我一直听说 PHP 有开销.例如,C++ int 在 32 位系统上使用 4 个字节,但 PHP int 使用更多.这个值是多少?
I keep hearing that PHP has overhead. For example a C++ int uses 4 Bytes on a 32 bit system but a PHP int uses more. What is this value?
我需要比评论更多的空间来扩展 mario 的发现,所以我将添加一个答案.
I need more space than a comment to expand on mario's findings so I'll add an answer instead.
C union
的大小将是其最大成员的大小(可能带有额外的字节以满足对齐约束).对于 zvalue_value
,这将是具有三个指针大小的 obj
(不包括这些指针指向的内存所需的内存):
The size of a C union
will be the size of its largest member (possibly with extra bytes to satisfy alignment constraints). For zvalue_value
, that would be the obj
which has the size of three pointers (not including the memory required for what those pointers point to):
typedef struct _zend_object {
zend_class_entry *ce;
HashTable *properties;
HashTable *guards; /* protects from __get/__set ... recursion */
} zend_object;
在 32 位系统上,zend_object
将占用 24 个字节,而在 64 位系统上将占用 48 个字节.因此,每个 zvalue_value
将至少占用 24 或 48 个字节,无论您在其中存储什么数据.还有消耗更多内存的变量的名称;一旦编译器完成,编译语言通常会丢弃名称并将值视为简单的字节序列(因此 double
占用八个字节, char
占用一个字节,等等..).
On a 32bit system, a zend_object
will take 24 bytes while on a 64bit system it will take 48 bytes. So, every zvalue_value
will take at least 24 or 48 bytes regardless of what data you store in it. There's also the name of the variable which consumes more memory; compiled languages generally discard the names once the compiler is done and treat values as simple sequences of bytes (so a double
takes eight bytes, a char
takes one byte, etc...).
关于您最近关于 PHP 布尔值的问题,一个简单的布尔值将消耗 24 或 48 个字节作为值,再加上几个字节作为名称,再加上 4 或 8 个字节作为 zend_unit
, 加上四个(或八个)来表示这两个 zend_uchar
:
With regards to your recent questions about PHP booleans, a simple boolean value will consume 24 or 48 bytes for the value, plus a few more bytes for the name, plus four or eight for the zend_unit
, plus four (or eight) for the two zend_uchar
s in this:
struct _zval_struct {
/* Variable information */
zvalue_value value; /* value */
zend_uint refcount__gc;
zend_uchar type; /* active type */
zend_uchar is_ref__gc;
};
由于对齐限制,zend_uchar
成员将占用四个(或八个)字节,几乎每个 CPU 都希望访问自然地址边界上的内存,这意味着 zend_uchar
成员将占用四个(或八个)字节code>struct 将占用 4 个字节或 8 个字节的内存(取决于 CPU 的自然字长和对齐约束).因此,布尔值将占用 36 到 72 字节的内存.
The zend_uchar
members will chew up four (or eight) bytes due to alignment constraints, almost every CPU wants to access memory on natural address boundaries and that means that a single byte sized member of a struct
will take up four bytes or eight bytes of memory (depending on the CPUs natural word size and alignment constraints). So, a boolean will take somewhere between 36 and 72 bytes of memory.
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