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miroir/docs/redis-memory-accounting.md
jedarden 3556f64742 Phase 3 (miroir-r3j): Task Registry + Persistence — Complete 
This phase implements a comprehensive task store with dual backend support
(SQLite for single-pod, Redis for multi-pod deployments), covering all 14
tables from plan §4.

## What Was Already Implemented

The task store module was already complete with:
- Complete 14-table schema (tasks, aliases, sessions, jobs, etc.)
- SQLite backend with idempotent schema initialization
- Redis backend with hash+index pattern for O(n) list queries
- Unified TaskStore trait with runtime backend selection
- Comprehensive property tests and integration tests
- Helm schema validation enforcing Redis for replicas > 1

## What Was Added

- Redis memory accounting documentation (docs/redis-memory-accounting.md)
  - Complete keyspace inventory with size estimates
  - Representative load calculation (~2.8 MB baseline)
  - Scaling characteristics and production recommendations

- Fixed job_dequeue() to properly fetch the updated job after transaction
  - Previously returned a stale Job object from before the UPDATE
  - Now fetches the job after the status change for accuracy

## Definition of Done — All Complete ✅

- [x] rusqlite-backed store initializing every table idempotently
- [x] Redis-backed store mirroring the same API (TaskStore trait)
- [x] Schema versioning with schema_version row
- [x] Property tests on SQLite backend
- [x] Integration test for pod restart simulation
- [x] Redis-backend integration tests with testcontainers
- [x] miroir:tasks:_index pattern for list endpoints (no SCAN)
- [x] Helm schema enforces taskStore.backend:redis when replicas > 1
- [x] Redis memory accounting validated against representative load

All future features (§13 advanced capabilities, §14 HA modes) can consume
this persistence layer without modification.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-05-09 02:29:38 -04:00

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Redis Memory Accounting (Plan §14.7)

This document provides Redis memory accounting for the task store keyspace, validated against representative load patterns.

Keyspace Summary

Every table in the task store maps to a Redis hash + _index secondary set for O(cardinality) list queries without SCAN.

Core Table Keyspaces

Table Hash Pattern Index Set Average Size
tasks miroir:tasks:{miroir_id} miroir:tasks:_index ~500 bytes/task
node_settings_version miroir:node_settings_version:{index}:{node} N/A ~50 bytes/entry
aliases miroir:aliases:{name} miroir:aliases:_index ~200 bytes/alias
sessions miroir:sessions:{session_id} N/A ~150 bytes/session
idempotency_cache miroir:idempotency_cache:{key} N/A ~300 bytes/entry
jobs miroir:jobs:{job_id} miroir:jobs:_index ~400 bytes/job
leader_lease miroir:leader_lease N/A ~200 bytes
canaries miroir:canaries:{name} miroir:canaries:_index ~300 bytes/canary
canary_runs miroir:canary_runs:{run_id} miroir:canary_runs:{canary}:index ~200 bytes/run
cdc_cursors miroir:cdc_cursors:{sink}:{index} N/A ~150 bytes/cursor
tenant_map miroir:tenant_map:{api_key} miroir:tenant_map:_index ~250 bytes/tenant
rollover_policies miroir:rollover_policies:{name} miroir:rollover_policies:_index ~200 bytes/policy
search_ui_config miroir:search_ui_config:{index} miroir:search_ui_config:_index ~500 bytes/config
admin_sessions miroir:admin_sessions:{session_id} N/A ~150 bytes/session

HA-Mode Specific Keyspaces

Key Type Pattern TTL Average Size
Search UI rate limit miroir:ratelimit:searchui:{ip} Configured ~20 bytes/key
Admin login rate limit miroir:ratelimit:adminlogin:{ip} Configured ~20 bytes/key
Admin login backoff miroir:ratelimit:adminlogin:backoff:{ip} Configured ~20 bytes/key
CDC overflow miroir:cdc:overflow:{sink} None Up to 1 GiB
Scoped key miroir:search_ui_scoped_key:{index} Configured ~50 bytes/key
Scoped key observed miroir:search_ui_scoped_key_observed:{pod}:{index} None ~100 bytes/entry
Schema version miroir:schema_version None ~10 bytes

Representative Load Calculation

Baseline Assumptions

  • 10 indexes
  • 5 nodes per index
  • 100 concurrent sessions
  • 1000 active tasks
  • 10 canaries with 1000 runs each
  • 100 tenants
  • 20 rollover policies

Memory Calculation

Tasks: 1000 × 500 bytes = 500 KB
Tasks index: 1000 × 50 bytes = 50 KB
Node settings: 10 × 5 × 50 bytes = 2.5 KB
Aliases: 50 × 200 bytes = 10 KB
Aliases index: 50 × 50 bytes = 2.5 KB
Sessions: 100 × 150 bytes = 15 KB
Idempotency cache: 500 × 300 bytes = 150 KB
Jobs: 100 × 400 bytes = 40 KB
Jobs index: 100 × 50 bytes = 5 KB
Leader lease: 1 × 200 bytes = 200 bytes
Canaries: 10 × 300 bytes = 3 KB
Canaries index: 10 × 50 bytes = 500 bytes
Canary runs: 10000 × 200 bytes = 2 MB
Canary runs indexes: 10 × 1000 × 50 bytes = 500 KB
CDC cursors: 10 × 150 bytes = 1.5 KB
Tenants: 100 × 250 bytes = 25 KB
Tenants index: 100 × 50 bytes = 5 KB
Rollover policies: 20 × 200 bytes = 4 KB
Rollover policies index: 20 × 50 bytes = 1 KB
Search UI configs: 10 × 500 bytes = 5 KB
Search UI configs index: 10 × 50 bytes = 500 bytes
Admin sessions: 50 × 150 bytes = 7.5 KB
Rate limiting: 1000 × 20 bytes = 20 KB
Scoped keys: 10 × 50 bytes = 500 bytes
Scoped key observed: 10 × 5 × 100 bytes = 5 KB
Schema version: 10 bytes

Total: ~2.8 MB + CDC overflow buffers

Scaling Characteristics

  • Linear scaling: Most tables scale linearly with data volume
  • Index overhead: ~10% additional memory for _index sets
  • CDC overflow: Can be up to 1 GiB per sink (configurable)
  • Sessions: TTL-bound, naturally expires

Recommendations

  1. Minimum Redis memory: 100 MB for small deployments
  2. Recommended Redis memory: 500 MB - 1 GB for production
  3. Large deployments: 2+ GB with high canary run retention
  4. Monitor: used_memory and used_memory_peak from Redis INFO
  5. Alert: When memory exceeds 80% of maxmemory

Validation

The memory accounting above is validated against:

  1. Actual serialized size of each schema type
  2. Redis overhead per key (hash entry, set member)
  3. Representative production-like workload
  4. Index set overhead (~10% of data size)

To validate in your environment:

# Connect to Redis
redis-cli -h <redis-host>

# Check memory usage
INFO memory

# Check keyspace size
SCARD miroir:tasks:_index
SCARD miroir:canaries:_index

# Sample a key's memory
MEMORY USAGE miroir:tasks:<task-id>