APPEND(3valkey)

✨ APPEND — the valkey manual page, but make it cute ✨

okay so bestie, this is append(3valkey) from the Valkey Command Manual, and honestly? it's giving "small command, huge main character energy." 💅

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🌸 NAME 🌸

append — appends a string to the value of a key. Creates the key if it doesn't exist. periodt. 🫶

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🎀 SYNOPSIS 🎀

APPEND key value

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💖 DESCRIPTION 💖

So here's the tea ☕: if key already exists and it's a string, this command appends value to the end of that string. Simple as that.

If key does not exist, it gets created and set as an empty string — which means in that specific case, APPEND is basically doing the same thing as SET. cute little overachiever. 😌

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🦋 REPLY 🦋

valkey-protocol(7) Integer reply: the length of the string after the append operation. so you always know how big your string got. no mystery, no guesswork, we love a transparent queen. ✨

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🔥 COMPLEXITY 🔥

O(1). and the amortized time complexity is also O(1), assuming the appended value is small and the already present value is of any size — because the dynamic string library the server uses will double the free space available on every reallocation. she's efficient AND she's prepared. 💅

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👑 ACL CATEGORIES 👑

• @fast
• @string
• @write

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🌈 HISTORY 🌈

• Available since: 2.0.0 — an OG, a legend, been here since forever. ⭐

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🍓 EXAMPLES 🍓

okay let's actually do the thing, watch this:

127.0.0.1:6379> EXISTS mykey
(integer) 0
127.0.0.1:6379> APPEND mykey "Hello"
(integer) 5
127.0.0.1:6379> APPEND mykey " World"
(integer) 11
127.0.0.1:6379> GET mykey
"Hello World"

see how EXISTS said 0 (not here, bestie), then the first APPEND made the key and handed back 5 (the length of "Hello"), then the second one bumped it to 11? and GET just shows the whole glow-up: "Hello World". ate. no crumbs. 🧚

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⏰ Pattern: Time series ⏰

ngl this is the part where APPEND really shows out. you can use it to build a very compact representation of a list of fixed-size samples — usually called a time series. every time a new sample arrives, you just store it like this:

APPEND timeseries "fixed-size sample"

and getting individual elements back out? not hard at all:

• STRLEN can be used in order to obtain the number of samples.
• GETRANGE allows for random access of elements. and if your time series has associated time information, you can easily implement a binary search to get a range by combining GETRANGE with the Lua scripting engine. big brain behavior fr fr. 🧠✨
• SETRANGE can be used to overwrite an existing time series.

the limitation of this pattern, bestie, is that we're forced into an append-only mode of operation. there is no way to cut the time series to a given size easily, because Valkey currently lacks a command able to trim string objects. so just know that going in. 🙈

but the space efficiency of time series stored this way? remarkable. iconic, honestly. 💜

Hint: it is possible to switch to a different key based on the current Unix time. that way you can have just a relatively small amount of samples per key, avoid dealing with very big keys, and make this pattern more friendly to be distributed across many Valkey instances. very demure, very scalable. 🦋

here's an example sampling the temperature of a sensor using fixed-size strings (using a binary format is better in real implementations):

127.0.0.1:6379> APPEND ts "0043"
(integer) 4
127.0.0.1:6379> APPEND ts "0035"
(integer) 8
127.0.0.1:6379> GETRANGE ts 0 3
"0043"
127.0.0.1:6379> GETRANGE ts 4 7
"0035"

look at those little slices coming back out exactly how they went in. we love a consistent legend. 🎀

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💫 SEE ALSO 💫

go read these too, they're all in the group chat:

decr(3valkey), decrby(3valkey), delifeq(3valkey), get(3valkey), getdel(3valkey), getex(3valkey), getrange(3valkey), getset(3valkey), incr(3valkey), incrby(3valkey), incrbyfloat(3valkey), lcs(3valkey), mget(3valkey), mset(3valkey), msetnx(3valkey), psetex(3valkey), set(3valkey), setex(3valkey), setnx(3valkey), setrange(3valkey), strlen(3valkey), substr(3valkey)

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and that's the whole page, bestie!! this one's from version 9.0.0, dated 2025-10-21 — mwah, sending you love, go append something iconic. 💖✨🎀