然后第二个话题是关于参数optimizer_dynamic_sampling。o小白研究这个参数的起因是由于自己在做关于CBO的实验的时候发现oracle总是很智能,无论如何调整表的数据,oracle总是按照比较优的方式去走执行计划,而o小白从来没有收集过统计信息,在经过询问查询之后知道有这么一个参数。并且我们可以看到,在oracle10g的时候,有人推...
At the time of writing, there are some cases where index sampling can lead to NDV mis-estimates for composite indexes. The best work-around is to create a column group on the relevant columns and use gather_table_stats. Alternatively, there is a one-off fix - 27268249. This patch change...
At the time of writing, there are some cases where index sampling can lead to NDV mis-estimates for composite indexes. The best work-around is to create a column group on the relevant columns and use gather_table_stats. Alternatively, there is a one-off fix - 27268249. This patch change...
At the time of writing, there are some cases where index sampling can lead to NDV mis-estimates for composite indexes. The best work-around is to create a column group on the relevant columns and use gather_table_stats. Alternatively, there is a one-off fix - 27268249. This patch change...
Step 1. Oracle starts with a small sampling percentage. If histograms need to be gathered, Oracle might materialize the sample, depending on the sampling percentage. Step 2. Oracle gathers basic column statistics on the sample. For example, suppose a tableThas only one columnC1, then the basic...
enable_auto_refresh_location_cache用于设置是否开启自动刷新位置缓存信息逻辑。 属性描述 参数类型布尔类型 默认值True 取值范围 True False 是否重启 OBServer 生效否 配置示例 开启自动刷新位置缓存信息逻辑。 obclient>ALTER SYSTEM SET enable_auto_refresh_location_cache=True;...
sampling (1) sampling interval (1) sankey diagram (7) saperator (1) sattistics collector (1) save (16) save context (1) save defaults (1) save dimension (1) save error (8) save imagen (1) save message (1) save result (1) save state (1) save time (2) save view (1) saved...
sampling (1) sampling interval (1) sankey diagram (7) saperator (1) sattistics collector (1) save (16) save context (1) save defaults (1) save dimension (1) save error (8) save imagen (1) save message (1) save result (1) save state (1) save time (2) save view (1) saved...
trace_log_sampling_interval trace_log_slow_query_watermark trx_2pc_retry_interval tenant_groups use_large_pages user_block_cache_priority trx_force_kill_threshold user_row_cache_priority trx_try_wait_lock_timeout unit_balance_resource_weight virtual_table_location_cache_expire_time weak_read_version...
sampling of data will be an appropriate technique, because sampling can be performed much faster than computing the actual result. Therefore, during a given iteration of the recursive query execution, a value, such as a single table estimate, may be verified by issuing a dynamic compute query ...