http://www.xifenfei.com/2011/12/some-indexes-or-index-subpartitions-of-table-vas-tab_pub_calllog-have-been-marked-unusable.html 1.检查alert日志发现错误 Wed Nov 30 13:36:47 2011 Some indexes or index [sub]partitions of table VAS.TAB_PUB_CALLLOG have been mark…
MySQL :: MySQL 5.7 Reference Manual :: 9.3.1 How MySQL Uses Indexeshttps://dev.mysql.com/doc/refman/5.7/en/mysql-indexes.html CREATE INDEX SELECT COUNT(*) CREATE INDEX windex_countrycode ON sales_rank (countrycode); CREATE INDEX windex_grab_amz_dat…
Create/Drop/Grant/Revoke Roles and Privileges Hive Default Authorization - Legacy Mode has information about these DDL statements: CREATE ROLE GRANT ROLE REVOKE ROLE GRANT privilege_type REVOKE privilege_type DROP ROLE SHOW ROLE GRANT SHOW GRANT For …
转载.节选于 https://dev.mysql.com/doc/refman/8.0/en/innodb-indexes.html This section covers topics related to InnoDB indexes. 1.Clustered and Secondary Indexes Every InnoDB table has a special index called the clustered index where the data for the rows i…
why we need partitions The first and most demanding reason to use partitions in a database is to increase the performance of the database. This is achieved by partition-wise joins; if a user’s queries perform a lot of full-table scans, partitioning w…
摘录自11g的官方文档: UNUSABLE Specify UNUSABLE to mark the index or index partition(s) or index subpartition(s) UNUSABLE. The space allocated for an index or index partition or subpartition is freed immediately when the object is marked UNUSABLE. An unu…
转载.节选于https://dev.mysql.com/doc/refman/8.0/en/innodb-tables.html 1.InnoDB Architecture The following diagram shows in-memory and on-disk structures that comprise the InnoDB storage engine architecture. This section covers topics related to InnoDB tab…
Reference: http://blogs.msdn.com/b/felixmar/archive/2011/08/29/partitioning-amp-archiving-tables-in-sql-server-part-2-split-merge-and-switch-partitions.aspx In the 1st part of this post, I explained how to create a partitioned table using a partition…
Index Seek是Sql Server执行查询语句时利用建立的索引进行查找,索引是B树结构,Sql Server先查找索引树的根节点,一级一级向下查找,在查找到相应叶子节点后,取出叶子节点的数据.对于聚集索引,叶子节点是整个表的数据,能够获取到所有列的数据,而对于非聚集索引,叶子节点存储的是索引列的数据,如果索引有包含列,那么叶子节点中存储有包含列的数据,获取的数据是索引列和包含列,如果还需要其他列的数据,那么必须进行key lookup,根据索引叶子节点包含的“行地址”信息到源表中去获取数…
深入理解 index merge 是使用索引进行优化的重要基础之一.理解了 index merge 技术,我们才知道应该如何在表上建立索引. 1. 为什么会有index merge 我们的 where 中可能有多个条件(或者join)涉及到多个字段,它们之间进行 AND 或者 OR,那么此时就有可能会使用到 index merge 技术.index merge 技术如果简单的说,其实就是:对多个索引分别进行条件扫描,然后将它们各自的结果进行合并(intersect/union). MySQL5.…
A clustered index determines the order in which the rows of a table are stored on disk. If a table has a clustered index, then the rows of that table will be stored on disk in the same exact order as the clustered index. An example will help clarify…
An index is used to speed up searching in the database. By default, when you create this table, your data will be stored on disk and sorted by the "Id" primary key column. This default sort is called the "Clustered Index". Affects the…
CREATE INDEX windex_countrycode ON sales_rank (countrycode); CREATE INDEX windex_grab_amz_date ON sales_rank (grab_amz_date); CREATE INDEX windex_categoryid ON sales_rank (categoryid); CREATE INDEX windex_grab_rank ON sales_rank (grab_rank); [SQL] CR…
warehouse_db=# create table item (item_id integer not null,item_name text,item_price numeric,item_data text);CREATE TABLEwarehouse_db=# create index item_idx on item(item_id);CREATE INDEX warehouse_db=# \di item_idx List of relations Schema | Name |…
Understanding the B-tree and hash data structures can help predict how different queries perform on different storage engines that use these data structures in their indexes, particularly for theMEMORY storage engine that lets you choose B-tree or ha…
A key is a column or expression on which you can build an index. Follow these guidelines for choosing keys to index: Consider indexing keys that are used frequently in WHERE clauses. Consider indexing keys that are used frequently to join tables in S…
