扫描调度器：尽管这个名字会使人想起按访问扫描或者实时保护，但其实两者完全不同。
Scan Dispatcher: Although the name may suggest On-access scanning or Real Time Protection, it's nothing like that.
从性能的角度来看，这被认为是一个非常有效的联接操作，因为通过贯穿唯一索引的唯一访问扫描内部表的成本是最优的。
From the performance perspective, this is considered a very efficient join operation, because the cost for scanning the inner table is optimal via unique access through a unique index.
因为其是一个唯一索引扫描，所以在访问路径图中不显示FETCH或表节点。
There is no FETCH or table node shown in the access path graph because it is an index-only scan.
在之前的部分您已经了解了一种类型的访问方法，即索引扫描(IXSCAN)，和一种类型的联接方法，即嵌套循环联接(NLJOIN)。
In the previous section you learned about one type of access method, index scan (IXSCAN), and one type of join method, nested loop join (NLJOIN).
一般来说，索引扫描是访问数据的最有效的方法，尤其是表很大但符合条件的行很少的时候。
Index scans are usually the most efficient way to access data, especially when the table is large but the number of qualified rows is small.
如果应用程序频繁地访问没有适当索引的小表，数据库每次都会把它们装载进内存并扫描它们。
If your application frequently accesses smaller tables without proper indexes, the database will load them into memory each time and scan them.
有了新建的索引，所有表都可以用索引扫描访问。
With the newly created indexes, all tables are accessed with index scans.
是否扫描了整个表或是否由索引访问？
不管数据行是否被提交，以及根据语句的谓词它是否被排除，对于索引扫描和表访问都执行这样的锁定操作。
This locking was done for both index scans and table access whether or not the row of data was committed or whether it would have been excluded based on the statement's predicates.
该选项以筛选的方式用于非匹配索引扫描，且是仅索引访问的一部分。
The option can be used in non matching index scans in a screening fashion and as part of index-only access.
这将允许下面两个查询来使用索引访问，而不是表扫描。
This will allow both of the following queries to use indexed access rather than table scans.
通常情况下，在基础索引提供好处(如唯一索引访问、避免排序或一些类似的好处)时，可通过优化器选择非匹配索引扫描。
Typically, a non-matching index scan is chosen by the optimizer when the underlying index provides benefits such as index-only access, avoids sort, or some similar benefit.
当DB2扫描一个表时，只是访问与那个表相关的段。
When DB2 scans a table, only the segments associated with that table are accessed.
DB 2行压缩功能可以减少磁盘存储需求，同时改进执行全表扫描的大量查询的顺序读取访问。
DB2 row compression features can decrease disk storage requirements while at the same time improve sequential read access of large queries which perform full table scans.
通常情况下，在外部输入的基数显然不小且对于内部表没有一种有效的访问方法时，优化器会选择合并扫描联接。
Typically, the optimizer chooses merge scan join when the cardinality of the outer input is not obviously small and there is no efficient access method for the inner table.
该准则指定一个单一的xml索引扫描，将用于访问给定的表。
This guideline specifies that a single XML index scan be used to access the given table.
用户可访问安全门户来检查其计算机，扫描的结果可以在门户上获得，也可以通过电子邮件获得。
Users access the security portal to check their computers, and they get the results either on the portal or through email.
尽管如此，由于它是主表，而且只用表扫描访问一次，因此会引发一些性能问题，但不会太严重。
However since it is a leading table and will be accessed by the table scan only once, it may cause some performance problems, but it should not be a disaster.
端口探测是一个扫描服务器上所有能访问互联网的可用端口的过程。
Port probing is a process that involves scanning all available ports on your server that are accessible to the Internet.
调优包括添加额外索引来生成一个更高效的访问计划，让表格变幻无常，进而鼓励索引的使用，如果可能的话也可以避免表扫描。
Tuning can include adding extra indexes to yield a more efficient access plan, which makes tables volatile to encourage index usage and avoid table scans if possible.
访问计划指示，强制优化器使用指定的访问方法进行数据检索，要么是连续扫描，要么是索引扫描。
Access plan directives that force the optimizer to use the designated access method for data retrieval, either sequential scan or index scan.
仅扫描索引是未包含表访问的索引访问，因为索引本身包含了所有被请求的数据。
An index only scan is an index access that is not followed by a table access because the index itself contains all the requested data.
顺序扫描一般在决策支持系统(DSS)应用程序中很常见，但很少出现在OLTP访问模式中。
Sequential scans are typical in decision support system (DSS) applications but rare with OLTP access patterns.
通过索引扫描还是表扫描来访问外部表则取决于该表。
The outer table can be accessed by an index scan or by a table scan, depending on the table.
如果注册了那些空间列，那么ArcExplorer将在启动时或者要添加一个新层时访问和扫描那些表。
If they are, then ArcExplorer will access and scan those tables upon startup or when a new layer is to be added.
那么这时可以使用Design Advisor，看看索引是否能导致不需要扫描那么多表的访问计划。
You can use the Design Advisor to see if indexes would result in an access plan with fewer table scans.
要找到所有可用的文章，portlet需要扫描文件系统，这就需要大量的IO访问。
To find all available article the portlet need to scan the filessystem, which requires a lot of IO access.
而且，虽然在type - 2索引扫描中，被删除的行不会被跳过，但是除非同时设置了注册表变量db2_skipdeleted，否则在表扫描访问中，被删除的行将被无条件跳过。
Furthermore, deleted rows are skipped unconditionally on table scan access while deleted keys are not skipped for type-2 index scans unless the registry variable DB2_SKIPDELETED is also set.
在访问路径图中，一个索引扫描通常作为一组四个节点显示在QueryTuner上。
An index scan is typically shown in Query Tuner as a group of four nodes in the access path graph.
该例中，表扫描极其昂贵，因为Informix引擎必须随机地访问数据。
In this case, a table scan is very expensive, because the Informix engine has to access data randomly.
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