本文目录一览：
- 1、PHP.ini 中每一句前面的分号代表什么意思
- 2、php安装的问题，无法载入 mysql 扩展，请检查 PHP 配置
- 3、想做个 网站 ，求一段PHP编程代码,PHP的MYSQL缓存怎么实现？ 最好举个例子。
- 4、如何修改MySQL导入数据库文件最大限制2048KB的方法
- 5、PHP如何取得mysql字段值并记算时间？
PHP.ini 中每一句前面的分号代表什么意思
1、php.ini文件是扩展文件。
2、每一行前面的分号代表禁用该扩展。
3、只需删除该分号，就能打开相应扩展。
4、修改php.ini后一定要保存文件并且重启php运行环境才能见效。
php安装的问题，无法载入 mysql 扩展，请检查 PHP 配置
首先你需要将PHP安装目录下的php_mysql.dll和php_mysqli.dll（我的在D:\apptools\php5\ext目录下）复制到c:\windows\system32目录下，然后修改php.ini文件（需要放到c:\windows目录下），关键是extension=php_mysql.dll 和extension_dir = "D:/apptools/php5/ext"。 -phpmysql.cachesize
我的配置是这样的：
[PHP]
;;;;;;;;;;;
; WARNING ;
;;;;;;;;;;;
; This is the default settings file for new PHP installations.
; By default, PHP installs itself with a configuration suitable for
; development purposes, and *NOT* for production purposes.
; For several security-oriented considerations that should be taken
; before going online with your site, please consult php.ini-recommended
; and .
;;;;;;;;;;;;;;;;;;;
; About php.ini ;
;;;;;;;;;;;;;;;;;;;
; This file controls many aspects of PHP's behavior. In order for PHP to
; read it, it must be named 'php.ini'. PHP looks for it in the current
; working directory, in the path designated by the environment variable
; PHPRC, and in the path that was defined in compile time (in that order).
; Under Windows, the compile-time path is the Windows directory. The
; path in which the php.ini file is looked for can be overridden using
; the -c argument in command line mode.
;
; The syntax of the file is extremely simple. Whitespace and Lines
; beginning with a semicolon are silently ignored (as you probably guessed).
; Section headers (e.g. [Foo]) are also silently ignored, even though
; they might mean something in the future.
;
; Directives are specified using the following syntax:
; directive = value
; Directive names are *case sensitive* - foo=bar is different from FOO=bar.
;
; The value can be a string, a number, a PHP constant (e.g. E_ALL or M_PI), one
; of the INI constants (On, Off, True, False, Yes, No and None) or an expression
; (e.g. E_ALL ~E_NOTICE), or a quoted string ("foo").
;
; Expressions in the INI file are limited to bitwise operators and parentheses:
; | bitwise OR
; bitwise AND
; ~ bitwise NOT
; ! boolean NOT
;
; Boolean flags can be turned on using the values 1, On, True or Yes.
; They can be turned off using the values 0, Off, False or No.
;
; An empty string can be denoted by simply not writing anything after the equal
; sign, or by using the None keyword:
;
; foo = ; sets foo to an empty string
; foo = none ; sets foo to an empty string
; foo = "none" ; sets foo to the string 'none'
;
; If you use constants in your value, and these constants belong to a
; dynamically loaded extension (either a PHP extension or a Zend extension),
; you may only use these constants *after* the line that loads the extension.
;
;
;;;;;;;;;;;;;;;;;;;
; About this file ;
;;;;;;;;;;;;;;;;;;;
; All the values in the php.ini-dist file correspond to the builtin
; defaults (that is, if no php.ini is used, or if you delete these lines,
; the builtin defaults will be identical).
;;;;;;;;;;;;;;;;;;;;
; Language Options ;
;;;;;;;;;;;;;;;;;;;;
; Enable the PHP scripting language engine under Apache.
engine = On
; Enable compatibility mode with Zend Engine 1 (PHP 4.x)
zend.ze1_compatibility_mode = Off
; Allow the ? tag. Otherwise, only ?php and script tags are recognized.
; NOTE: Using short tags should be avoided when developing applications or
; libraries that are meant for redistribution, or deployment on PHP
; servers which are not under your control, because short tags may not
; be supported on the target server. For portable, redistributable code,
; be sure not to use short tags.
short_open_tag = On
; Allow ASP-style % % tags.
asp_tags = Off
; The number of significant digits displayed in floating point numbers.
precision = 12
; Enforce year 2000 compliance (will cause problems with non-compliant browsers)
y2k_compliance = On
; Output buffering allows you to send header lines (including cookies) even
; after you send body content, at the price of slowing PHP's output layer a
; bit. You can enable output buffering during runtime by calling the output
; buffering functions. You can also enable output buffering for all files by
; setting this directive to On. If you wish to limit the size of the buffer
; to a certain size - you can use a maximum number of bytes instead of 'On', as
; a value for this directive (e.g., output_buffering=4096).
output_buffering = On
; You can redirect all of the output of your scripts to a function. For
; example, if you set output_handler to "mb_output_handler", character
; encoding will be transparently converted to the specified encoding.
; Setting any output handler automatically turns on output buffering.
; Note: People who wrote portable scripts should not depend on this ini
; directive. Instead, explicitly set the output handler using ob_start().
; Using this ini directive may cause problems unless you know what script
; is doing.
; Note: You cannot use both "mb_output_handler" with "ob_iconv_handler"
; and you cannot use both "ob_gzhandler" and "zlib.output_compression".
; Note: output_handler must be empty if this is set 'On' !!!!
; Instead you must use zlib.output_handler.
;output_handler =
; Transparent output compression using the zlib library
; Valid values for this option are 'off', 'on', or a specific buffer size
; to be used for compression (default is 4KB)
; Note: Resulting chunk size may vary due to nature of compression. PHP
; outputs chunks that are few hundreds bytes each as a result of
; compression. If you prefer a larger chunk size for better
; performance, enable output_buffering in addition.
; Note: You need to use zlib.output_handler instead of the standard
; output_handler, or otherwise the output will be corrupted.
zlib.output_compression = Off
; You cannot specify additional output handlers if zlib.output_compression
; is activated here. This setting does the same as output_handler but in
; a different order.
;zlib.output_handler =
; Implicit flush tells PHP to tell the output layer to flush itself
; automatically after every output block. This is equivalent to calling the
; PHP function flush() after each and every call to print() or echo() and each
; and every HTML block. Turning this option on has serious performance
; implications and is generally recommended for debugging purposes only.
implicit_flush = Off
; The unserialize callback function will be called (with the undefined class'
; name as parameter), if the unserializer finds an undefined class
; which should be instantiated.
; A warning appears if the specified function is not defined, or if the
; function doesn't include/implement the missing class.
; So only set this entry, if you really want to implement such a
; callback-function.
unserialize_callback_func=
; When floats doubles are serialized store serialize_precision significant
; digits after the floating point. The default value ensures that when floats
; are decoded with unserialize, the data will remain the same.
serialize_precision = 100
; Whether to enable the ability to force arguments to be passed by reference
; at function call time. This method is deprecated and is likely to be
; unsupported in future versions of PHP/Zend. The encouraged method of
; specifying which arguments should be passed by reference is in the function
; declaration. You're encouraged to try and turn this option Off and make
; sure your scripts work properly with it in order to ensure they will work
; with future versions of the language (you will receive a warning each time
; you use this feature, and the argument will be passed by value instead of by
; reference).
allow_call_time_pass_reference = On
;
; Safe Mode
;
safe_mode = Off
; By default, Safe Mode does a UID compare check when
; opening files. If you want to relax this to a GID compare,
; then turn on safe_mode_gid.
safe_mode_gid = Off
; When safe_mode is on, UID/GID checks are bypassed when
; including files from this directory and its subdirectories.
; (directory must also be in include_path or full path must
; be used when including)
safe_mode_include_dir =
; When safe_mode is on, only executables located in the safe_mode_exec_dir
; will be allowed to be executed via the exec family of functions.
safe_mode_exec_dir =
; Setting certain environment variables may be a potential security breach.
; This directive contains a comma-delimited list of prefixes. In Safe Mode,
; the user may only alter environment variables whose names begin with the
; prefixes supplied here. By default, users will only be able to set
; environment variables that begin with PHP_ (e.g. PHP_FOO=BAR).
;
; Note: If this directive is empty, PHP will let the user modify ANY
; environment variable!
safe_mode_allowed_env_vars = PHP_
; This directive contains a comma-delimited list of environment variables that
; the end user won't be able to change using putenv(). These variables will be
; protected even if safe_mode_allowed_env_vars is set to allow to change them.
safe_mode_protected_env_vars = LD_LIBRARY_PATH
; open_basedir, if set, limits all file operations to the defined directory
; and below. This directive makes most sense if used in a per-directory
; or per-virtualhost web server configuration file. This directive is
; *NOT* affected by whether Safe Mode is turned On or Off.
;open_basedir =
; This directive allows you to disable certain functions for security reasons.
; It receives a comma-delimited list of function names. This directive is
; *NOT* affected by whether Safe Mode is turned On or Off.
disable_functions =
; This directive allows you to disable certain classes for security reasons.
; It receives a comma-delimited list of class names. This directive is
; *NOT* affected by whether Safe Mode is turned On or Off.
disable_classes =
; Colors for Syntax Highlighting mode. Anything that's acceptable in
; span style="color: ???????" would work.
;highlight.string = #DD0000
;highlight.comment = #FF9900
;highlight.keyword = #007700
;highlight.bg = #FFFFFF
;highlight.default = #0000BB
;highlight.html = #000000
; If enabled, the request will be allowed to complete even if the user aborts
; the request. Consider enabling it if executing long request, which may end up
; being interrupted by the user or a browser timing out.
; ignore_user_abort = On
;
; Misc
;
; Decides whether PHP may expose the fact that it is installed on the server
; (e.g. by adding its signature to the Web server header). It is no security
; threat in any way, but it makes it possible to determine whether you use PHP
; on your server or not.
expose_php = On
;;;;;;;;;;;;;;;;;;;
; Resource Limits ;
;;;;;;;;;;;;;;;;;;;
max_execution_time = 3000 ; Maximum execution time of each script, in seconds
max_input_time = 60 ; Maximum amount of time each script may spend parsing request data
memory_limit = 8M ; Maximum amount of memory a script may consume (8MB)
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Error handling and logging ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; error_reporting is a bit-field. Or each number up to get desired error
; reporting level
; E_ALL - All errors and warnings (doesn't include E_STRICT)
; E_ERROR - fatal run-time errors
; E_WARNING - run-time warnings (non-fatal errors)
; E_PARSE - compile-time parse errors
; E_NOTICE - run-time notices (these are warnings which often result
; from a bug in your code, but it's possible that it was
; intentional (e.g., using an uninitialized variable and
; relying on the fact it's automatically initialized to an
; empty string)
; E_STRICT - run-time notices, enable to have PHP suggest changes
; to your code which will ensure the best interoperability
; and forward compatibility of your code
; E_CORE_ERROR - fatal errors that occur during PHP's initial startup
; E_CORE_WARNING - warnings (non-fatal errors) that occur during PHP's
; initial startup
; E_COMPILE_ERROR - fatal compile-time errors
; E_COMPILE_WARNING - compile-time warnings (non-fatal errors)
; E_USER_ERROR - user-generated error message
; E_USER_WARNING - user-generated warning message
; E_USER_NOTICE - user-generated notice message
;
; Examples:
;
; - Show all errors, except for notices and coding standards warnings
;
;error_reporting = E_ALL ~E_NOTICE
;
; - Show all errors, except for notices
;
;error_reporting = E_ALL ~E_NOTICE | E_STRICT
;
; - Show only errors
;
;error_reporting = E_COMPILE_ERROR|E_ERROR|E_CORE_ERROR
;
; - Show all errors except for notices and coding standards warnings
;
error_reporting = E_ALL ~E_NOTICE
; Print out errors (as a part of the output). For production web sites,
; you're strongly encouraged to turn this feature off, and use error logging
; instead (see below). Keeping display_errors enabled on a production web site
; may reveal security information to end users, such as file paths on your Web
; server, your database schema or other information.
display_errors = On
; Even when display_errors is on, errors that occur during PHP's startup
; sequence are not displayed. It's strongly recommended to keep
; display_startup_errors off, except for when debugging.
display_startup_errors = Off
; Log errors into a log file (server-specific log, stderr, or error_log (below))
; As stated above, you're strongly advised to use error logging in place of
; error displaying on production web sites.
log_errors = Off
; Set maximum length of log_errors. In error_log information about the source is
; added. The default is 1024 and 0 allows to not apply any maximum length at all.
log_errors_max_len = 1024
; Do not log repeated messages. Repeated errors must occur in same file on same
; line until ignore_repeated_source is set true.
ignore_repeated_errors = Off
; Ignore source of message when ignoring repeated messages. When this setting
; is On you will not log errors with repeated messages from different files or
; sourcelines.
ignore_repeated_source = Off
; If this parameter is set to Off, then memory leaks will not be shown (on
; stdout or in the log). This has only effect in a debug compile, and if
; error reporting includes E_WARNING in the allowed list
report_memleaks = On
; Store the last error/warning message in $php_errormsg (boolean).
track_errors = Off
; Disable the inclusion of HTML tags in error messages.
; Note: Never use this feature for production boxes.
;html_errors = Off
; If html_errors is set On PHP produces clickable error messages that direct
; to a page describing the error or function causing the error in detail.
; You can download a copy of the PHP manual from
; and change docref_root to the base URL of your local copy including the
; leading '/'. You must also specify the file extension being used including
; the dot.
; Note: Never use this feature for production boxes.
;docref_root = "/phpmanual/"
;docref_ext = .html
; String to output before an error message.
;error_prepend_string = "font color=ff0000"
; String to output after an error message.
;error_append_string = "/font"
; Log errors to specified file.
;error_log = filename
; Log errors to syslog (Event Log on NT, not valid in Windows 95).
;error_log = syslog
;;;;;;;;;;;;;;;;;
; Data Handling ;
;;;;;;;;;;;;;;;;;
;
; Note - track_vars is ALWAYS enabled as of PHP 4.0.3
; The separator used in PHP generated URLs to separate arguments.
; Default is "".
;arg_separator.output = ""
; List of separator(s) used by PHP to parse input URLs into variables.
; Default is "".
; NOTE: Every character in this directive is considered as separator!
;arg_separator.input = ";"
; This directive describes the order in which PHP registers GET, POST, Cookie,
; Environment and Built-in variables (G, P, C, E S respectively, often
; referred to as EGPCS or GPC). Registration is done from left to right, newer
; values override older values.
variables_order = "EGPCS"
; Whether or not to register the EGPCS variables as global variables. You may
; want to turn this off if you don't want to clutter your scripts' global scope
; with user data. This makes most sense when coupled with track_vars - in which
; case you can access all of the GPC variables through the $HTTP_*_VARS[],
; variables.
;
; You should do your best to write your scripts so that they do not require
; register_globals to be on; Using form variables as globals can easily lead
; to possible security problems, if the code is not very well thought of.
register_globals = On
; Whether or not to register the old-style input arrays, HTTP_GET_VARS
; and friends. If you're not using them, it's recommended to turn them off,
; for performance reasons.
register_long_arrays = On
; This directive tells PHP whether to declare the argvargc variables (that
; would contain the GET information). If you don't use these variables, you
; should turn it off for increased performance.
register_argc_argv = On
; When enabled, the SERVER and ENV variables are created when they're first
; used (Just In Time) instead of when the script starts. If these variables
; are not used within a script, having this directive on will result in a
; performance gain. The PHP directives register_globals, register_long_arrays,
; and register_argc_argv must be disabled for this directive to have any affect.
auto_globals_jit = On
; Maximum size of POST data that PHP will accept.
post_max_size = 8M
; Magic quotes
;
; Magic quotes for incoming GET/POST/Cookie data.
magic_quotes_gpc = On
; Magic quotes for runtime-generated data, e.g. data from SQL, from exec(), etc.
magic_quotes_runtime = Off
; Use Sybase-style magic quotes (escape ' with '' instead of \').
magic_quotes_sybase = Off
; Automatically add files before or after any PHP document.
auto_prepend_file =
auto_append_file =
; As of 4.0b4, PHP always outputs a character encoding by default in
; the Content-type: header. To disable sending of the charset, simply
; set it to be empty.
;
; PHP's built-in default is text/html
default_mimetype = "text/html"
;default_charset = "iso-8859-1"
; Always populate the $HTTP_RAW_POST_DATA variable.
;always_populate_raw_post_data = On
;;;;;;;;;;;;;;;;;;;;;;;;;
; Paths and Directories ;
;;;;;;;;;;;;;;;;;;;;;;;;;
; UNIX: "/path1:/path2"
;include_path = ".:/php/includes"
;
; Windows: "\path1;\path2"
include_path = ".;D:\apptools\php5\PEAR"
; The root of the PHP pages, used only if nonempty.
; if PHP was not compiled with FORCE_REDIRECT, you SHOULD set doc_root
; if you are running php as a CGI under any web server (other than IIS)
; see documentation for security issues. The alternate is to use the
; cgi.force_redirect configuration below
doc_root =
; The directory under which PHP opens the script using /~username used only
; if nonempty.
user_dir =
; Directory in which the loadable extensions (modules) reside.
extension_dir = "D:/apptools/php5/ext"
; Whether or not to enable the dl() function. The dl() function does NOT work
; properly in multithreaded servers, such as IIS or Zeus, and is automatically
; disabled on them.
enable_dl = On
想做个 网站 ，求一段PHP编程代码,PHP的MYSQL缓存怎么实现？ 最好举个例子。
数据库属于 IO 密集型的应用程序，其主要职责就是数据的管理及存储工作。而我们知道，从内存中读取一个数据库的时间是微秒级别，而从一块普通硬盘上读取一个IO是在毫秒级别，二者相差3个数量级。所以，要优化数据库，首先第一步需要优化的就是 IO，尽可能将磁盘IO转化为内存IO。本文先从 MySQL 数据库IO相关参数(缓存参数)的角度来看看可以通过哪些参数进行IO优化：-phpmysql.cachesize
•query_cache_size/query_cache_type (global)
Query cache 作用于整个 MySQL Instance，主要用来缓存 MySQL 中的 ResultSet，也就是一条SQL语句执行的结果集，所以仅仅只能针对select语句。当我们打开了 Query Cache 功能，MySQL在接受到一条select语句的请求后，如果该语句满足Query Cache的要求(未显式说明不允许使用Query Cache，或者已经显式申明需要使用Query Cache)，MySQL 会直接根据预先设定好的HASH算法将接受到的select语句以字符串方式进行hash，然后到Query Cache 中直接查找是否已经缓存。也就是说，如果已经在缓存中，该select请求就会直接将数据返回，从而省略了后面所有的步骤(如 SQL语句的解析，优化器优化以及向存储引擎请求数据等)，极大的提高性能。-phpmysql.cachesize
当然，Query Cache 也有一个致命的缺陷，那就是当某个表的数据有任何任何变化，都会导致所有引用了该表的select语句在Query Cache 中的缓存数据失效。所以，当我们的数据变化非常频繁的情况下，使用Query Cache 可能会得不偿失。-phpmysql.cachesize
Query Cache的使用需要多个参数配合，其中最为关键的是 query_cache_size 和 query_cache_type ，前者设置用于缓存 ResultSet 的内存大小，后者设置在何场景下使用 Query Cache。在以往的经验来看，如果不是用来缓存基本不变的数据的MySQL数据库，query_cache_size 一般 256MB 是一个比较合适的大小。当然，这可以通过计算Query Cache的命中率(Qcache_hits/(Qcache_hits+Qcache_inserts)*100))来进行调整。query_cache_type可以设置为0(OFF)，1(ON)或者2(DEMOND)，分别表示完全不使用query cache，除显式要求不使用query cache(使用sql_no_cache)之外的所有的select都使用query cache，只有显示要求才使用query cache(使用sql_cache)。-phpmysql.cachesize
•binlog_cache_size (global)
Binlog Cache 用于在打开了二进制日志(binlog)记录功能的环境，是 MySQL 用来提高binlog的记录效率而设计的一个用于短时间内临时缓存binlog数据的内存区域。
一般来说，如果我们的数据库中没有什么大事务，写入也不是特别频繁，2MB～4MB是一个合适的选择。但是如果我们的数据库大事务较多，写入量比较大，可与适当调高binlog_cache_size。同时，我们可以通过binlog_cache_use 以及 binlog_cache_disk_use来分析设置的binlog_cache_size是否足够，是否有大量的binlog_cache由于内存大小不够而使用临时文件(binlog_cache_disk_use)来缓存了。-phpmysql.cachesize
•key_buffer_size (global)
Key Buffer 可能是大家最为熟悉的一个 MySQL 缓存参数了，尤其是在 MySQL 没有更换默认存储引擎的时候，很多朋友可能会发现，默认的 MySQL 配置文件中设置最大的一个内存参数就是这个参数了。key_buffer_size 参数用来设置用于缓存 MyISAM存储引擎中索引文件的内存区域大小。如果我们有足够的内存，这个缓存区域最好是能够存放下我们所有的 MyISAM 引擎表的所有索引，以尽可能提高性能。-phpmysql.cachesize
此外，当我们在使用MyISAM 存储的时候有一个及其重要的点需要注意，由于 MyISAM 引擎的特性限制了他仅仅只会缓存索引块到内存中，而不会缓存表数据库块。所以，我们的 SQL 一定要尽可能让过滤条件都在索引中，以便让缓存帮助我们提高查询效率。-phpmysql.cachesize
•bulk_insert_buffer_size (thread)
和key_buffer_size一样，这个参数同样也仅作用于使用 MyISAM存储引擎，用来缓存批量插入数据的时候临时缓存写入数据。当我们使用如下几种数据写入语句的时候，会使用这个内存区域来缓存批量结构的数据以帮助批量写入数据文件：-phpmysql.cachesize
insert … select …
insert … values (…) ,(…),(…)…
load data infile… into… (非空表)
•innodb_buffer_pool_size(global)
当我们使用InnoDB存储引擎的时候，innodb_buffer_pool_size 参数可能是影响我们性能的最为关键的一个参数了，他用来设置用于缓存 InnoDB 索引及数据块的内存区域大小，类似于 MyISAM 存储引擎的 key_buffer_size 参数，当然，可能更像是 Oracle 的 db_cache_size。简单来说，当我们操作一个 InnoDB 表的时候，返回的所有数据或者去数据过程中用到的任何一个索引块，都会在这个内存区域中走一遭。-phpmysql.cachesize
和key_buffer_size 对于 MyISAM 引擎一样，innodb_buffer_pool_size 设置了 InnoDB 存储引擎需求最大的一块内存区域的大小，直接关系到 InnoDB存储引擎的性能，所以如果我们有足够的内存，尽可将该参数设置到足够打，将尽可能多的 InnoDB 的索引及数据都放入到该缓存区域中，直至全部。-phpmysql.cachesize
我们可以通过 (Innodb_buffer_pool_read_requests – Innodb_buffer_pool_reads) / Innodb_buffer_pool_read_requests * 100% 计算缓存命中率，并根据命中率来调整 innodb_buffer_pool_size 参数大小进行优化。-phpmysql.cachesize
•innodb_additional_mem_pool_size(global)
这个参数我们平时调整的可能不是太多，很多人都使用了默认值，可能很多人都不是太熟悉这个参数的作用。innodb_additional_mem_pool_size 设置了InnoDB存储引擎用来存放数据字典信息以及一些内部数据结构的内存空间大小，所以当我们一个MySQL Instance中的数据库对象非常多的时候，是需要适当调整该参数的大小以确保所有数据都能存放在内存中提高访问效率的。-phpmysql.cachesize
这个参数大小是否足够还是比较容易知道的，因为当过小的时候，MySQL 会记录 Warning 信息到数据库的 error log 中，这时候你就知道该调整这个参数大小了。
•innodb_log_buffer_size (global)
这是 InnoDB 存储引擎的事务日志所使用的缓冲区。类似于 Binlog Buffer，InnoDB 在写事务日志的时候，为了提高性能，也是先将信息写入 Innofb Log Buffer 中，当满足 innodb_flush_log_trx_commit 参数所设置的相应条件(或者日志缓冲区写满)之后，才会将日志写到文件(或者同步到磁盘)中。可以通过 innodb_log_buffer_size 参数设置其可以使用的最大内存空间。-phpmysql.cachesize
注：innodb_flush_log_trx_commit 参数对 InnoDB Log 的写入性能有非常关键的影响。该参数可以设置为0，1，2，解释如下：
0：log buffer中的数据将以每秒一次的频率写入到log file中，且同时会进行文件系统到磁盘的同步操作，但是每个事务的commit并不会触发任何log buffer 到log file的刷新或者文件系统到磁盘的刷新操作;-phpmysql.cachesize
1：在每次事务提交的时候将log buffer 中的数据都会写入到log file，同时也会触发文件系统到磁盘的同步;
2：事务提交会触发log buffer 到log file的刷新，但并不会触发磁盘文件系统到磁盘的同步。此外，每秒会有一次文件系统到磁盘同步操作。
此外，MySQL文档中还提到，这几种设置中的每秒同步一次的机制，可能并不会完全确保非常准确的每秒就一定会发生同步，还取决于进程调度的问题。实际上，InnoDB 能否真正满足此参数所设置值代表的意义正常 Recovery 还是受到了不同 OS 下文件系统以及磁盘本身的限制，可能有些时候在并没有真正完成磁盘同步的情况下也会告诉 mysqld 已经完成了磁盘同步。-phpmysql.cachesize
•innodb_max_dirty_pages_pct (global)
这个参数和上面的各个参数不同，他不是用来设置用于缓存某种数据的内存大小的一个参数，而是用来控制在 InnoDB Buffer Pool 中可以不用写入数据文件中的Dirty Page 的比例(已经被修但还没有从内存中写入到数据文件的脏数据)。这个比例值越大，从内存到磁盘的写入操作就会相对减少，所以能够一定程度下减少写入操作的磁盘IO。-phpmysql.cachesize
但是，如果这个比例值过大，当数据库 Crash 之后重启的时间可能就会很长，因为会有大量的事务数据需要从日志文件恢复出来写入数据文件中。同时，过大的比例值同时可能也会造成在达到比例设定上限后的 flush 操作“过猛”而导致性能波动很大。-phpmysql.cachesize
上面这几个参数是 MySQL 中为了减少磁盘物理IO而设计的主要参数，对 MySQL 的性能起到了至关重要的作用。
如何修改MySQL导入数据库文件最大限制2048KB的方法
非root用户运行MySQL，当MySQL配置比较高时，MySQL运行中生效的参数值与配置的值不一样,所以具体分析一下MySQL是怎么调整这些参数值的。
这篇文章的目的是为了说明在系统资源不够的情况下，MySQL 是怎么调整者三个参数的。说明此文涉及到三个参数open_files_limit、 max_connections、 table_open_cache。与这三个参数相关的系统资源是打开文件数限制，即文件描述符（fd）限制。系统参数与文件描述符的关系 - max_connection fd : 每一个MySQL connection 都需要一个文件描述符；-phpmysql.cachesize
- table_open_cache fd 打开一张表至少需要一个 文件描述符，如打开MyISAM需要两个fd ；
- 系统最大打开文件数可以通过 ulimit -n查看。MySQL调整参数的方式
根据配置（三个参数的配置值或默认值）计算 request_open_files（需要的文件描述符）；
2.获取有效的系统的限制值effective_open_files； 3.根据effective_open_files调整request_open_files； 4.根据调整后的request_open_files,计算实际生效的参数值（show variables 可查看参数值）。计算request_open_filesrequest_open_files有三个计算公式：1. // 最大连接数+同时打开的表的最大数量+其他（各种日志等等）2. limit_1= max_connections+table_cache_size * 2 + 10;3. 4. //假设平均每个连接打开的表的数量（2-4）5. //源码中是这么写的：6. //We are trying to allocate no less than 7. // max_connections*5 file handles8. limit_2= max_connections * 5;9. 10. //mysql 默认的默认是500011. limit_3= open_files_limit ? open_files_limit : 5000;12. 13. 所以open_files_limit期待的最低14. request_open_files= max(limit_1,limit_2,limit_3);计算effective_open_files:MySQL 的思路： -phpmysql.cachesize
在有限值的的范围内MySQL 尽量将effective_open_files的值设大。
修正request_open_files
requested_open_files= min(effective_open_files, request_open_files)
重新计算参数值
修正open_files_limit
open_files_limit = effective_open_files
修正max_connections
max_connections 根据 request_open_files 来做修正。1. limit = requested_open_files - 10 - TABLE_OPEN_CACHE_MIN * 2;-phpmysql.cachesize
如果配置的max_connections值大于limit，则将max_connections 的值修正为limit
其他情况下 max_connections 保留配置值
修正table_cache_size
table_cache_size 会根据 request_open_files 来做修正1. // mysql table_cache_size 最小值，4002. limit1 = TABLE_OPEN_CACHE_MIN3. // 根据 requested_open_files 计算4. limit2 = (requested_open_files - 10 - max_connections) / 25. limit = max(limit1,limt2);-phpmysql.cachesize
如果配置的table_cache_size 值大于limit，则将 table_cache_size 的值修正为limit
其他情况下table_cache_size 保留配置值
举例
以下用例在非 root 用户下运行
参数设置：
//mysql
max_connections = 500
table_open_cache = 999
//ulimit -n
1500
生效的值：
open_files_limit = 1500 max_connections = min[(1500 - 10 - 800),500] = 500
table_open_cache = ( 1500 - 10 - 500) / 2 =495
PHP如何取得mysql字段值并记算时间？
两种方式 ：
1、可以直接用SQL 里的函数 sum() ;
如："select sum(字段) as num from tab "; //sum 取该字段所有列的总和
2、用PHP函数 sum($array) ； //取数组中值的总和
当然 字段必须是int型的
