XCache

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Overview

XCache is a PHP opcode cacher. It improves performance for PHP applications by caching compiled PHP code in memory for later requests.

More information can be found on the XCache website:

How to make XCache available

XCache is an on-demand available option to DreamHost VPS users, on a per-domain basis, or can be set up for all domains to use.

Enabling XCache in the panel

  1. Navigate to the (Panel > ‘Domains’ > ‘Manage Domains’) page.
  2. Click the Edit button to the right of your domain under the ‘Web Hosting’ column.
    01 xcache panel.fw.png
  3. Under the ‘Web Options’ section, enable the checkbox titled ‘PHP XCache Support’.

Configuring XCache

If you can view XCache through a phpinfo() file, then you can configure it through a custom PHP.ini file by using the following settings:

Note2 icon.png Note: The file can be added after the Zend Optimizer settings.


[xcache]
; ini only settings, all the values here is default unless explained

; select low level shm/allocator scheme implementation
xcache.shm_scheme =        "mmap"
; to disable: xcache.size=0
; to enable : xcache.size=64M etc (any size > 0) and your system mmap allows
xcache.size  =                64M
; set to cpu count (cat /proc/cpuinfo |grep -c processor)
xcache.count =                 2
; just a hash hints, you can always store count(items) > slots
xcache.slots =                8k
; ttl of the cache item, 0=forever
xcache.ttl   =                 0
; interval of gc scanning expired items, 0=no scan, other values is in seconds
xcache.gc_interval =           0

; same as above but for variable cache
xcache.var_size  =            0M
xcache.var_count =             1
xcache.var_slots =            8K
; default ttl
xcache.var_ttl   =             0
xcache.var_maxttl   =          0
xcache.var_gc_interval =     300

xcache.test =                Off
; N/A for /dev/zero
xcache.readonly_protection = Off
; for *nix, xcache.mmap_path is a file path, not directory.
; Use something like "/tmp/xcache" if you want to turn on ReadonlyProtection
; 2 group of php won't share the same /tmp/xcache

; leave it blank(disabled) or "/tmp/phpcore/"
; make sure it's writable by php (without checking open_basedir)
xcache.coredump_directory =   ""

; per request settings
xcache.cacher =               On
xcache.stat   =               On
xcache.optimizer =           On

[xcache.coverager]
; per request settings
; enable coverage data collecting for xcache.coveragedump_directory and xcache_$
xcache.coverager =          Off

; ini only settings
; make sure it's readable (care open_basedir) by coverage viewer script
; requires xcache.coverager=On
xcache.coveragedump_directory = ""

XCache best practices

Be sure to adhere to the following best practices when using XCache:

  • For WordPress sites, the W3TC WordPress cache plugin and the DreamHost version of XCache may conflict. For maximum compatibility, be sure that the W3TC plugin setting ‘Enhanced Disk Caching’ is enabled as this will enable the static file caching.
  • For DreamPress sites, DreamHost recommends that you do not combine the use of XCache and the W3TC cache plugin. Instead, only choose one for your site.
  • Enabling XCache will increase overall memory usage, however it will also speed up page loading time. It is designed to use memory and it increases memory usage because each site needs to spawn its own PHP processes with a custom config. If your site is experiencing memory limit issues, you may want to disable XCache during any debugging process. Other caching options can be found on the Caching your Site wiki.

See also