用Delete与Truncate清除表数据对高水位的影响-Mysql Tutorial-php.cn

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用Delete与Truncate清除表数据对高水位的影响

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Jun 07, 2016 pm 04:44 PM

truncate

众所周知，Oracle段都有一个在段内容纳数据块的上限，我们把这个上限称为High Water Mark（HWM）。这个HWM是一个标记，用来说明

从block_id字段的值可以发现，当在表中插入数据后，分配给表的block从128开始一直到1152，并且，开始的1-16个extent会以8个块（8*8=64K）为分配单位，而到了第17个extent之后，，则以128个块（8*128=1M）为分配单位，目前ZLM1表共分配了24个extent

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