Iterate Redis keys without blocking using SCAN with cursor, MATCH and COUNT
domain: redis.io · 7 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Start iteration with cursor 0: `SCAN 0` returns `[next-cursor, [keys...]]`.
Pass the returned cursor into the next call: `SCAN <cursor>`; the full iteration finishes when the server returns cursor "0" again - always loop until 0, don't stop based on an empty key list.
Filter with a glob pattern: `SCAN 0 MATCH user:*`.
Control work per call with COUNT (hint, default 10): `SCAN 0 MATCH user:* COUNT 1000` - raise COUNT when patterns are sparse so iterations return more matches.
Filter by type: `SCAN 0 TYPE string` (whole-db SCAN only).
For large/small collections inside a single key use the family: SSCAN (sets), HSCAN (hashes), ZSCAN (sorted sets) - for those the first arg is the key name.
Always treat returned keys as possibly duplicated - scan guarantees every element present for the whole iteration is eventually returned, but can return some elements multiple times.
Known gotchas
NEVER use KEYS in production - it blocks the server for seconds on large DBs; SCAN is the non-blocking cursor alternative.
MATCH filtering happens AFTER elements are retrieved server-side, so it doesn't reduce work - sparse patterns can return 0 keys on most iterations, which is normal until the cursor hits 0.
A full iteration is not a point-in-time snapshot - keys added/removed during iteration may or may not be returned; handle duplicates idempotently.
GeoHashes/HLLs/Bitfields are internally stored as strings/zsets, so SCAN TYPE can't reliably distinguish them.
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