WordPress站点上的APC缓存碎片

Question

我最近在网站服务器（Centos 5.7，PHP 5.3,1.5GB内存）上安装并激活了APC缓存，主要用于中等流量（30k独立访客/月）WordPress网站的运行设置为使用APC进行数据库和对象缓存的W3Total缓存（页面，缩小使用磁盘）。

服务器的APC信息页面显示存在始终严重的碎片。例如，在重新启动httpd后，11小时后碎片率高达75％，几天后我已经看到它为100％。在任何时候，我都没有看到使用超过40％的高速缓存，服务器一直运行在大约400Mb的内存，1100Mb空闲（ -/+缓冲区/缓存，由free -m报告）。所以它似乎没有导致碎片的内存不足。

我开始使用默认的APC和W3TC配置，并且已经尝试的以下变化的各种组合： -

• apc.ttl减少到1800（从7200）
• apc.user_ttl设置为0 （使用用户的高速缓存的唯一事情是W3TC并设置其自己的TTL）
• W3TC超时从180到7200秒增加
• apc.filters到方框timthumb

尽管到目前为止，Google网站管理员工具所测量的主观性能和页面加载时间似乎没有受到任何影响，但这些更改似乎没有太大差别。

我应该为此担心吗？虽然目前的表现不是，但我宁愿在服务器负载/站点流量上升之前进行排序。如果担心，我可以采取哪些措施来解决？

编辑： - 下面是完整的apc.ini配置文件： -

; Enable apc extension module 
extension = apc.so 

; Options for the APC module version >= 3.1.3 
; See http://www.php.net/manual/en/apc.configuration.php 

; This can be set to 0 to disable APC. 
apc.enabled=1 
; The number of shared memory segments to allocate for the compiler cache. 
apc.shm_segments=1 
; The size of each shared memory segment, with M/G suffixe 
apc.shm_size=256M 
; A "hint" about the number of distinct source files that will be included or 
; requested on your web server. Set to zero or omit if you're not sure; 
apc.num_files_hint=1024 
; Just like num_files_hint, a "hint" about the number of distinct user cache 
; variables to store. Set to zero or omit if you're not sure; 
apc.user_entries_hint=4096 
; The number of seconds a cache entry is allowed to idle in a slot in case this 
; cache entry slot is needed by another entry. 
apc.ttl=7200 
; use the SAPI request start time for TTL 
apc.use_request_time=1 
; The number of seconds a user cache entry is allowed to idle in a slot in case 
; this cache entry slot is needed by another entry. 
apc.user_ttl=0 
; The number of seconds that a cache entry may remain on the garbage-collection list. 
apc.gc_ttl=3600 
; On by default, but can be set to off and used in conjunction with positive 
; apc.filters so that files are only cached if matched by a positive filter. 
apc.cache_by_default=1 
; A comma-separated list of POSIX extended regular expressions. 
apc.filters="-.[omitted]/timthumb.php$" 
; The mktemp-style file_mask to pass to the mmap module 
apc.mmap_file_mask=/tmp/apc.XXXXXX 
; This file_update_protection setting puts a delay on caching brand new files. 
apc.file_update_protection=2 
; Setting this enables APC for the CLI version of PHP (Mostly for testing and debugging). 
apc.enable_cli=0 
; Prevents large files from being cached 
apc.max_file_size=1M 
; Whether to stat the main script file and the fullpath includes. 
apc.stat=1 
; Vertification with ctime will avoid problems caused by programs such as svn or rsync by making 
; sure inodes havn't changed since the last stat. APC will normally only check mtime. 
apc.stat_ctime=0 
; Whether to canonicalize paths in stat=0 mode or fall back to stat behaviour 
apc.canonicalize=0 
; With write_lock enabled, only one process at a time will try to compile an 
; uncached script while the other processes will run uncached 
apc.write_lock=1 
; Logs any scripts that were automatically excluded from being cached due to early/late binding issues. 
apc.report_autofilter=0 
; RFC1867 File Upload Progress hook handler 
apc.rfc1867=0 
apc.rfc1867_prefix =upload_ 
apc.rfc1867_name=APC_UPLOAD_PROGRESS 
apc.rfc1867_freq=0 
apc.rfc1867_ttl=3600 
; Optimize include_once and require_once calls and avoid the expensive system calls used. 
apc.include_once_override=0 
apc.lazy_classes=0 
apc.lazy_functions=0 
; Enables APC handling of signals, such as SIGSEGV, that write core files when signaled. 
; APC will attempt to unmap the shared memory segment in order to exclude it from the core file 
apc.coredump_unmap=0 
; Records a md5 hash of files. 
apc.file_md5=0 
; not documented 
apc.preload_path 

UPDATE我也posted on WP forums并得到了W3TotalCache笔者这样的响应： -

那次经历在某些网站上并不出乎意料。我将在下一个版本中研究 缓存逻辑以提高APC性能。

所以好像W3TotalCache是​​碎片的根本原因。

Answer 1

尝试增加APC使用的段大小的大小。只使用一个分段。还可以从您创建的子域访问wp管理界面。

Optimize APC Caching

如果您的服务器上的其他虚拟主机，并不需要指令缓存，可以为这些网站禁用APC。您可以通过在apc.ini文件中设置apc.cache_by_default=0并将php_flag apc.cache_by_default On置于wp根目录中的.htaccess文件中来在vhost级别上执行此操作。这应该是碎片化的原因。

文件中的更改也会导致分段。编辑后的文件将被删除，新文件将被添加到缓存中。如果你还没有做，你也应该设置apc.stat=0。这将通过不检查每次文件是否更改来提高整体性能。

如果你不希望WP Admin被缓存，你可以创建一个像admin.example.com这样的子域，你可以访问管理面板。通过这样做，您将能够禁用操作码缓存。这也将减少碎片。

更新： 禁用对象缓存和数据库缓存有助于减少碎片。用于对象缓存的Us'ng redis或memcached以及仅用于操作码缓存的APC可解决此问题。