MySQL 上的 0.07 秒查询在 MariaDB 上需要 11.68 秒？
0.07s query on MySQL takes 11.68s on MariaDB?
涉及不同的硬件（MySQL 在我的笔记本电脑上，MariaDB 在服务器上）但通常差异最多是 2 倍而不是 166 倍！
这些表在每个实例上包含相同的数据（_cache_card 中有 18,000 行，card_legality 中有 157,000 行）。
查询
SELECT * FROM _cache_card AS c
WHERE c.id IN (SELECT card_id FROM card_legality WHERE format_id = 35);
解释
MariaDB:
+------+--------------+---------------+------+---------------------------------+-----------+---------+-------+-------+-------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+--------------+---------------+------+---------------------------------+-----------+---------+-------+-------+-------------------------------------------------+
| 1 | PRIMARY | <subquery2> | ALL | distinct_key | NULL | NULL | NULL | 9414 | |
| 1 | PRIMARY | c | ALL | NULL | NULL | NULL | NULL | 18567 | Using where; Using join buffer (flat, BNL join) |
| 2 | MATERIALIZED | card_legality | ref | format_id,idx_card_id_format_id | format_id | 4 | const | 9414 | |
+------+--------------+---------------+------+---------------------------------+-----------+---------+-------+-------+-------------------------------------------------+
MySQL:
+----+--------------+---------------+------------+--------+---------------------------------+------------+---------+------------+-------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+--------------+---------------+------------+--------+---------------------------------+------------+---------+------------+-------+----------+-------------+
| 1 | SIMPLE | c | NULL | ALL | NULL | NULL | NULL | NULL | 18055 | 100.00 | Using where |
| 1 | SIMPLE | <subquery2> | NULL | eq_ref | <auto_key> | <auto_key> | 4 | cards.c.id | 1 | 100.00 | NULL |
| 2 | MATERIALIZED | card_legality | NULL | ref | format_id,idx_card_id_format_id | format_id | 4 | const | 37828 | 100.00 | NULL |
+----+--------------+---------------+------------+--------+---------------------------------+------------+---------+------------+-------+----------+-------------+
创建TABLE
两者：
CREATE TABLE `card_legality` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`card_id` int(11) NOT NULL,
`format_id` int(11) NOT NULL,
`legality` varchar(190) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `format_id` (`format_id`),
KEY `idx_card_id_format_id` (`card_id`,`format_id`,`legality`),
CONSTRAINT `card_legality_ibfk_1` FOREIGN KEY (`card_id`) REFERENCES `card` (`id`),
CONSTRAINT `card_legality_ibfk_2` FOREIGN KEY (`format_id`) REFERENCES `format` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1190863 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
（此处的输出是逐个字符相同的。）
MariaDB:
CREATE TABLE `_cache_card` (
`id` int(11) NOT NULL DEFAULT 0,
`layout` varchar(190) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
`face_id` int(11) NOT NULL DEFAULT 0,
`name` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`mana_cost` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`cmc` double DEFAULT NULL,
`power` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`toughness` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`loyalty` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`type` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`text` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`search_text` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`image_name` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`hand` mediumtext DEFAULT NULL,
`life` mediumtext DEFAULT NULL,
`starter` mediumtext DEFAULT NULL,
`position` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`name_ascii` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`card_id` mediumtext DEFAULT NULL,
`names` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`legalities` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`pd_legal` int(1) DEFAULT NULL,
`bugs` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
KEY `idx_name_name` (`name`(142))
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
MySQL:
CREATE TABLE `_cache_card` (
`id` int(11) NOT NULL DEFAULT '0',
`layout` varchar(190) COLLATE utf8mb4_unicode_ci NOT NULL,
`face_id` int(11) NOT NULL DEFAULT '0',
`name` longtext COLLATE utf8mb4_unicode_ci,
`mana_cost` mediumtext COLLATE utf8mb4_unicode_ci,
`cmc` double DEFAULT NULL,
`power` mediumtext COLLATE utf8mb4_unicode_ci,
`toughness` mediumtext COLLATE utf8mb4_unicode_ci,
`loyalty` mediumtext COLLATE utf8mb4_unicode_ci,
`type` longtext COLLATE utf8mb4_unicode_ci,
`text` mediumtext COLLATE utf8mb4_unicode_ci,
`search_text` mediumtext COLLATE utf8mb4_unicode_ci,
`image_name` mediumtext COLLATE utf8mb4_unicode_ci,
`hand` mediumtext CHARACTER SET utf8mb4,
`life` mediumtext CHARACTER SET utf8mb4,
`starter` mediumtext CHARACTER SET utf8mb4,
`position` mediumtext COLLATE utf8mb4_unicode_ci,
`name_ascii` longtext COLLATE utf8mb4_unicode_ci,
`card_id` mediumtext CHARACTER SET utf8mb4,
`names` mediumtext COLLATE utf8mb4_unicode_ci,
`legalities` mediumtext COLLATE utf8mb4_unicode_ci,
`pd_legal` int(1) DEFAULT NULL,
`bugs` mediumtext COLLATE utf8mb4_unicode_ci,
KEY `idx_name_name` (`name`(142))
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
其他详细信息
MariaDB:
version=10.2.16-MariaDB
optimizer_switch=index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on
MySQL:
version=5.7.17
optimizer_switch=index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=on,mrr=on,mrr_cost_based=on,block_nested_loop=on,batched_key_access=off,materialization=on,semijoin=on,loosescan=on,firstmatch=on,duplicateweedout=on,subquery_materialization_cost_based=on,use_index_extensions=on,condition_fanout_filter=on,derived_merge=on
在 card_legality(format_id,card_id)
上添加索引
这不知何故使事情变得变慢。
CREATE INDEX idx_format_id_card_id ON card_legality(format_id,card_id);
现在超过 15 秒。
EXPLAIN（在 MariaDB 上）说：
+------+--------------+---------------+------+---------------------------------------------+-----------------------+---------+-------+-------+-------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+--------------+---------------+------+---------------------------------------------+-----------------------+---------+-------+-------+-------------------------------------------------+
| 1 | PRIMARY | <subquery2> | ALL | distinct_key | NULL | NULL | NULL | 16942 | |
| 1 | PRIMARY | c | ALL | NULL | NULL | NULL | NULL | 17653 | Using where; Using join buffer (flat, BNL join) |
| 2 | MATERIALIZED | card_legality | ref | idx_card_id_format_id,idx_format_id_card_id | idx_format_id_card_id | 4 | const | 16942 | Using index |
+------+--------------+---------------+------+---------------------------------------------+-----------------------+---------+-------+-------+-------------------------------------------------+
我要添加索引：
CREATE INDEX idx_name ON card_legality(format_id, card_id);
SELECT *
FROM _cache_card AS c
WHERE c.id IN (SELECT card_id FROM card_legality WHERE format_id = 35);
-- covering index created before
IN 从优化的角度来看可能很棘手。我想知道这是否在两个系统上效果更好：
SELECT c.*
FROM _cache_card c
WHERE EXISTS (SELECT 1
FROM card_legality cl
WHERE cl.card_id = c.id AND format_id = 35
);
目前还不清楚为什么 MariaDB 目前使用这个次优的执行计划。它可能假设您的数据分布有问题（尽管我不确定在哪种情况下这将是最佳计划）。使用 optimize table card_legality, _cache_card; 修复统计数据可能会有所帮助。
如果没有，并且由于我们在评论中确定 (card_id,format_id) 是唯一的，我会尝试添加以下索引
CREATE UNIQUE INDEX uidx_card_legality ON card_legality(format_id, card_id)
并使用
SELECT c.*
FROM _cache_card AS c
JOIN card_legality l FORCE INDEX (uidx_card_legality)
ON l.card_id = c.id AND l.format_id = 35;
这基本上是 MySQL 当前执行您的查询的方式（同时动态创建此索引），尽管您似乎已经尝试过使用 Lukasz 的答案创建该索引但没有成功。
您应该删除 force index（这只是为了绝对确保 MariaDB 没有回旋余地来做其他事情）并检查 MariaDB/MySQL 是否仍在使用它。还要测试 format_id 的其他值会发生什么，因为 35 可能是异常值（例如，您可能只有少数该格式的条目），为此优化执行计划可能会减慢查询所有其他值。当然，请确保您正在比较相似的结果集，就好像 MariaDB 有例如格式 35 有 10k 个条目，而 MySQL 有 none，这不是一场公平的战斗。
差异的原因始于 MySQL 5.6 和 MariaDB 10.0 的出现——它们 分别 开发了几个改进的优化。您遇到了一个涉及 IN 的构造，其中一个做出了另一个没有（可能还没有）拾取的重大改进。
只要 JOIN 可行，就避免 IN ( SELECT ... )。
EXISTS( SELECT 1 ... ) 是另一个可以试验的结构。
索引：
PRIMARY KEY on every table !
card_legality: INDEX(format_id, card_id) -- in this order
_cache_card: (id) -- This seems like a serious omission !
一些会影响性能的事情：使用 *TEXT 而较小的 VARCHAR 就足够了。
计时时，运行查询两次。第一个将内容复制到 RAM (buffer_pool)；第二个比较现实。
多少内存？每个 innodb_buffer_pool_size 的值是多少？
涉及不同的硬件（MySQL 在我的笔记本电脑上，MariaDB 在服务器上）但通常差异最多是 2 倍而不是 166 倍！
这些表在每个实例上包含相同的数据（_cache_card 中有 18,000 行，card_legality 中有 157,000 行）。
查询
SELECT * FROM _cache_card AS c
WHERE c.id IN (SELECT card_id FROM card_legality WHERE format_id = 35);
解释
MariaDB:
+------+--------------+---------------+------+---------------------------------+-----------+---------+-------+-------+-------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+--------------+---------------+------+---------------------------------+-----------+---------+-------+-------+-------------------------------------------------+
| 1 | PRIMARY | <subquery2> | ALL | distinct_key | NULL | NULL | NULL | 9414 | |
| 1 | PRIMARY | c | ALL | NULL | NULL | NULL | NULL | 18567 | Using where; Using join buffer (flat, BNL join) |
| 2 | MATERIALIZED | card_legality | ref | format_id,idx_card_id_format_id | format_id | 4 | const | 9414 | |
+------+--------------+---------------+------+---------------------------------+-----------+---------+-------+-------+-------------------------------------------------+
MySQL:
+----+--------------+---------------+------------+--------+---------------------------------+------------+---------+------------+-------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+--------------+---------------+------------+--------+---------------------------------+------------+---------+------------+-------+----------+-------------+
| 1 | SIMPLE | c | NULL | ALL | NULL | NULL | NULL | NULL | 18055 | 100.00 | Using where |
| 1 | SIMPLE | <subquery2> | NULL | eq_ref | <auto_key> | <auto_key> | 4 | cards.c.id | 1 | 100.00 | NULL |
| 2 | MATERIALIZED | card_legality | NULL | ref | format_id,idx_card_id_format_id | format_id | 4 | const | 37828 | 100.00 | NULL |
+----+--------------+---------------+------------+--------+---------------------------------+------------+---------+------------+-------+----------+-------------+
创建TABLE
两者：
CREATE TABLE `card_legality` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`card_id` int(11) NOT NULL,
`format_id` int(11) NOT NULL,
`legality` varchar(190) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `format_id` (`format_id`),
KEY `idx_card_id_format_id` (`card_id`,`format_id`,`legality`),
CONSTRAINT `card_legality_ibfk_1` FOREIGN KEY (`card_id`) REFERENCES `card` (`id`),
CONSTRAINT `card_legality_ibfk_2` FOREIGN KEY (`format_id`) REFERENCES `format` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1190863 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
（此处的输出是逐个字符相同的。）
MariaDB:
CREATE TABLE `_cache_card` (
`id` int(11) NOT NULL DEFAULT 0,
`layout` varchar(190) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
`face_id` int(11) NOT NULL DEFAULT 0,
`name` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`mana_cost` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`cmc` double DEFAULT NULL,
`power` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`toughness` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`loyalty` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`type` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`text` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`search_text` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`image_name` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`hand` mediumtext DEFAULT NULL,
`life` mediumtext DEFAULT NULL,
`starter` mediumtext DEFAULT NULL,
`position` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`name_ascii` longtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`card_id` mediumtext DEFAULT NULL,
`names` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`legalities` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
`pd_legal` int(1) DEFAULT NULL,
`bugs` mediumtext CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,
KEY `idx_name_name` (`name`(142))
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
MySQL:
CREATE TABLE `_cache_card` (
`id` int(11) NOT NULL DEFAULT '0',
`layout` varchar(190) COLLATE utf8mb4_unicode_ci NOT NULL,
`face_id` int(11) NOT NULL DEFAULT '0',
`name` longtext COLLATE utf8mb4_unicode_ci,
`mana_cost` mediumtext COLLATE utf8mb4_unicode_ci,
`cmc` double DEFAULT NULL,
`power` mediumtext COLLATE utf8mb4_unicode_ci,
`toughness` mediumtext COLLATE utf8mb4_unicode_ci,
`loyalty` mediumtext COLLATE utf8mb4_unicode_ci,
`type` longtext COLLATE utf8mb4_unicode_ci,
`text` mediumtext COLLATE utf8mb4_unicode_ci,
`search_text` mediumtext COLLATE utf8mb4_unicode_ci,
`image_name` mediumtext COLLATE utf8mb4_unicode_ci,
`hand` mediumtext CHARACTER SET utf8mb4,
`life` mediumtext CHARACTER SET utf8mb4,
`starter` mediumtext CHARACTER SET utf8mb4,
`position` mediumtext COLLATE utf8mb4_unicode_ci,
`name_ascii` longtext COLLATE utf8mb4_unicode_ci,
`card_id` mediumtext CHARACTER SET utf8mb4,
`names` mediumtext COLLATE utf8mb4_unicode_ci,
`legalities` mediumtext COLLATE utf8mb4_unicode_ci,
`pd_legal` int(1) DEFAULT NULL,
`bugs` mediumtext COLLATE utf8mb4_unicode_ci,
KEY `idx_name_name` (`name`(142))
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
其他详细信息
MariaDB:
version=10.2.16-MariaDB
optimizer_switch=index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,index_merge_sort_intersection=off,engine_condition_pushdown=off,index_condition_pushdown=on,derived_merge=on,derived_with_keys=on,firstmatch=on,loosescan=on,materialization=on,in_to_exists=on,semijoin=on,partial_match_rowid_merge=on,partial_match_table_scan=on,subquery_cache=on,mrr=off,mrr_cost_based=off,mrr_sort_keys=off,outer_join_with_cache=on,semijoin_with_cache=on,join_cache_incremental=on,join_cache_hashed=on,join_cache_bka=on,optimize_join_buffer_size=off,table_elimination=on,extended_keys=on,exists_to_in=on,orderby_uses_equalities=on,condition_pushdown_for_derived=on
MySQL:
version=5.7.17
optimizer_switch=index_merge=on,index_merge_union=on,index_merge_sort_union=on,index_merge_intersection=on,engine_condition_pushdown=on,index_condition_pushdown=on,mrr=on,mrr_cost_based=on,block_nested_loop=on,batched_key_access=off,materialization=on,semijoin=on,loosescan=on,firstmatch=on,duplicateweedout=on,subquery_materialization_cost_based=on,use_index_extensions=on,condition_fanout_filter=on,derived_merge=on
在 card_legality(format_id,card_id)
上添加索引这不知何故使事情变得变慢。
CREATE INDEX idx_format_id_card_id ON card_legality(format_id,card_id);
现在超过 15 秒。
EXPLAIN（在 MariaDB 上）说：
+------+--------------+---------------+------+---------------------------------------------+-----------------------+---------+-------+-------+-------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+--------------+---------------+------+---------------------------------------------+-----------------------+---------+-------+-------+-------------------------------------------------+
| 1 | PRIMARY | <subquery2> | ALL | distinct_key | NULL | NULL | NULL | 16942 | |
| 1 | PRIMARY | c | ALL | NULL | NULL | NULL | NULL | 17653 | Using where; Using join buffer (flat, BNL join) |
| 2 | MATERIALIZED | card_legality | ref | idx_card_id_format_id,idx_format_id_card_id | idx_format_id_card_id | 4 | const | 16942 | Using index |
+------+--------------+---------------+------+---------------------------------------------+-----------------------+---------+-------+-------+-------------------------------------------------+
我要添加索引：
CREATE INDEX idx_name ON card_legality(format_id, card_id);
SELECT *
FROM _cache_card AS c
WHERE c.id IN (SELECT card_id FROM card_legality WHERE format_id = 35);
-- covering index created before
IN 从优化的角度来看可能很棘手。我想知道这是否在两个系统上效果更好：
SELECT c.*
FROM _cache_card c
WHERE EXISTS (SELECT 1
FROM card_legality cl
WHERE cl.card_id = c.id AND format_id = 35
);
目前还不清楚为什么 MariaDB 目前使用这个次优的执行计划。它可能假设您的数据分布有问题（尽管我不确定在哪种情况下这将是最佳计划）。使用 optimize table card_legality, _cache_card; 修复统计数据可能会有所帮助。
如果没有，并且由于我们在评论中确定 (card_id,format_id) 是唯一的，我会尝试添加以下索引
CREATE UNIQUE INDEX uidx_card_legality ON card_legality(format_id, card_id)
并使用
SELECT c.*
FROM _cache_card AS c
JOIN card_legality l FORCE INDEX (uidx_card_legality)
ON l.card_id = c.id AND l.format_id = 35;
这基本上是 MySQL 当前执行您的查询的方式（同时动态创建此索引），尽管您似乎已经尝试过使用 Lukasz 的答案创建该索引但没有成功。
您应该删除 force index（这只是为了绝对确保 MariaDB 没有回旋余地来做其他事情）并检查 MariaDB/MySQL 是否仍在使用它。还要测试 format_id 的其他值会发生什么，因为 35 可能是异常值（例如，您可能只有少数该格式的条目），为此优化执行计划可能会减慢查询所有其他值。当然，请确保您正在比较相似的结果集，就好像 MariaDB 有例如格式 35 有 10k 个条目，而 MySQL 有 none，这不是一场公平的战斗。
差异的原因始于 MySQL 5.6 和 MariaDB 10.0 的出现——它们 分别 开发了几个改进的优化。您遇到了一个涉及 IN 的构造，其中一个做出了另一个没有（可能还没有）拾取的重大改进。
只要 JOIN 可行，就避免 IN ( SELECT ... )。
EXISTS( SELECT 1 ... ) 是另一个可以试验的结构。
索引：
PRIMARY KEY on every table !
card_legality: INDEX(format_id, card_id) -- in this order
_cache_card: (id) -- This seems like a serious omission !
一些会影响性能的事情：使用 *TEXT 而较小的 VARCHAR 就足够了。
计时时，运行查询两次。第一个将内容复制到 RAM (buffer_pool)；第二个比较现实。
多少内存？每个 innodb_buffer_pool_size 的值是多少？