Power to the People: Redis Lua Scripts
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The document discusses Lua, a powerful scripting language used in Redis, detailing its features and advantages for server-side scripting. It emphasizes the atomicity and blocking nature of scripts, their utility in reducing bandwidth, and data processing capabilities. Additionally, it mentions various use cases and limitations of using Lua within Redis, including debugging and replication concerns.
![Lua Redis language, primer (1/2)
--[[
this is a multi-line comment
]]
local t = { 1, 2, foo = "bar", nil, false }
for i, v in ipairs(KEYS)
if i % 2 ~= 0 then
redis.call('SET', ARGV[1],)
end
end](https://image.slidesharecdn.com/07-redis-lua-scripts-itamar-haber-redis-labs-160310182207/85/Power-to-the-People-Redis-Lua-Scripts-6-320.jpg)
![Lua Redis libraries, primer (2/2)
Core Lua: base, table, string, math & debug
Also included: bitop, struct, cmsgpack & cjson
redis library: call, pcall, log, status_reply,
Error_reply & sha1hex
[v3.2 spoiler]: debug, breakpoint, set_repl &
replicate_commands](https://image.slidesharecdn.com/07-redis-lua-scripts-itamar-haber-redis-labs-160310182207/85/Power-to-the-People-Redis-Lua-Scripts-7-320.jpg)
![Script source is sent to slaves, reduces wire traffic:
for i = 1, 100 do
redis.call('INCR', KEYS[1])
end
Disadvantages: wasteful (1 + n slaves), long recovery
from AOF, no non-determinism, no "transient" keys
Lua replication < v3.2](https://image.slidesharecdn.com/07-redis-lua-scripts-itamar-haber-redis-labs-160310182207/85/Power-to-the-People-Redis-Lua-Scripts-18-320.jpg)
Power to the People: Redis Lua Scripts
- 2. @itamarhaber A Redis Geek, Disque Freak... and Lunatic! Chief Developer Advocatique at Have you signed for newsletter? http://bit.ly/RedisWatch
- 3. ...is a powerful, fast, lightweight, embeddable scripting language. ...(pronounced LOO-ah) means "Moon" in Portuguese. Please do not write it as "LUA", which is both ugly and confusing... http://www.lua.org
- 4. Lunatic Noun: a mentally ill person (not in technical use), extremely foolish, eccentric, or absurd. Origin: Middle English, from Old French lunatique, from late Latin lunaticus, from Latin luna ‘moon’ (from the belief that change of the moon caused intermittent insanity).
- 5. Luaphobia is pure lunacy Redis does Lua since v2.6 (Oct 23, 2012) Scripts are atomic, have (practically) local data access Lua is pretty and/or ugly isn't perfect, but … … having the option to use it beats not. (mea culpa: when all you have is a hammer)
- 6. Lua Redis language, primer (1/2) --[[ this is a multi-line comment ]] local t = { 1, 2, foo = "bar", nil, false } for i, v in ipairs(KEYS) if i % 2 ~= 0 then redis.call('SET', ARGV[1],) end end
- 7. Lua Redis libraries, primer (2/2) Core Lua: base, table, string, math & debug Also included: bitop, struct, cmsgpack & cjson redis library: call, pcall, log, status_reply, Error_reply & sha1hex [v3.2 spoiler]: debug, breakpoint, set_repl & replicate_commands
- 8. Lua crash course... ceci n'est pas Le Voyage Dans Le Lune For your future reference: RTFM - http://www.lua.org/pil Redis - http://redis.io/commands/eval 15min - https://gist.github.com/tylerneylon/5853042
- 9. A poor & not to scale analogy Redis is the Sun. Earth is your application. Imagine that the Moon is stuck in the middle of the Sun. You send non-melting rockets (scripts) with robots (commands) and cargo (data) back and forth…
- 10. A helluava use case #1 Save the bandwidth, save the LATENCY ● Cached compiled multi-operations scripts ● Variadic keys & variable arity arguments (i.e. lots) ● Server-side processing for: exploding input, data transformation & manipulation, JSON/MessagePack (de)serialization, imploding (aggregating) output...
- 11. UC#1 example: GEOPATHLEN Meet https://github.com/RedisLabs/geo.lua (WIP) A (metric only) helper library for Redis geospatial indices Redis API: GEODIST key elem1 elem2 + GEODIST key elem2 elem3 + ... Lua library: GEOPATHLEN key elem1 elem2 elem3...
- 12. Winning use case #2 Transact with intelligence ● Scripts are atomic & blocking ● Comments, variables, data types, operators, control structures & (some) libraries ● Do you really want to WATCH/MULTI/DISCARD/EXEC? Lua.tx "recipe": 1) assert 2) process 3) check 4) commit
- 13. Liberating use case #3 Patent APIs & data structures Remember geo.lua? ● GEODEL ● xyzsets (geosets w/ attitude) ● GeoJSON - encode/decode ● ...and ME TRY FILTER!
- 14. GEORADIUS -> GEOMETRYFILTER 3. Radius search from pbb's center 2. Compute p's bounding box 4. Filter anything out of pbb 5. Use a semi-infinite ray (PNPOLY) Find the geoset members in polygon p 1. Read p's definition from geomash
- 15. Lua ain't only green cheese ● Massive number crunching? Nah: redimension's benchmark ● Lua's operators (no ternary?), strings (no split?), patterns (no regex?), tables (no zip?)... ● Only 32-bit bit operations ● Redis' sandboxing means no external packages ● Access to data not totally inexpensive ● Beware of returning doubles, associative arrays, …
- 17. SCRIPT DEBUG, YES PLEASE! Integral Redis Lua scripts debugger ZeroBrane Studio Plugin for Redis
- 18. Script source is sent to slaves, reduces wire traffic: for i = 1, 100 do redis.call('INCR', KEYS[1]) end Disadvantages: wasteful (1 + n slaves), long recovery from AOF, no non-determinism, no "transient" keys Lua replication < v3.2
- 19. Effects & target replication 3.2 -- succeeds if called before any write redis.replicate_commands() -- optionally, change replication target redis.set_repl(redis.REPL_NONE) -- or redis.REPL_AOF, redis.REPL_SLAVE -- or redis.REPL_ALL (the default) redis.call('TIME') -- random prize!
- 20. Lua versions ● Redis: 5.1.5 2012-02-17 ● Current: 5.3.2 2015-11-30 ● No major changes to language, upgrade TBD soon™ Scripts graveyard: infospect.lua, hitman.lua and redis- lua-debugger… but I can still add port 6379 to /etc/services with Lua though ;)