replacement_sort_tuples
When the number of tuples to be sorted is smaller than this number, a sort will produce its first output run using replacement selection rather than quicksort. This may be useful in memory-constrained environments where tuples that are input into larger sort operations have a strong physical-to-logical correlation. Note that this does not include input tuples with an inverse correlation. It is possible for the replacement selection algorithm to generate one long run that requires no merging, where use of the default strategy would result in many runs that must be merged to produce a final sorted output. This may allow sort operations to complete sooner. The default is 150,000 tuples. Note that higher values are typically not much more effective, and may be counter-productive, since the priority queue is sensitive to the size of available CPU cache, whereas the default strategy sorts runs using a cache oblivious algorithm. This property allows the default sort strategy to automatically and transparently make effective use of available CPU cache. Setting maintenance_work_mem to its default value usually prevents utility command external sorts (e.g., sorts used by CREATE INDEX to build B-Tree indexes) from ever using replacement selection sort, unless the input tuples are quite wide.
英文手册覆盖始于 PostgreSQL 7.4. 来源历史与运行验证各自保留独立版本边界。
当前阅读 PG 10·选择有来源记录的版本
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- boot val
- 150000
- category
- Resource Usage / Memory
- context
- user
- documented
- true
- enumvals
- 未知
- extra desc
- When more tuples than this are present, quicksort will be used.
- lang
- en
- max val
- 2147483647
- metadata version
- 10
- min val
- 0
- name
- replacement_sort_tuples
- short desc
- Sets the maximum number of tuples to be sorted using replacement selection.
- source
- pg-settings-source-snapshot
- unit
- 未知
- vartype
- integer
版本定义 PG 10
When the number of tuples to be sorted is smaller than this number, a sort will produce its first output run using replacement selection rather than quicksort. This may be useful in memory-constrained environments where tuples that are input into larger sort operations have a strong physical-to-logical correlation. Note that this does not include input tuples with an inverse correlation. It is possible for the replacement selection algorithm to generate one long run that requires no merging, where use of the default strategy would result in many runs that must be merged to produce a final sorted output. This may allow sort operations to complete sooner. The default is 150,000 tuples. Note that higher values are typically not much more effective, and may be counter-productive, since the priority queue is sensitive to the size of available CPU cache, whereas the default strategy sorts runs using a cache oblivious algorithm. This property allows the default sort strategy to automatically and transparently make effective use of available CPU cache. Setting maintenance_work_mem to its default value usually prevents utility command external sorts (e.g., sorts used by CREATE INDEX to build B-Tree indexes) from ever using replacement selection sort, unless the input tuples are quite wide.
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定义来源
center · PostgreSQL 10 · english-manuals:7031858dd481798b16e0cb60e7a76b848d13309cbf6b6da0e70fba7748a239bd
正文语言: en · english-manuals:7031858dd481798b16e0cb60e7a76b848d13309cbf6b6da0e70fba7748a239bd