Question

如果我查询1,2,3,4或5天的数据，我有一个使用日期索引的查询。对于这些查询，数据会在不到10秒的时间内恢复。 6天或更长时间，它决定不使用索引和查询需要永远，如果它回来了。如果我尝试使用索引帮助它似乎没有使用索引。我尝试对索引和表格进行收集统计。这是查询（在这种情况下，9天的数据）：

select 

                        r.range_text as duration_range,
                        nvl(count(c.call_duration),0) as calls,
                        nvl(SUM(call_duration),0) as total_duration
                    from
                        duration_ranges r
                    left join
                        big_table c
                    on c.call_duration >= r.range_lbound AND c.call_duration <= r.range_ubound

                    where calltimestamp_local >= to_date('20-02-2014 00:00:00','dd-MM-yyyy HH24:mi:ss')
                    and calltimestamp_local <= to_date('28-02-2014 23:59:59' ,'dd-MM-yyyy HH24:mi:ss')
                     and  c.destinationnumber = 'sip:1000@company.com:5060;user=phone'
                    group by
                    r.range_text
                order by
                    r.range_text;

这是没有索引的解释计划：

Without Index
SELECT STATEMENT  ALL_ROWSCost: 827,605  Bytes: 1,344  Cardinality: 14                          
    8 SORT GROUP BY  Cost: 827,605  Bytes: 1,344  Cardinality: 14                   
        7 MERGE JOIN  Cost: 827,486  Bytes: 246,552,768  Cardinality: 2,568,258                 
            2 SORT JOIN  Cost: 4  Bytes: 308  Cardinality: 14           
                1 TABLE ACCESS FULL TABLE MYDB.DURATION_RANGES Cost: 3  Bytes: 308  Cardinality: 14         
            6 FILTER            
                5 SORT JOIN  Cost: 827,471  Bytes: 14,164,118  Cardinality: 191,407         
                    4 PARTITION RANGE ALL  Cost: 824,134  Bytes: 14,164,118  Cardinality: 191,407  Partition #: 7  Partitions accessed #1 - #1653   
                        3 TABLE ACCESS FULL TABLE MYDB.BIG_TABLE Cost: 824,134  Bytes: 14,164,118  Cardinality: 191,407  Partition #: 7  Partitions accessed #1 - #1653

使用索引：

With Index
Plan
SELECT STATEMENT  ALL_ROWSCost: 822,732  Bytes: 1,344  Cardinality: 14                          
    8 SORT GROUP BY  Cost: 822,732  Bytes: 1,344  Cardinality: 14                   
        7 MERGE JOIN  Cost: 822,635  Bytes: 205,460,736  Cardinality: 2,140,216                 
            2 SORT JOIN  Cost: 4  Bytes: 308  Cardinality: 14           
                1 TABLE ACCESS FULL TABLE MYDB.DURATION_RANGES Cost: 3  Bytes: 308  Cardinality: 14         
            6 FILTER            
                5 SORT JOIN  Cost: 822,621  Bytes: 11,803,444  Cardinality: 159,506         
                    4 TABLE ACCESS BY GLOBAL INDEX ROWID TABLE MYDB.BIG_TABLE Cost: 819,841  Bytes: 11,803,444  Cardinality: 159,506  Partition #: 7  Partition access computed by row location 
                        3 INDEX RANGE SCAN INDEX MYDB.IDX_CDR_CALLTIMESTAMP_LOCAL Cost: 2,744  Cardinality: 850,691

任何想法为什么它不能使用索引如果在5天的数据中它会快速恢复？它似乎并没有优化，因为它回来的速度要慢得多。

Answer 1

也许它的工作速度较慢，因为数据和索引不会有太大变化？您可以通过强制Oracle使用索引来轻松检查它 - 指定INDEX提示，然后将时间与索引进行比较，而不使用它来进行相同的查询。

您还可以指定NOINDEX提示，以比较5天或更短天数的时间。

为什么查询在Oracle中不使用索引

1 个答案: