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Module 5 · APIs & Application LayerDay 04320 min

Pagination, Filtering, Sorting

Cursors beat offsets at scale.

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Day 043

Pagination, Filtering, Sorting

Client
client
API
service
DB index seek
datastore
Signal path
Cursor pagination flow
Client
client
cursor=…
API
service
API
service
flow
DB index seek
datastore
Memory hook

Pagination, Filtering, Sorting: cursors beat offsets at scale

Mental model

turn boundaries into contracts

Design lens

Cursor-only loses 'jump to page 10'.

Recall anchors
OffsetCursorFilters

Why it matters

Offset pagination is simple but slow at deep pages and unstable under writes. Cursor pagination uses a stable key and scales to billions of rows.

Deep dive

Offset: SELECT … OFFSET 10000 LIMIT 20 — DB must read 10020 rows.

Cursor: WHERE id > :last LIMIT 20 — index seek, fast.

Total counts are often expensive; consider 'has_more' instead.

Filters/sorts must match indexes or queries get slow at scale.

Demo / scenario

Browse latest posts; deep pagination is slow.

  1. Replace OFFSET with WHERE created_at < :cursor.
  2. Index (created_at, id) supports it.
  3. Drop totalCount endpoint; use 'next' cursor only.
  4. P99 drops from 1500ms to 50ms at deep pages.

Tradeoffs

  • Cursor-only loses 'jump to page 10'.
  • Mixed sort orders need composite cursors.
  • Total counts can be cached approximate.

Diagram

cursor=…
Client
API
DB index seek
Cursor pagination flow.

Mind map

Check yourself

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Sources & further reading

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