當單表達到幾千萬時，查詢一次要很久，如果有聯合查詢，有可能會死在那
分庫分表主要就是解決這個問題，減小數據庫的負擔，縮短查詢時間

分庫：
1）按功能分
用戶類庫、商品類庫、訂單類庫、日志類、統計類庫...
1）按地區分
每個城市或省市一個同樣的庫，加上后綴或前綴如：db_click_bj、db_click_sh...

分表：
1、橫向分表 解決表記錄太大問題
1）按某個字段分，
如：discuz的附件表分成10個附件分表pre_forum_attachment_0到pre_forum_attachment_9，還有1個附件索引表pre_forum_attachment存儲tid和附件id關系
根據主題的tid最后一位來決定附件要保存在哪個分表，
2）按日期分表
一些日志、統計類的可以按年、月、日、周分表
如：點擊量統計click_201601、click_201602
3）使用mysql的merge
先把分表創建好，然后創建總表指定engine= MERGE UNION=(table1,table2) INSERT_METHOD = LAST;

2、縱向分表 解決列過多問題
1）經常組合查詢的列放在一個表，常用字段的表可考慮Memory引擎
2）不經常使用的字段單獨成表
3）把text、blob等大字段拆分放在附表
如：phpcms的文章表分成主表v9_news和從表v9_news_data，主表存標題、關鍵字、瀏覽量等，從表存具體內容、模板等

很多主流mvc框架都提供了切換數據庫訪問方法

thinkphp切換數據庫

$this->db(1,"mysql://root:123456@localhost:3306/test")->query("查詢sql");//數據庫連接信息可放在配置文件
$this->db(1)->query("查詢sql");//下次直接使用編號1定位

分表的話 在查詢前先根據分表規則把表名查出

這里用兩臺機子簡單以同個業務庫分庫，同個表分表，演示插入、查詢如何定位庫和表并最終成功執行

兩臺機子：

server1：192.168.1.198

server2：192.168.1.199

兩臺機子都執行下面操作

1、先創建10個數據庫，每個數據庫10個表

當然也可以改成百庫百表，也可手動創建，我為了方便寫了個腳本批量創建

create.php
[php]?view plaincopy

<?php??

ini_set('memory_limit',?'-1');??

$con=mysql_connect("192.168.1.198","open","123456");??

if($con){?????

????for($i=0;$i<10;$i++){//10個庫??

????????$sql="drop?database?cloude_{$i};";//刪庫?謹慎??

????????mysql_query($sql);??

????????$sql="create?database?cloude_{$i}?default?character?set?utf8?collate?utf8_general_ci;";??

????????$do=mysql_query($sql,$con)or?die(mysql_error());??

????????if($do){??

????????????mysql_select_db("cloude_{$i}",$con);??

????????????mysql_query("set?name?gtf8");??

????????????for($j=0;$j<10;$j++){????????//10個表??

????????????????$sql="drop?table?if?exists?user_{$j};";??

????????????????mysql_query($sql);??

????????????????$sql="create?table?user_{$j}??

????????????????(??

????????????????????id?char(36)?not?null?primary?key,??

????????????????????name?char(15)?not?null?default?'',??

????????????????????password?char(32)?not?null?default?'',??

????????????????????sex?char(1)?not?null?default?'男'??

????????????????)engine=InnoDB;";??

????????????????$do=mysql_query($sql,$con)?or?die(mysql_error());??

????????????????if($do){??

????????????????????//echo?"create?table?user_{$j}?successful!?<br/>";??

????????????????}else{??

????????????????????//echo?"create?error!";??

????????????????}??

????????????}??

????????}??

????}??

}else{??

????echo?"connect?error!!!!";??

}??

2、分庫分表路由實現

Config.PHP

[php]?view plaincopy

<?php??

class?Config{????

????public?$dsn;????

????public?$user;????

????public?$password;????

????public?$dbname;?//分庫分表后得到的數據庫名??

????public?$table;?//分庫分表后得到的表名??

????private?static?$config;//mysql配置數組??

????private?static?$configFile?=?'mysql.php';?//配置文件路徑???

??????

????public?function?__construct($dbname,?$table,?$id?=?0){????

????????if?(is_null(static::$config))?{????

????????????$config?=?include(static::$configFile);????

????????????static::$config?=?$config;????

????????}????

??????

????????$config?=?static::$config;????

????????if?(isset($config['shared'])?&&?isset($config['shared'][$dbname]))?{????

????????????$dbconfig?=?$config['shared'][$dbname];????

????????????$id?=?is_numeric($id)???(int)$id?:?crc32($id);????

????????????$database_id?=?($id?/?$dbconfig['database_split'][0])?%?$dbconfig['database_split'][1];????

????????????$table_id?=?($id?/?$dbconfig['table_split'][0])?%?$dbconfig['table_split'][1];????

??????

????????????foreach?($dbconfig['host']?as?$key?=>?$conf)?{????

????????????????list($from,?$to)?=?explode('-',?$key);????

????????????????if?($from?<=?$database_id?&&?$database_id?<=?$to)?{????

????????????????????$the_config?=?$conf;????

????????????????}????

????????????}????

??????

????????????$this->dbname?=?$dbname?.?'_'?.?$database_id;????

????????????$this->table?=?$table?.?'_'?.?$table_id;????

????????}?else?{????

????????????$this->dbname?=?$dbname;????

????????????$this->table?=?$table;????

????????????$the_config?=?$config['db'][$dbname];????

????????}????

????????$c?=?$the_config;????

????????if?(isset($c['unix_socket'])?&&?$c['unix_socket'])?{????

????????????$this->dsn?=?sprintf('mysql:dbname=%s;unix_socket=%s',?$this->dbname,?$c['unix_socket']);????

????????}?else?{????

????????????$this->dsn?=?sprintf('mysql:dbname=%s;host=%s;port=%s',?$this->dbname,?$c['host'],?$c['port']);????

????????}????

????????$this->user?=?$c['user'];????

????????$this->password?=?$c['password'];????

????}????

??????

}??

3、數據庫配置文件
mysql.php
[php]?view plaincopy

<?php??

$default?=?array(????

????'unix_socket'?=>?null,????

????'host'?=>?'192.168.1.198',????

????'port'?=>?'3306',????

????'user'?=>?'open',????

????'password'?=>?'123456',????

);????

$db_199?=?array(????

????'unix_socket'?=>?null,????

????'host'?=>?'192.168.1.199',????

????'port'?=>?'3306',????

????'user'?=>?'open',????

????'password'?=>?'123456',????

);???????

$config?=?array(????

????//?不進行分庫分表的數據庫????

????'db'?=>?array(????

????????'hadoop'?=>?$default,????

????),????

????//?分庫分表????

????'shared'?=>?array(????

????????'cloude'?=>?array(????

????????????'host'?=>?array(????

????????????????/**??

?????????????????*?編號為?0?到?4?的庫使用的鏈接配置??

?????????????????*/???

????????????????'0-4'?=>?$default,????

????????????????/**??

?????????????????*?編號為?5?到?9?的庫使用的鏈接配置??

?????????????????*/???

????????????????'5-9'?=>?$db_199,?????

??????

????????????),????

??????

????????????//?分庫分表規則????

????????????/**??

?????????????*?下面的配置對應10庫10表?

?????????????*?如果根據?uid?進行分表，假設?uid?為?224，對應的庫表為：??

?????????????*??(224?/?1)?%?10?=?4?為編號為?4?的庫??

?????????????*??(224?/?10)?%?10?=?1?為編號為?2?的表??

?????????????*/???

????????????'database_split'?=>?array(1,?10),????

????????????'table_split'?=>?array(10,?10),????

????????),????

????),????

);????

return?$config;??

4、模型類操作數據庫

Model.PHP

[php]?view plaincopy

<?php??

require_once?'Config.php';//引入配置信息??

class?Model{????

????public?$config;?????//數據庫配置??

????public?$connection;?//pdo??

????protected?$dbnamePrefix;?//庫前綴如cloude_50?前綴為cloude???

????protected?$tablePrefix;??//表前綴??

????protected?$dbname;??//分庫分表后對應的庫??

????protected?$table;???//分庫分表后對應的庫表??

??????

????public?function?__construct($id){????

????????$this->config?=?new?Config($this->dbnamePrefix,?$this->tablePrefix,?$id);??????????????????//根據id找到對應庫和表??

????????$this->connection?=?new?Pdo($this->config->dsn,?$this->config->user,?$this->config->password);//實例化pdo????

????????$this->connection->exec("set?names?utf8");?????

????????$this->dbname?=?$this->config->dbname;??

????????$this->table?=?$this->config->table;????

????}????

??????

????public?function?update(array?$data,?array?$where?=?array()){????

??????

????}????

??????

????public?function?select(array?$condition){???

????????$sqlwhere='';??

????????if(!empty($condition)){?????

????????????foreach?($condition?as?$field?=>?$value)?{????

????????????????$where[]?=?'`'.$field.'`='."'".addslashes($value)."'";????

????????????}????

????????????$sqlwhere?.=?'?'.implode('?and?',?$where);?????

????????}??

????????$sql="select?*?from?".$this->dbname.'.'.$this->table;??

????????if($sqlwhere){??

????????????$sql.="?where?$sqlwhere";??

????????}??

????????$res=$this->connection->query($sql);??

????????$data['data']=$res->fetchAll(PDO::FETCH_ASSOC);??

????????$data['info']=array("dsn"=>$this->config->dsn,"dbname"=>$this->dbname,"table"=>$this->table,"sql"=>$sql);??

????????return?$data;?????

????}????

????public?function?insert(array?$arrData)?{??

????????$name?=?$values?=?'';??

????????$flag?=?$flagV?=?1;??

????????$true?=?is_array(?current($arrData)?);//判斷是否一次插入多條數據??

????????if($true)?{??

????????????//構建插入多條數據的sql語句??

????????????foreach($arrData?as?$arr)?{??

????????????????$values?.=?$flag???'('?:?',(';??

????????????????foreach($arr?as?$key?=>?$value)?{??

????????????????????if($flagV)?{??

????????????????????????if($flag)?$name?.=?"$key";??

????????????????????????$values?.=?"'$value'";??

????????????????????????$flagV?=?0;??

????????????????????}?else?{??

????????????????????????if($flag)?$name?.=?",$key";??

????????????????????????$values?.=?",'$value'";??

????????????????????}??

????????????????}??

????????????????$values?.=?')?';??

????????????????$flag?=?0;??

????????????????$flagV?=?1;??

????????????}??

????????}?else?{??

????????????//構建插入單條數據的sql語句??

????????????foreach($arrData?as?$key?=>?$value)?{??

????????????????if($flagV)?{??

????????????????????$name?=?"$key";??

????????????????????$values?=?"('$value'";??

????????????????????$flagV?=?0;??

????????????????}?else?{??

????????????????????$name?.=?",$key";??

????????????????????$values?.=?",'$value'";??

????????????????}??

????????????}??

????????????$values?.=?")?";??

????????}??

???????????

????????$sql?=?"insert?into?".$this->dbname.'.'.$this->table."?($name)?values?$values";??

????????if(?($rs?=?$this->connection->exec($sql)?)?>?0?)?{??

????????????return?array("dsn"=>$this->config->dsn,"dbname"=>$this->dbname,"table"=>$this->table,"sql"=>$sql);??

????????}??

????????return?false;??

????}??

????public?function?query($sql){????

????????return?$this->connection->query($sql);????

????}????

}??

5、測試

使用主鍵id作為分表字段，那最好就不要使用自增了，可使用uuid

User.php

[php]?view plaincopy

<?php??

require?'Config.php';????

require?'Model.php';????

class?User?extends?Model????

{????

????protected?$dbnamePrefix?=?'cloude';????

????protected?$tablePrefix?=?'user';????

}???

//生成唯一uuid??

function?create_uuid($prefix?=?""){????//可以指定前綴??

????$str?=?md5(uniqid(mt_rand(),?true));?????

????$uuid??=?substr($str,0,8)?.?'-';?????

????$uuid?.=?substr($str,8,4)?.?'-';?????

????$uuid?.=?substr($str,12,4)?.?'-';?????

????$uuid?.=?substr($str,16,4)?.?'-';?????

????$uuid?.=?substr($str,20,12);?????

????return?$prefix?.?$uuid;??

}??

??

$userId=create_uuid();??

$user?=?new?User($userId);??

$data=array('id'=>$userId,'name'=>'大明'.$userId,'password'=>'14e1b600b1fd579f47433b88e8d85291','sex'=>'男');????

if($result=$user->insert($data)){??

????echo?'插入成功：','<pre/>';??

????print_r($result);??

}??

??

$condition=array("id"=>$userId);??

$list=$user->select($condition);??

if($list){??

????echo?'查詢成功：','<pre/>';??

????print_r($list);??

}??

6、結果
插入成功會返回插入到哪個庫哪個表，查詢成功返回從哪個庫哪個表查的

分庫分表注意事項：
1、維度問題
假如用戶購買了商品,需 要將交易記錄保存取來，如果按照用戶的緯度分表，則每個用戶的交易記錄都保存在同一表中，所以很快很方便的查找到某用戶的購買情況，但是某商品被購買的情 況則很有可能分布在多張表中，查找起來比較麻煩。反之，按照商品維度分表，可以很方便的查找到此商品的購買情況，但要查找到買人的交易記錄比較麻煩。
所以常見的解決方式有：
通過掃表的方式解決，此方法基本不可能，效率太低了。
記錄兩份數據，一份按照用戶緯度分表，一份按照商品維度分表。
通過搜索引擎解決，但如果實時性要求很高，又得關系到實時搜索
2、避免分表join操作 因為關聯的表有可能不在同一數據庫中
3、避免跨庫事務
避免在一個事務中修改db0中的表的時候同時修改db1中的表，一個是操作起來更復雜，效率也會有一定影響
4、分表宜多不宜少；這樣做主要是為了盡量避免后期可能遇到的二次拆分
5、盡量把同一組數據放到同一DB服務器上

例如將賣家a的商品和交易信息都放到db0中，當db1掛了的時候，賣家a相關的東西可以正常使用。也就是說避免數據庫中的數據依賴另一數據庫中的數據

文章來源http://blog.csdn.NET/nuli888/article/details/52143065

來源:http://blog.csdn.net/weixin_29778143/article/details/72236453

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