定制统计信息收集策略

下面脚本用于收集SCOTT账户下统计信息过期了或者是从没收集过统计信息的表的统计信息，采样率也根据表的段大小做出了相应调整。

declare
  cursor stale_table is
    select owner,
           segment_name,
           case
             when segment_size < 1 then
              100
             when segment_size >= 1 and segment_size <= 5 then
              50
             when segment_size > 5 then
              30
           end as percent,
           6 as degree
      from (select owner,
                   segment_name,
                   sum(bytes / 1024 / 1024 / 1024) segment_size
              from DBA_SEGMENTS
             where owner = 'SCOTT'
               and segment_name in
                   (select table_name
                      from DBA_TAB_STATISTICS
                     where (last_analyzed is null or stale_stats = 'YES')
                       and owner = 'SCOTT')
             group by owner, segment_name);
begin
  dbms_stats.flush_database_monitoring_info;
  for stale in stale_table loop
    dbms_stats.gather_table_stats(ownname          => stale.owner,
                                  tabname          => stale.segment_name,
                                  estimate_percent => stale.percent,
                                  method_opt       => 'for all columns size repeat',
                                  degree           => stale.degree,
                                  cascade          => true);
  end loop;
end;
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