Re: How deep is copy on write?

On Wednesday, January 19, 2011 4:45:14 pm Ben Schmidt wrote: > > Related: What is the overhead of a ZVal? I'm assuming it's a fixed > > number of bytes. > > It seems not, though a zval has a fixed size. What that size is will > depend on the compiler and architecture of the system being used, or at > least on the ABI. Ah, yes, of course. Oh C... *snip* > The zvalue_value union will probably be 8 or 12 bytes, depending on the > architecture. The whole struct will then probably be between 14 and 24 > bytes, depending on the architecture and structure alignment and so on. *snip* > You can figure out what you think the overhead is from that. For a > string, arguably the whole structure is overhead, since the string is > stored elsewhere via pointer. Likewise for objects. For a double, the > payload is 8 bytes, and stored in the zval, so there's less overhead. An > integer, with a payload of 4 bytes, is somewhere in between. Hm. OK, so if I'm assuming a 64-bit architecture (most servers these days, I'd think) and just looking for a rough approximation, it sounds like 20 bytes per zval/variable is a not unreasonable estimation. At least close enough for determining the memory overhead of a general algorithm. Thanks again! --Larry Garfield