我最近在 Web 服务器(Centos 5.7、PHP 5.3、1.5Gb RAM)上安装并激活了 APC 缓存，该服务器主要专用于中等流量(每月 3 万独立访客)WordPress 站点，运行 W3Total Cache，设置为使用 APC 进行数据库和对象缓存(页面、缩小使用磁盘)。

服务器的 APC 信息页面显示一直存在大量碎片。例如，重启 httpd 后，碎片在 11 小时后达到 75%，几天后我看到它达到 100%。我从来没有见过超过 40% 的高速缓存内存被使用，并且服务器始终以大约 400Mb 内存使用，1100Mb 空闲(-/+ 缓冲区/缓存，由 free -m 报告)运行。所以它似乎不是导致碎片的内存不足。

我从默认的 APC 和 W3TC 配置开始，并尝试了以下更改的各种组合:-

• apc.ttl 减少到 1800(从 7200)
• apc.user_ttl 设置为 0(唯一使用用户缓存的是 W3TC，它设置自己的 TTL)
• W3TC 超时从 180 秒增加到 7200 秒
• apc.filters 来阻止 timthumb

这些更改似乎都没有产生太大影响，但到目前为止，由 Google 网站站长工具测量的主观性能和页面加载时间似乎并未受到任何影响。

我应该为此担心吗？虽然当前的性能表明没有，但我宁愿在服务器负载/站点流量增加之前对此进行排序。如果有问题，我可以采取哪些步骤来解决？

编辑:- 这是完整的 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

更新 我也是posted on WP forums并从 W3TotalCache 的作者那里得到了这个回复:-

That experience is not unexpected on some sites. I will be working on the caching logic in the next release to improve APC performance.

所以看起来 W3TotalCache 是碎片化的根本原因。

最佳答案

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

Optimize APC Caching

如果您的服务器上有其他不需要操作码缓存的虚拟主机，您可以为这些站点禁用 APC。您可以通过在 apc.ini 文件中设置 apc.cache_by_default=0 在 vhost 级别上执行此操作，并将 php_flag apc.cache_by_default On 放在 wp 上的 .htaccess 文件中根目录。这应该是碎片化的原因。

文件中的更改也可能导致碎片化。已编辑的文件将被删除，新文件将添加到缓存中。如果您还没有设置，您还应该设置 apc.stat=0。这将提高整体性能，因为不会每次都检查文件是否已更改。

如果您不希望 WP Admin 被缓存，您可以创建一个子域，例如 admin.example.com，然后您可以访问管理面板。通过这样做，您将能够禁用操作码缓存。这也将减少碎片化。

更新: 禁用对象缓存和数据库缓存有助于减少碎片。使用 ng redis 或 memcached 进行对象缓存，使用 APC 仅进行操作码缓存可以解决问题。

关于php - WordPress 网站上的 APC 缓存碎片，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/9292330/