【揭秘Memcached内存管理】高效策略与实战技巧解析

引言

Memcached，作为一款高机能的分布式内存缓存体系，在减轻数据库负载、晋升Web效劳器机能方面发挥侧重要感化。其内存管理战略是Memcached高效运转的关键。本文将深刻剖析Memcached的内存管理机制，包含Slab Allocation、内存碎片处理、缓存优化战略等，并供给实战技能。

Memcached内存管理概述

Memcached的内存管理重要依附于Slab Allocation机制，该机制将内存分割成多个slab，每个slab包含多个牢固大小的chunk，以存储差别大小的数据项。这种计划旨在增加内存碎片，进步内存利用率。

Slab Allocation机制

Slab Class

Memcached将内存分别为多个slab class，每个class包含雷同大小的chunk。chunk的大小根据数据项的大小停止分别，以增加内存碎片。

#define SLABCLASS_SLABCLASSNAME(slabclass) (slabclass->name)
#define SLABCLASS_SIZE(slabclass) (slabclass->size)

Slab Class分配

Memcached根据数据项的大小抉择合适的slab class停止分配。假如数据项大小与某个slab class的chunk大小不婚配，则抉择最濒临的slab class。

slabclass_t *slabs_get(slabclass_t *s) {
    assert(s);
    assert(s->size > 0);
    assert(s->limit > 0);
    assert(s->num < s->limit);
    return s;
}

Slab Class开释

当数据项从缓存中删除时，Memcached会将其开释回对应的slab class。

”`c void item_return_to_slab(item *it) {

assert(it);
assert(it->slabslab);
assert(it->size <= it->slabslab->size);
assert(it->size > 0);
assert(it->slabslab->slabs);
assert(it->slabslab->slabs[it->slabslab->num]);
assert(it->slabslab->slabs[it->slabslab->num]->slabs);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num < it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->limit);
assert(it->slabslab->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->slabs[it->slabslab->num]->num