प्रकाशनसदस्यता: A Metrical Codification of Publish-Subscribe (with English glosses)

What this post is about

Publish-subscribe delivers each published message to many independent subscribers.

Topics covered

1. One-to-many delivery
2. Topic and routing contracts
3. Fanout vs routed topologies
4. At-least-once and idempotent handlers
5. Slow subscriber isolation
6. Per-subscription DLQ
7. Schema on payloads
8. Publish/subscribe ACLs
9. Lag and depth metrics
10. Queue vs pub/sub vs outbox

Sanskrit title

प्रकाशनसदस्यता = prakāśana-sadasyatā “publication-membership” (pub/sub).

English

Minimizable; Sanskrit-first.

ग्राह्यम् / Keep

१. named topics: documented routing
२. idempotent subscribers: duplicate safe
३. isolate slow subs: private buffers
४. DLQ per sub: with alerts
५. schema validate: on produce
६. ACL both ways: pub and sub
७. per-sub lag metrics: ops visibility

त्याज्यम् / Avoid

• one shared queue for all subscriber speeds
• open publish to any service account
• assume exactly-once without handler care

पदच्छेदः
एकः वदति बहवः शृण्वन्ति यदि पङ्क्तिः पृथक् । प्रकाशनसदस्यता तस्माद् बहुश्रुतिः ॥१॥

Word-for-word

Gloss table

English sense
Pub/sub fans one published message out to many independent subscribers without the publisher knowing each consumer.

Context / topic
Topic: why pub/sub. Distinct from point-to-point queues.

वृत्तमिति: ८-८-८-८।

पदच्छेदः
topic exchange subject स्पष्टम् । गूढrouting भ्रान्तिः ॥२॥

Word-for-word

Gloss table

English sense
Name topics and routing keys as a public contract. Undocumented wildcards become silent coupling.

Context / topic
Topic: topic design.

वृत्तमिति: ८-८-८-८।

पदच्छेदः
fanout vs routing vs topic modes । एकं न सर्वकर्म ॥३॥

Word-for-word

Gloss table

English sense
Choose broadcast, direct key, or pattern topic semantics on purpose. The wrong mode floods or starves consumers.

Context / topic
Topic: delivery topology.

वृत्तमिति: ८-८-८-८।

पदच्छेदः
at-least-once default; exactly-once दुःसाध्यम् । subscriber इदमर्थः ॥४॥

Word-for-word

Gloss table

English sense
Assume duplicates. Make handlers idempotent rather than promising perfect once-only bus magic.

Context / topic
Topic: delivery guarantees.

वृत्तमिति: ८-८-८-८।

पदच्छेदः
slow consumer isolation per-sub queue । एकमन्दः सर्वान् मा दहतु ॥५॥

Word-for-word

Gloss table

English sense
Isolate slow subscribers so they cannot back up the publisher or other listeners. Backpressure per subscription.

Context / topic
Topic: slow consumer isolation. Links to backpressure.

वृत्तमिति: एकादशाक्षराः पादाः।

पदच्छेदः
poison message DLQ per subscription । retry storm मा ॥६॥

Word-for-word

Gloss table

English sense
After N failures park the message on a DLQ with metrics and a human path.

Context / topic
Topic: poison handling. Links to queues.

वृत्तमिति: ८-८-८-८।

पदच्छेदः
schema on payload कोषेण । अरूपbytes युद्धाय ॥७॥

Word-for-word

Gloss table

English sense
Validate pub/sub payloads with the schema registry so subscribers do not break on silent field renames.

Context / topic
Topic: schemas on the bus.

वृत्तमिति: ८-८-८-८।

पदच्छेदः
authz who may publish/subscribe । open topic भये ॥८॥

Word-for-word

Gloss table

English sense
Lock publish and subscribe rights. An open topic is a cross-team foot-gun.

Context / topic
Topic: bus authz.

वृत्तमिति: ८-८-८-८।

पदच्छेदः
lag depth inflight metrics per sub । अदृश्यसदस्यः प्रेतः ॥९॥

Word-for-word

Gloss table

English sense
Operate each subscription like a queue: lag, age, error rate, DLQ depth.

Context / topic
Topic: ops metrics.

वृत्तमिति: ८-८-८-८।

पदच्छेदः
सन्देशपङ्क्तिः एकः एकम् प्रकाशनं एकः बहून् । आउटबॉक्स जन्म रक्षति ॥१०॥

Word-for-word

Gloss table

English sense
Queues are typically competing consumers; pub/sub is fan-out. Outbox still decides atomic birth with the DB transaction.

Context / topic
Topic: queue vs pub/sub vs outbox.

सन्धिः: पङ्क्तिः स्पर्धा; सदस्यता प्रसारः; पटलः जन्म।

वृत्तमिति: एकादशाक्षराः पादाः।

पदच्छेदः
topic topology idempotency isolation ACL metrics पञ्चकम् । एभिः प्रकाशनसदस्यता बहुश्रुतिसमन्विता ॥११॥

Word-for-word

Gloss table

English sense
Five limbs: clear topics, chosen topology, idempotent handlers, slow-consumer isolation with ACLs and per-sub metrics.

Context / topic
Topic: checklist.

वृत्तमिति: ८-८-८-८।

पदच्छेदः
इति प्रकाशनसदस्यतासारो बहुश्रुतिसमन्वितः । मितं प्रसारं क्रियायोग्यं तन्त्रधर्मः स उच्यते ॥१२॥

Word-for-word

Gloss table

English sense
Closing: speak once, let many hear, but isolate the slow and the poisoned.

Context / topic
Topic: close.

उपसंहारन्यायः: एकं वद; बहून् पृथक् श्रावय; मन्दं मा सर्वान् दह।

वृत्तमिति: ८-८-८-८।

१. Why pub/sub
२. Topics
३. Topologies
४. Guarantees
५. Slow isolation
६. DLQ
७. Schemas
८. ACL
९. Metrics
१०. Queue/outbox
११. Five limbs
१२. Close

1. Prior: queues 2026-07-29; outbox 2026-09-28; schema registry 2026-10-24; backpressure 2026-10-07.
2. Domain: publish-subscribe messaging.
3. English minimizable; Sanskrit-first.
4. Style: no em dash; no Oxford comma in English clauses.