도움이 될지 모르겠지만 제 경우를 말씀드릴께요.. 일단 Xcache는 사용하지 않구요 eaccelerator 만 사용합니다.

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[root@localhost ~]# php -v
PHP 5.1.6 (cli) (built: Apr  7 2009 08:00:04)
Copyright (c) 1997-2006 The PHP Group
Zend Engine v2.1.0, Copyright (c) 1998-2006 Zend Technologies
    with eAccelerator v0.9.5.3, Copyright (c) 2004-2006 eAccelerator, by eAccelerator
[root@localhost ~]# locate eaccelerator.so
/usr/lib/php/modules/eaccelerator.so
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그리고 /etc/php.d/eaccelerator.ini 내용입니다

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[eaccelerator]

;;;;;;;;;;;;;;;;;;;
; About this file ;
;;;;;;;;;;;;;;;;;;;
;
; eAccelerator is compatible with Zend Optimizer's loader. Zend Optimizer
; must be installed after eAccelerator in php.ini. If you don't use scripts
; encoded with Zend Encoder then we do not recommend you install Zend Optimizer
; with eAccelerator.

; You must uncomment one (and only one) line from the following to load
; eAccelerator extension.
;extension="eaccelerator.so"
zend_extension="/usr/lib/php/modules/eaccelerator.so"
;zend_extension_ts="/usr/lib/php4/eaccelerator.so"
;extension="eaccelerator.dll"
;zend_extension_ts="c:\php4\eaccelerator.dll"
;zend_extension="c:\php4\eaccelerator.dll"

; The amount of shared memory (in megabytes) that eAccelerator will use.
; "0" means OS default. Default value is "0".
eaccelerator.shm_size = "0"

; The directory that is used for disk cache. eAccelerator stores precompiled
; code, session data, content and user entries  here. The same data can be
; stored in shared memory also (for more quick access). Default value is
; "/tmp/eaccelerator".
eaccelerator.cache_dir = "/tmp/eaccelerator"

; Enables or disables eAccelerator. Should be "1" for enabling or
; "0" for disabling. Default value is "1".
eaccelerator.enable = "1"

; Enables or disables internal peephole optimizer which may speed up code
; execution. Should be "1" for enabling or "0" for disabling.
; Default value is "1".
eaccelerator.optimizer = "1"

; Enables or disables debug logging. Setting this to 1 will print information
; to the log file about the cach hits of a file.
eaccelerator.debug = 0

; Set the log file for eaccelerator. When this option isn't set then the data
; will be logged to stderr
eaccelerator.log_file = "/var/log/httpd/eaccelerator_log"

; A string that's prepended to all keys. This allows two applications that use the
; same key names to run on the same host by setting this in .htaccess or in the main
; configuration file for the whole webserver.
eaccelerator.name_space = ""

; Enables or disables PHP file modification checking. Should be "1"
; for enabling or "0" for disabling. You should set it to "1" if you want
; to recompile PHP files after modification. Default value is "1".
eaccelerator.check_mtime = "1"

; Determine which PHP files must be cached. You may specify the number of
; patterns (for example "*.php *.phtml") which specifies to cache or
; not to cache. If pattern starts with the character "!", it means to ignore
; files which are matched by the following pattern. Default value is "" that
; means - all PHP scripts will be cached.
eaccelerator.filter = ""
; Disables putting large values into shared memory by "eaccelerator_put()"
; function.
; It indicates the largest allowed size in bytes (10240, 10K, 1M). The "0"
; disables the limit. Default value is "0".
eaccelerator.shm_max = "0"

; When eAccelerator fails to get shared memory for new script it removes
; all scripts which were not accessed at last "shm_ttl" seconds from shared
; memory. Default value is "0" that means - don't remove any files from
; shared memory.
eaccelerator.shm_ttl = "0"

; When eAccelerator fails to get shared memory for new script it tryes to
; remove old script if the previous try was made more then "shm_prune_period"
; seconds ago. Default value is "0" that means - don't try to remove any
; files from shared memory.
eaccelerator.shm_prune_period = "0"

; Enables or disables caching of compiled scripts on disk. It has no effect
; on session data and content caching.
; Default value is "0" that means - use disk and shared memory for caching.
eaccelerator.shm_only = "0"

; Enables or disables cached content compression. Default value is "1" that
; means enable compression.
eaccelerator.compress = "1"

; Compression level used for content caching.  Default value is "9" which i
; is the maximum compression level
eaccelerator.compress_level = "9"

; Determine where keys, session data and content will be cached. The possible
; values are:
; "shm_and_disk" - cache data in shared memory and on disk (default value)
; "shm"          - cache data in shared memory or on disk if shared memory
;                  is full or data size greater then "eaccelerator.shm_max"
; "shm_only"     - cache data in shared memory
; "disk_only"    - cache data on disk
; "none"         - don't cache data
eaccelerator.keys     = "shm_and_disk"
eaccelerator.sessions = "shm_and_disk"
eaccelerator.content  = "shm_and_disk"

; The script paths that are allowed to get admin information and do admin
; controls
eaccelerator.allowed_admin_path = ""
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이상입니다 도움이 되었으면 좋겠네요..

 

두가지 이상의 opcode cacher는 공존 할 수 없으니 eaccelerator, xcache 중 하나를 택일 하시고요. opcode cacher가 로딩 된 후 zend optimizer를 로딩하게 하면 됩니다. xcache의 coverager, optmizer 다 끄시고요. xcache 포럼을 안 살펴보신거 같네요. 거기에 정보 무지하게 많습니다.