Partition Table 查询性能

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分区表的高效的查询性能是基于Partition Elimination 和 Partition Parallelism实现的。Partition Elimination 是指在执行TSql查询的时候，不是seek表的所有分区，而是根据Partition column排除部分分区，在符合 filtering the partition column 条件的 partition 上进行查询。Partition Parallelism是指分区之间可以并发执行查询。分区表查询使用更小的查询范围，更高的并发度，因而具有更高的查询性能。

一，Partition Elimination

A key benefit of table partitioning is partition elimination, whereby the query processor can eliminate inapplicable partitions of a table or index from a query plan. The more fine-grained the query filter is on the partition column, the more partitions can be eliminated and the more efficient the query can become. Partition elimination can occur with table partitions, index-aligned partitions, and partition-aligned indexed views in both SQL Server 2008 and SQL Server 2005. Partition elimination can also occur with nonaligned indexes.

实现分区消除主要有两种方式

1，Filtering the partition column

SQL Server 2008 adds a new partition-aware seek operation as the mechanism for partition elimination. It is based on a hidden computed column created internally to represent the ID of a table or index partition for a specific row. In effect, a new computed column, a partition ID, is added to the beginning of the clustered index of the partitioned table.

Partition elimination is most useful when a large set of table partitions are eliminated, because partition elimination helps reduce the amount of work needed to satisfy the query. So the key point is to filter on as small a number of partitions as possible based on filtering the partition column.

2，Join Collocation

If you query two tables that are partitioned with compatible partition functions, you may be able to join the two tables on their partition column. In that case, SQL Server may be able to pair up the partitions from each table and join them at the partition level. This is called ‘join collocation‘, implying compatibility between the partitions of the two tables that is leveraged in the query.

二，Partitioned Table Parallelism
Parallel operations are a key benefit of table partitioning. Indexes can be rebuilt in parallel, and the query processor can take advantage of multiple partitions to access a table in parallel.
If a partitioned table is sufficiently large and at least two CPU cores are available to SQL Server, a parallel execution strategy is used across the partitions that the query filter resolves to. Generally speaking, SQL Server attempts to balance the number of threads assigned to various partitions. The max degree of parallelism setting (which you set by using the sp_configure stored procedure or the MAXDOP query hint) determines the available thread count.
However, if the filter of the query specifically calls out ranges that determine a subset of the partitions so that partition elimination can occur, the number of partitions accessed will accordingly be less.

SQL Server 2005 was optimized for queries filtered to one partition. For such queries, more than one available thread could be assigned to scan the partition in parallel. However, for a filtered query touching more than one partition, only one thread could be assigned to any given partition. In SQL Server 2008, if the number of available threads is greater than the partitions accessed by a filtered query, more than one thread can be assigned to access data in each partition. This can improve performance in filtered queries that access more than one partition. 

三，Designing Partitions to Improve Query Performance

参考文档：

https://msdn.microsoft.com/en-us/library/dd578580.aspx

https://msdn.microsoft.com/en-us/library/ms177411(v=sql.105).aspx

Partition Table 查询性能

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原文地址：http://www.cnblogs.com/ljhdo/p/5040252.html