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类型: integer
默认: 4096
最低限度: 64
最大: 2147483647
单元: KB
上下文: user
重新开始: false

指定在写到临时磁盘文件之前被内部排序操作和哈希表使用的内存量。该值默认为四兆字节(4MB)。注意对于一个复杂查询, 可能会并行运行好几个排序或者哈希操作;每个操作都会被允许使用这个参数指定的内存量,然后才会开始写数据到临时文件。同样,几个正在运行的会话可能并发进行这样的操作。因此被使用的总内存可能是work_mem值的好几倍,在选择这个值时一定要记住这一点。ORDER BYDISTINCT和归并连接都要用到排序操作。哈希连接、基于哈希的聚集以及基于哈希的IN子查询处理中都要用到哈希表。

建议 [EN]

Sets the limit for the amount of non-shared RAM available for each query operation, including sorts and hashes. This limit acts as a primitive resource control, preventing the server from going into swap due to overallocation. Note that this is non-shared RAM per operation, which means large complex queries can use multple times this amount. Also, work_mem is allocated by powers of two, so round to the nearest binary step. The second formula is for reporting and DW servers which run a lot of complex queries.

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