More String Commands
The Wordcraft home screen shows the coin totals of four friends. Four GET commands mean four trips across the network, and each trip usually costs far more time than Redis spends answering. A handful of extra string commands save those trips and cover the cases SET, GET and INCR do not.
The rule
One command, many keys: batch the trips, not just the work.
MSET and MGET set or read several string keys in a single command.
127.0.0.1:6379> MSET coins:asha 120 coins:ravi 75 coins:tom 300
OK
127.0.0.1:6379> MGET coins:asha coins:ravi coins:meera coins:tom
1) "120"
2) "75"
3) (nil)
4) "300"The reply has one entry per key, in the order you asked. A key that is missing (or holds a non-string type) gives (nil) in its slot, so positions always line up. MSET replies OK and, like SET, replaces old values.
INCRBY and INCRBYFLOAT change a number by any amount. INCRBY takes whole numbers (negative ones too); INCRBYFLOAT handles decimals and replies with the result as a string:
127.0.0.1:6379> SET rating:asha 4.5
OK
127.0.0.1:6379> INCRBYFLOAT rating:asha 0.25
"4.75"GETRANGE key start end reads part of a string by byte positions, counting from 0, with both ends included. Negative positions count from the end, so -1 is the last byte.
127.0.0.1:6379> SET word:today planet
OK
127.0.0.1:6379> GETRANGE word:today 0 2
"pla"
127.0.0.1:6379> GETRANGE word:today -3 -1
"net"GETDEL key returns the value and deletes the key in one step, useful for one-time codes. SETRANGE overwrites bytes from a position, and MSETNX sets several keys only if none of them exist.
The shortcut
When your app is about to send the same command in a loop, ask: is there an M- version or a -BY version? Several GETs become one MGET; several INCRs become one INCRBY.
Spot the loop
The code calls
GETonce per friend: four round trips.
The trap with MSET is forgetting that it has no per-key options: it cannot set an expiry, and it replaces every key it names. When each key needs its own lifetime, send separate SET ... EX commands, ideally batched together by your client library.
Drills
Answer fast — trust the rule.
Only a and c exist, holding "1" and "3". What does MGET a b c return?
word:today holds "planet". What does GETRANGE word:today 2 4 return?
price holds "10". What does INCRBYFLOAT price 2.5 reply?
code:asha holds "7731". What does GET code:asha reply after GETDEL code:asha?
Remember
- One command, many keys: batch the trips, not just the work.
- Before looping a command, look for its M- or -BY version.
- MGET keeps positions: a missing key is a nil slot, not a shorter reply.