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Version 30 (modified by moo, 2 years ago) (diff)


Frequently Asked Questions

Where to get help?

freenode, channel #lighttpd
XCache @ googlegroups.

See GetSupport

Why XCache?

See Introduction

Where Is ./configure?

Well... you have to install php first, which gives you "phpize" executable(script), and do

~/src/xcache $ phpize
(generating configure)
~/src/xcache $ ./configure --help
~/src/xcache $ ./configure --enable-...

How to install from source?

follow the instructions in GettingSource, BuildingFromSource, InstallingAsPhpExtension

What if i'm getting "undefined symbol"

If your php is configured --enable-versioning, disable it. It's broken. If you insist on versioning, build XCache as a static module of php.

Apache2 keeps getting segmentation faults with cache larger than 4M

Set "xcache.readonly_protection = On" in php.ini

I get "Cannot dynamically load"

When u get PHP Warning: Unknown(): Cannot dynamically load - dynamic modules are not supported in Unknown on line 0, it's because your php is running on a arch/os that don't support dynamic load library(aka modules), to solve it:

build as static module
~ $ mv xcache php-src/ext/
~ $ cd php-src/
~/php-src $ ./buildconf --force
~/php-src $ ./config.nice --enable-xcache --enable-xcache-coverager
(or if you havn't run configure yet, use:)
~/php-src $ ./configure --enable-xcache --enable-xcache-coverager --your-options
~/php-src $ make all
~/php-src $ make install

Why is misses > 0 no matter how I increase the shm size?

"Misses" a opp to "hits". You get cache misses when there's nothing in the cache in the first time, after when it is cached and you starts getting cache hits. So there shall be at least misses=count(cached-php).

Why is my cache being cleared?

Set PHP_FCGI_CHILDREN to 1 or greater if you're using php FastCGI.

And see the following.

I see random "hits" in admin page

It is possible that "hits" count looks like random number in admin page. i.e.: you see hits=300,000 on first load of admin page, but dropped to hits=1 in 2nd reload and back to hits=312,456 on 3rd load.

This is because you have php started in different group which does not share shm with each other. But keep in mind that all childs in 1 group will share shm. So how to check and make it 1 group only?


Good Exmaple
$ pstree -p
        |              |-supervise(4913)---lighttpd(23975)-+-php-cgi(23979)-+-php-cgi(23981)
        |              |                                   |                |-php-cgi(23982)
        |              |                                   |                |-php-cgi(23983)
        |              |                                   |                `-php-cgi(23984)
Bad Exmaple
$ pstree -p
        |              |-supervise(4913)---lighttpd(23975)-+-php-cgi(23979)-+-php-cgi(23981)
        |              |                                   |                |-php-cgi(23982)
        |              |                                   |                |-php-cgi(23983)
        |              |                                   |                `-php-cgi(23984)
                       |                                   +-php-cgi(23980)-+-php-cgi(23985)
        |              |                                   |                |-php-cgi(23986)
        |              |                                   |                |-php-cgi(23987)
        |              |                                   |                `-php-cgi(23988)

See also:

Help! I get error about "XCache requires Zend Engine API version NNN"

XCache requires Zend Engine API version 220051025.
The Zend Engine API version 220060519 which is installed, is newer.
Contact mOo at for a later version of 

You get this error because you have an outdated build of XCache. i.e., you have upgraded php

Read next faq. undefined symbol: OnUpdateLong?

Read next faq. undefined symbol: core_globals_id

It can be *_globals_id or *_id. This error mean XCache was built with wrong PHP headers (the include/php/*.h files), either it was wrong version or wrong PHP built option, like 4.x vs 5.x or PHP zts built vs non-zts built. Apparently, it can be fixed easily by removing the wrong headers and rebuild XCache.

  1. Remove wrong PHP headers PHP headers can be php-devel package on some system, simply reinstall or upgrade it. But if your php is installed manually, try:
Remove PHP headers manually
(updatedb is optional if it's up to date already)
# updatedb
# locate include/php/main
(now, remove them)
# rm -rf /usr/lib64/php5/include/php/
# rm -rf /usr/local/include/php......
# cd php
(Reinstall the right php headers, using make)
php # make install
(or using apt-get install php5-dev, or however you install your php)
php # apt-get install php5-dev
  1. Rebuild XCache with the right php headers
Rebuild XCache
$ cd xcache
$ make distclean
$ phpize --clean
$ phpize
$ ./configure --enable-... && make
$ su
# make install

I got error: * is incompatible with XCache n Unknown on line 0

Use zend_extension=/path/to/ or zend_extension_ts=..., and make sure it's before any other zend_extension=...

I have read that xcache.optimizer setting gives an important performance gain. is that true ?

Currently only the "cacher" and "coverager" modules are implemented, tested and known to be working, the "optimizer" does nothing. it will be available only in XCache version 2, which is in an early development stage.