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Oracleで大量データのinsertとdeleteを繰り返すと遅くなる理由
WebAug 31, 2024 · Oracle高水位线HWM降低技巧. 1.什么是高水位线? 高水位线(high-water mark,HWM) 在数据库中,如果把表想象成从左到右依次排开的一系列块,高水位线就是曾经包含了数据 的最右边的块。 原则上 HWM 只会增大, 即使将表中的数据全部删除,HWM 也 … WebNov 1, 2010 · The High Water Mark is the maximum number of blocks which have ever contained data. Deleting records from a table frees up the space but does not move the HWM. In order to reset the High Water Mark we have to drop and recreate the table, or just truncate it. Normally we wouldn't bother. However, the High Water Mark defines the range … cancel fingerhut account
表の断片化が進んでいる、索引が肥大化している判断の基準
WebMay 28, 2024 · Suppose you load the table with 1 million rows .Now you will have suppose the high water mark as 1 GB. Now if you delete all the 1 millions rows, then even the high water mark will be remain same as 1 GB. The only way to reduce the HWM is to rebuild the able or use truncate table. Oracle Truncate table reduce the High water mark WebThe remedy for a too-high high water mark (e.g. a fragmented table will lots of empty blocks) is to reorganize the table with Data Pump (expdp and impdp), the dbms_redefinition utility, or with the table shrink or coalesce Also see my notes on method for lowering a table high water mark. Also see my notes on sessions high water mark. WebOct 23, 2024 · 数据库中表不断的insert,delete,update,导致表和索引出现碎片。这会导致HWM之前有很多的空闲空间,而oracle在做全表扫描的时候会读取HWM一下的所有块,这样会产生更多的IO,影响性能。oracle提供了shrink space碎片整理的功能,对于索引要采取rebuild online的方式进行碎片整理。 fishing rod bank holder