<p>innodb_buffer_pool_size是整个MySQL服务器最重要的变量。</p><p>1. 为什么需要innodb buffer pool？</p><p>在MySQL5.5之前，广泛使用的和默认的存储引擎是MyISAM。MyISAM使用操作系统缓存来缓存数据。InnoDB需要innodb buffer pool中处理缓存。所以非常需要有足够的InnoDB buffer pool空间。</p><p>2. MySQL InnoDB buffer pool 里包含什么？</p><p>数据缓存</p><p>InnoDB数据页面</p><p>索引缓存</p><p>索引数据</p><p>缓冲数据</p><p>脏页（在内存中修改尚未刷新(写入)到磁盘的数据）</p><p>内部结构</p><p>如自适应哈希索引，行锁等。</p><p>3. 如何设置innodb_buffer_pool_size?</p><p>innodb_buffer_pool_size默认大小为128M。最大值取决于CPU的架构。在32-bit平台上，最大值为2**32 -1,在64-bit平台上最大值为2**64-1。当缓冲池大小大于1G时，将innodb_buffer_pool_instances设置大于1的值可以提高服务器的可扩展性。</p><p>大的缓冲池可以减小多次磁盘I/O访问相同的表数据。在专用数据库服务器上，可以将缓冲池大小设置为服务器物理内存的80%。</p><p>3.1 配置缓冲池大小时，请注意以下潜在问题</p><p>物理内存争用可能导致操作系统频繁的paging</p><p>InnoDB为缓冲区和control structures保留了额外的内存，因此总分配空间比指定的缓冲池大小大约大10％。</p><p>缓冲池的地址空间必须是连续的，这在带有在特定地址加载的DLL的Windows系统上可能是一个问题。</p><p>初始化缓冲池的时间大致与其大小成比例。在具有大缓冲池的实例上，初始化时间可能很长。要减少初始化时间，可以在服务器关闭时保存缓冲池状态，并在服务器启动时将其还原。</p><p>innodb_buffer_pool_dump_pct：指定每个缓冲池最近使用的页面读取和转储的百分比。 范围是1到100。默认值是25。例如，如果有4个缓冲池，每个缓冲池有100个page，并且innodb_buffer_pool_dump_pct设置为25，则dump每个缓冲池中最近使用的25个page。</p><p>innodb_buffer_pool_dump_at_shutdown：默认启用。指定在MySQL服务器关闭时是否记录在InnoDB缓冲池中缓存的页面，以便在下次重新启动时缩短预热过程。</p><p>innodb_buffer_pool_load_at_startup：默认启用。指定在MySQL服务器启动时，InnoDB缓冲池通过加载之前保存的相同页面自动预热。 通常与innodb_buffer_pool_dump_at_shutdown结合使用。</p><p>增大或减小缓冲池大小时，将以chunk的形式执行操作。chunk大小由innodb_buffer_pool_chunk_size配置选项定义，默认值为128 MB。</p><p>缓冲池大小必须始终等于或者是innodb_buffer_pool_chunk_size * innodb_buffer_pool_instances的倍数。</p><p>如果将缓冲池大小更改为不等于或等于innodb_buffer_pool_chunk_size * innodb_buffer_pool_instances的倍数的值，</p><p>则缓冲池大小将自动调整为等于或者是innodb_buffer_pool_chunk_size * innodb_buffer_pool_instances的倍数的值。</p><p>innodb_buffer_pool_size可以动态设置，允许在不重新启动服务器的情况下调整缓冲池的大小。 可以通过状态变量Innodb_buffer_pool_resize_status报告在线调整缓冲池大小操作的状态。</p><pre class="brush:bash;toolbar:false">mysql>showstatuslike'Innodb_buffer_pool_resize%';
+----------------------------------+-------+
|Variable_name|Value|
+----------------------------------+-------+
|Innodb_buffer_pool_resize_status||
+----------------------------------+-------+</pre><p></p><p>3.2 配置示例</p><p>在以下示例中，innodb_buffer_pool_size设置为3G，innodb_buffer_pool_instances设置为8。innodb_buffer_pool_chunk_size默认值为128M。<br/></p><p>3G是有效的innodb_buffer_pool_size值，因为3G是innodb_buffer_pool_instances = 8 * innodb_buffer_pool_chunk_size = 128M的倍数<br/></p><pre class="brush:bash;toolbar:false">
#mysqld--innodb_buffer_pool_size=3G--innodb_buffer_pool_instances=8&
mysql>showvariableslike'innodb_buffer_pool%';
+-------------------------------------+----------------+
|Variable_name|Value|
+-------------------------------------+----------------+
|innodb_buffer_pool_chunk_size|134217728|
|innodb_buffer_pool_dump_at_shutdown|ON|
|innodb_buffer_pool_dump_now|OFF|
|innodb_buffer_pool_dump_pct|25|
|innodb_buffer_pool_filename|ib_buffer_pool|
|innodb_buffer_pool_instances|8|
|innodb_buffer_pool_load_abort|OFF|
|innodb_buffer_pool_load_at_startup|ON|
|innodb_buffer_pool_load_now|OFF|
|innodb_buffer_pool_size|3221225472|
+-------------------------------------+----------------+
10rowsinset(0.01sec)</pre><p>在以下示例中，innodb_buffer_pool_size设置为3G，innodb_buffer_pool_instances设置为16. innodb_buffer_pool_chunk_size为128M。</p><p>3G不是有效的innodb_buffer_pool_size值，因为3G不是innodb_buffer_pool_instances = 16 * innodb_buffer_pool_chunk_size = 128M的倍数，可以看出innodb_buffer_pool_size的值自动调整到4GB<br/></p><pre class="brush:bash;toolbar:false">
#mysqld--innodb_buffer_pool_size=3G--innodb_buffer_pool_instances=16&
mysql>showvariableslike'%innodb_buffer_pool%';
+-------------------------------------+----------------+
|Variable_name|Value|
+-------------------------------------+----------------+
|innodb_buffer_pool_chunk_size|134217728|
|innodb_buffer_pool_dump_at_shutdown|ON|
|innodb_buffer_pool_dump_now|OFF|
|innodb_buffer_pool_dump_pct|25|
|innodb_buffer_pool_filename|ib_buffer_pool|
|innodb_buffer_pool_instances|16|
|innodb_buffer_pool_load_abort|OFF|
|innodb_buffer_pool_load_at_startup|ON|
|innodb_buffer_pool_load_now|OFF|
|innodb_buffer_pool_size|4294967296|
+-------------------------------------+----------------+
10rowsinset(0.01sec)</pre><p><br/></p><p>3.3 在线调整InnoDB缓冲池大小</p><pre class="brush:bash;toolbar:false">mysql>SETGLOBALinnodb_buffer_pool_size=3221225472</pre><p>3.4 监控在线缓冲池调整进度</p><pre class="brush:bash;toolbar:false">mysql>SHOWSTATUSWHEREVariable_name='InnoDB_buffer_pool_resize_status';
+----------------------------------+----------------------------------------------------+
|Variable_name|Value|
+----------------------------------+----------------------------------------------------+
|Innodb_buffer_pool_resize_status|Completedresizingbufferpoolat18082415:05:03.|
+----------------------------------+----------------------------------------------------+</pre><p>缓冲池大小调整进度也记录在服务器错误日志中。以下为增大时，记录的日志</p><pre class="brush:bash;toolbar:false">2018-08-24T07:05:03.819049Z2[Note]InnoDB:Requestedtoresizebufferpool.(newsize:3221225472bytes)
2018-08-24T07:05:03.819141Z0[Note]InnoDB:Resizingbufferpoolfrom2684354560to3221225472(unit=134217728).
2018-08-24T07:05:03.819155Z0[Note]InnoDB:Disablingadaptivehashindex.
2018-08-24T07:05:03.824902Z0[Note]InnoDB:disabledadaptivehashindex.
2018-08-24T07:05:03.824933Z0[Note]InnoDB:Withdrawingblockstobeshrunken.
2018-08-24T07:05:03.824940Z0[Note]InnoDB:Latchingwholeofbufferpool.
2018-08-24T07:05:03.824959Z0[Note]InnoDB:bufferpool0:resizingwithchunks5to6.
2018-08-24T07:05:03.839564Z0[Note]InnoDB:bufferpool0:1chunks(8192blocks)wereadded.
2018-08-24T07:05:03.839594Z0[Note]InnoDB:bufferpool1:resizingwithchunks5to6.
2018-08-24T07:05:03.848910Z0[Note]InnoDB:bufferpool1:1chunks(8192blocks)wereadded.
2018-08-24T07:05:03.849046Z0[Note]InnoDB:bufferpool2:resizingwithchunks5to6.
2018-08-24T07:05:03.856711Z0[Note]InnoDB:bufferpool2:1chunks(8192blocks)wereadded.
2018-08-24T07:05:03.856741Z0[Note]InnoDB:bufferpool3:resizingwithchunks5to6.
2018-08-24T07:05:03.864867Z0[Note]InnoDB:bufferpool3:1chunks(8192blocks)wereadded.
2018-08-24T07:05:03.864902Z0[Note]InnoDB:Completedtoresizebufferpoolfrom2684354560to3221225472.
2018-08-24T07:05:03.864915Z0[Note]InnoDB:Re-enabledadaptivehashindex.
2018-08-24T07:05:03.864935Z0[Note]InnoDB:Completedresizingbufferpoolat18082415:05:03.</pre><p>以下为减小时，记录的日志</p><pre class="brush:bash;toolbar:false">
2018-08-24T07:10:20.666816Z2[Note]InnoDB:Requestedtoresizebufferpool.(newsize:2684354560bytes)
2018-08-24T07:10:20.666880Z0[Note]InnoDB:Resizingbufferpoolfrom3221225472to2684354560(unit=134217728).
2018-08-24T07:10:20.666889Z0[Note]InnoDB:Disablingadaptivehashindex.
2018-08-24T07:10:20.673416Z0[Note]InnoDB:disabledadaptivehashindex.
2018-08-24T07:10:20.673508Z0[Note]InnoDB:Withdrawingblockstobeshrunken.
2018-08-24T07:10:20.673519Z0[Note]InnoDB:bufferpool0:starttowithdrawthelast8192blocks.
2018-08-24T07:10:20.678441Z0[Note]InnoDB:bufferpool0:withdrawingblocks.(8192/8192)
2018-08-24T07:10:20.678521Z0[Note]InnoDB:bufferpool0:withdrew8192blocksfromfreelist.Triedtorelocate0pages(8192/8192).
2018-08-24T07:10:20.678919Z0[Note]InnoDB:bufferpool0:withdrawntarget8192blocks.
2018-08-24T07:10:20.678977Z0[Note]InnoDB:bufferpool1:starttowithdrawthelast8192blocks.
2018-08-24T07:10:20.681644Z0[Note]InnoDB:bufferpool1:withdrawingblocks.(8192/8192)
2018-08-24T07:10:20.682168Z0[Note]InnoDB:bufferpool1:withdrew8192blocksfromfreelist.Triedtorelocate0pages(8192/8192).
2018-08-24T07:10:20.682235Z0[Note]InnoDB:bufferpool1:withdrawntarget8192blocks.
2018-08-24T07:10:20.682254Z0[Note]InnoDB:bufferpool2:starttowithdrawthelast8192blocks.
2018-08-24T07:10:20.686560Z0[Note]InnoDB:bufferpool2:withdrawingblocks.(8192/8192)
2018-08-24T07:10:20.686917Z0[Note]InnoDB:bufferpool2:withdrew8192blocksfromfreelist.Triedtorelocate0pages(8192/8192).
2018-08-24T07:10:20.687002Z0[Note]InnoDB:bufferpool2:withdrawntarget8192blocks.
2018-08-24T07:10:20.687010Z0[Note]InnoDB:bufferpool3:starttowithdrawthelast8192blocks.
2018-08-24T07:10:20.690038Z0[Note]InnoDB:bufferpool3:withdrawingblocks.(8192/8192)
2018-08-24T07:10:20.690373Z0[Note]InnoDB:bufferpool3:withdrew8192blocksfromfreelist.Triedtorelocate0pages(8192/8192).
2018-08-24T07:10:20.690433Z0[Note]InnoDB:bufferpool3:withdrawntarget8192blocks.
2018-08-24T07:10:20.690479Z0[Note]InnoDB:Latchingwholeofbufferpool.
2018-08-24T07:10:20.690498Z0[Note]InnoDB:bufferpool0:resizingwithchunks6to5.
2018-08-24T07:10:20.693293Z0[Note]InnoDB:bufferpool0:1chunks(8192blocks)werefreed.
2018-08-24T07:10:20.693357Z0[Note]InnoDB:bufferpool1:resizingwithchunks6to5.
2018-08-24T07:10:20.695947Z0[Note]InnoDB:bufferpool1:1chunks(8192blocks)werefreed.
2018-08-24T07:10:20.696011Z0[Note]InnoDB:bufferpool2:resizingwithchunks6to5.
2018-08-24T07:10:20.698977Z0[Note]InnoDB:bufferpool2:1chunks(8192blocks)werefreed.
2018-08-24T07:10:20.699288Z0[Note]InnoDB:bufferpool3:resizingwithchunks6to5.
2018-08-24T07:10:20.702088Z0[Note]InnoDB:bufferpool3:1chunks(8192blocks)werefreed.
2018-08-24T07:10:20.702398Z0[Note]InnoDB:Completedtoresizebufferpoolfrom3221225472to2684354560.
2018-08-24T07:10:20.702413Z0[Note]InnoDB:Re-enabledadaptivehashindex.
2018-08-24T07:10:20.703896Z0[Note]InnoDB:Completedresizingbufferpoolat18082415:10:20.</pre><p></p><p>4. 配置的innodb_buffer_pool_size是否合适？</p><p>当前配置的innodb_buffer_pool_size是否合适，可以通过分析InnoDB缓冲池的性能来验证。</p><p>可以使用以下公式计算InnoDB缓冲池性能：<br/></p><p>Performance = innodb_buffer_pool_reads / innodb_buffer_pool_read_requests * 100<br/></p><p>innodb_buffer_pool_reads：表示InnoDB缓冲池无法满足的请求数。需要从磁盘中读取。<br/></p><p>innodb_buffer_pool_read_requests：表示从内存中读取逻辑的请求数。<br/></p><p>例如，在我的服务器上，检查当前InnoDB缓冲池的性能：</p><pre class="brush:bash;toolbar:false">
root@localhost[(none)]15:35:31>showstatuslike'innodb_buffer_pool_read%';
+---------------------------------------+-------------+
|Variable_name|Value|
+---------------------------------------+-------------+
|Innodb_buffer_pool_read_ahead_rnd|0|
|Innodb_buffer_pool_read_ahead|0|
|Innodb_buffer_pool_read_ahead_evicted|0|
|Innodb_buffer_pool_read_requests|4029033624|
|Innodb_buffer_pool_reads|91661|
+---------------------------------------+-------------+
5rowsinset(0.00sec)
Performance=91661/4029033624*100=0.0022750120389663</pre><p>意味着InnoDB可以满足缓冲池本身的大部分请求。从磁盘完成读取的百分比非常小。因此无需增加innodb_buffer_pool_size值。</p><p>4.1 什么时候减小innodb_buffer_pool_size？</p><p>在专用MySQL服务器上，多余的innodb_buffer内存不会有问题，但是当使用共享服务器时，可能会有性能影响。因为空闲内存对其他程序和操作系统很有用。</p><p>可以使用SHOW ENGINE INNODB STATUS\G命令检查内存状态：</p><pre class="brush:bash;toolbar:false">
mysql>showengineinnodbstatus\G
...
Totallargememoryallocated26386366464
Dictionarymemoryallocated23826297
Bufferpoolsize1572672
Freebuffers8192
Databasepages1553364
Olddatabasepages573246
Modifieddbpages36
Pendingreads0
Pendingwrites:LRU0,flushlist0,singlepage0
Pagesmadeyoung881819,notyoung18198964
0.02youngs/s,0.05non-youngs/s
Pagesread681064,created2749237,written3988300
0.02reads/s,0.12creates/s,11.50writes/s
Bufferpoolhitrate1000/1000,young-makingrate0/1000not0/1000
Pagesreadahead0.00/s,evictedwithoutaccess0.00/s,Randomreadahead0.00/s
LRUlen:1553364,unzip_LRUlen:0
I/Osum[5152]:cur[0],unzipsum[0]:cur[0]
...</pre><p></p><p>Free buffers :表示有多少空闲buffer。如果 此值长时间都较高，则可以考虑减小InnoDB缓冲池大小。</p><p>InnoDB buffer pool 命中率：<br/></p><p>InnoDB buffer pool 命中率 = innodb_buffer_pool_read_requests / (innodb_buffer_pool_read_requests + innodb_buffer_pool_reads ) * 100</p><p>此值低于99%，则可以考虑增加innodb_buffer_pool_size。<br/></p><p>5. InnoDB缓冲池状态变量有哪些？</p><p>可以运行以下命令进行查看：</p><pre class="brush:bash;toolbar:false">
root@localhost[(none)]16:00:31>showglobalstatuslike'%innodb_buffer_pool_pages%';
+----------------------------------+--------+
|Variable_name|Value|
+----------------------------------+--------+
|Innodb_buffer_pool_pages_data|457|
|Innodb_buffer_pool_pages_dirty|0|
|Innodb_buffer_pool_pages_flushed|36|
|Innodb_buffer_pool_pages_free|163363|
|Innodb_buffer_pool_pages_misc|0|
|Innodb_buffer_pool_pages_total|163820|
+----------------------------------+--------+
6rowsinset(0.00sec)</pre><p></p><p>说明：</p><p>Innodb_buffer_pool_pages_data</p><p>InnoDB缓冲池中包含数据的页数。 该数字包括脏页面和干净页面。 使用压缩表时，报告的Innodb_buffer_pool_pages_data值可能大于Innodb_buffer_pool_pages_total（Bug＃59550）。</p><p>Innodb_buffer_pool_pages_dirty</p><p>显示在内存中修改但尚未写入数据文件的InnoDB缓冲池数据页的数量（脏页刷新）。</p><p>Innodb_buffer_pool_pages_flushed</p><p>表示从InnoDB缓冲池中刷新脏页的请求数。</p><p>Innodb_buffer_pool_pages_free</p><p>显示InnoDB缓冲池中的空闲页面</p><p>Innodb_buffer_pool_pages_misc</p><p>InnoDB缓冲池中的页面数量很多，因为它们已被分配用于管理开销，例如行锁或自适应哈希索引。此值也可以计算为Innodb_buffer_pool_pages_total - Innodb_buffer_pool_pages_free - Innodb_buffer_pool_pages_data。</p><p>Innodb_buffer_pool_pages_total</p><p>InnoDB缓冲池的总大小，以page为单位。</p><p>innodb_buffer_pool_reads</p><p>表示InnoDB缓冲池无法满足的请求数。需要从磁盘中读取。</p><p>innodb_buffer_pool_read_requests</p><p>它表示从内存中逻辑读取的请求数。</p><p>innodb_buffer_pool_wait_free</p><p>通常，对InnoDB缓冲池的写入发生在后台。 当InnoDB需要读取或创建页面并且没有可用的干净页面时，InnoDB首先刷新一些脏页并等待该操作完成。 此计数器计算这些等待的实例。 如果已正确设置innodb_buffer_pool_size，则此值应该很小。如果大于0，则表示InnoDb缓冲池太小。</p><p>innodb_buffer_pool_write_request</p><p>表示对缓冲池执行的写入次数。</p><p>6. InnoDB缓冲池当前使用了多少实际GB内存？</p><p>通过将缓冲池中可用的数据与InnoDB页面（InnoDB缓冲池单位）大小相乘，我们可以发现InnoDB缓冲池此时正在使用的实际内存。</p><pre class="brush:bash;toolbar:false">
set@ibpdata=(selectvariable_valuefrominformation_schema.global_statuswherevariable_name='innodb_buffer_pool_pages_data');
ERROR3167(HY000):The'INFORMATION_SCHEMA.GLOBAL_STATUS'featureisdisabled;seethedocumentationfor'show_compatibility_56'
#从MySQL5.7.6开始，GLOBAL_STATUS表中提供的信息从PerformanceSchema获取
mysql>set@ibpdata=(selectvariable_valuefromperformance_schema.global_statuswherevariable_name='innodb_buffer_pool_pages_data');
mysql>select@ibpdata;
+----------+
|@ibpdata|
+----------+
|568|
+----------+
1rowinset(0.00sec)
mysql>set@idbpgsize=(selectvariable_valuefromperformance_schema.global_statuswherevariable_name='innodb_page_size');
mysql>select@idbpgsize;
+------------+
|@idbpgsize|
+------------+
|16384|
+------------+
1rowinset(0.00sec)
mysql>set@ibpsize=@ibpdata*@idbpgsize/(1024*1024*1024);
QueryOK,0rowsaffected(0.00sec)
mysql>select@ibpsize;
+-----------------+
|@ibpsize|
+-----------------+
|0.0086669921875|
+-----------------+
1rowinset(0.00sec)</pre>