MEMCACHED_REPLACE(3)

💖 MEMCACHED_REPLACE 💖 (3)

libmemcached-awesome girlies rise up ✨ today we're learning how to put stuff on the server and how to swap it out, and honestly? it's giving "closet restock but make it network calls" 🎀

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🌸 NAME 🌸

memcached_replace — Storing and Replacing Data 💾💅

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✨ SYNOPSIS ✨

#include <libmemcached/memcached.h>

Compile and link with -lmemcached

memcached_return_t memcached_set(memcached_st *ptr, const char *key,
size_t key_length, const char *value, size_t value_length, time_t
expiration, uint32_t flags)

memcached_return_t memcached_add(memcached_st *ptr, const char *key,
size_t key_length, const char *value, size_t value_length, time_t
expiration, uint32_t flags)

memcached_return_t memcached_replace(memcached_st *ptr, const char *key,
size_t key_length, const char *value, size_t value_length, time_t
expiration, uint32_t flags)

memcached_return_t memcached_set_by_key(memcached_st *ptr, const char
*group_key, size_t group_key_length, const char *key, size_t key_length,
const char *value, size_t value_length, time_t expiration, uint32_t
flags)

memcached_return_t memcached_add_by_key(memcached_st *ptr, const char
*group_key, size_t group_key_length, const char *key, size_t key_length,
const char *value, size_t value_length, time_t expiration, uint32_t
flags)

memcached_return_t memcached_replace_by_key(memcached_st *ptr, const
char *group_key, size_t group_key_length, const char *key, size_t
key_length, const char *value, size_t value_length, time_t expiration,
uint32_t flags)

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🦋 DESCRIPTION 🦋

okay so. memcached_set(), memcached_add(), and memcached_replace() are all about storing info on the server. Every single one of them takes a key, plus its length, so the object can be stored. Heads up bestie: keys are currently capped at 250 characters when you're using a version of memcached(1) that's 1.4 or below, or when you're using the text protocol. You must hand over both a value and a length. Optionally you can store the object. And also — keys are currently limited to 250 characters by the memcached(1) server. (Yeah, it's said twice. We move. 😌) You must supply both a value and a length. Optionally you may set an expiration time for the object, plus a 16 byte value (it's meant to be used as a bitmap 👀). And "flags"? That's a 4byte space stored right alongside the main value. Many sub libraries make use of this field, so in most cases users should avoid making use of it. like, don't touch it unless you know what you're doing, fr fr.

memcached_set() will write an object to the server. If an object already exists it will overwrite what's in the server. If the object does not exist it will be written. And if you're using the non-blocking mode, this function will always return true unless a network error occurs. slay, no blocking, no waiting 🫶

memcached_replace() replaces an object on the server. If the object is not found on the server, an error occurs. it's giving "you can't replace what was never there" 💀

memcached_add() adds an object to the server. If the object is found on the server, an error occurs — otherwise the value is stored. iconically picky 💅

memcached_set_by_key(), memcached_add_by_key(), and memcached_replace_by_key() all behave in a similar method as the non key methods. The difference? They use their group_key parameter to map objects to particular servers. so basically they know where to send your lil data 🎀

If you are looking for performance, memcached_set() with non-blocking IO is the fastest way to store data on the server. fastest. periodt. ⭐

All of the above functions are tested with the MEMCACHED_BEHAVIOR_USE_UDP behavior enabled. However — when using these operations with this behavior on, there are limits to the size of the payload being sent to the server. The reason for these limits is that the Memcached Server does not allow multi-datagram requests and the current server implementation sets a datagram size to 1400 bytes. Due to protocol overhead, the actual limit of the user supplied data is less than 1400 bytes and depends on the protocol in use, as well as the operation being executed. When running with the binary protocol, MEMCACHED_BEHAVIOR_BINARY_PROTOCOL, the size of the key, value, flags and expiry combined may not exceed 1368 bytes. When running with the ASCII protocol, the exact limit fluctuates depending on which function is being executed and whether the function is a cas operation or not. For non-cas ASCII set operations, there are at least 1335 bytes available to split among the key, key_prefix, and value; for cas ASCII operations there are at least 1318 bytes available to split among the key, key_prefix and value. If the total size of the command, including overhead, exceeds 1400 bytes, a MEMCACHED_WRITE_FAILURE will be returned. 😭

🚨 bestie listen. UDP mode has real ceilings. do the math on your key + key_prefix + value BEFORE you send, or you're getting a MEMCACHED_WRITE_FAILURE and a bad vibe check.

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💜 RETURN VALUE 💜

All methods return a value of type memcached_return_t.

On success the value will be MEMCACHED_SUCCESS. Use memcached_strerror() to translate this value to a printable string. 🎀

For memcached_replace() and memcached_add(), MEMCACHED_NOTSTORED is a legitimate error in the case of a collision. not a bug, not a crash, just the universe saying "that key was taken" 🙈

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🌈 SEE ALSO 🌈

• memcached(1)
• libmemcached(3)
• memcached_strerror(3)
• memcached_prepend(3)
• memcached_append(3)
• memcached_cas(3)

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and that's the whole page, bestie 🫶 this one is from libmemcached-awesome, version 1.1, dated Jul 24, 2025 — and yes, she's an icon, she's a legend, and she is the moment 👑✨ bye ily, go store something 💖