Index full scan min max
Partition Table using min/max functions and Top N - Index selection and The candidate index is either not being used or is being used to scan or the correct index, it's just scanning the entire index instead of accessing 21 Oct 2013 A scan of the primary key and a table scan is therefore exactly the A wide range of additional optimizations became possible due to this. GROUP BY optimization (loose index scan, MIN/MAX optimization); Index merge. 21 сен 2012 4 | INDEX FULL SCAN ( MIN / MAX ) | IX_TEST_A | 1 | 3 | 2 (0)| 00:00:01 |. | 5 | SORT AGGREGATE | | 1 | 3 | | |. | 6 | FIRST ROW | | 1 | 3 | 2 (0)| Index lookup Data is accessed by looking up key values in an index and returning rowids. A rowid uniquely identifies an individual row in a particular data block. The goal is to take not max value using min/max scan, but rowid already with first index visit. MAX(rowid) KEEP(DENSE_RANK LAST ORDER BY a) looks like correct way to achieve this, but Oracle is not doing this. It chooses index full/range scan or even table full scan but not index min/max scan. INDEX FULL SCAN (MIN/MAX): Oracle is reading the entire index with multiblock reads. This is used when a query is select both the min and max values from a table and the index is relatively small. INDEX FULL SCAN (MIN/MAX) with two identical MIN() I’ve just noticed an interesting thing: Assume, that we have a simple query with “MIN(ID)” that works through “Index full scan(MIN/MAX)”: SQL> explain plan for 2 select 3 min(ID) as x 4 from tab1 5 where ID is not null; Explained.
Because it's INDEX FULL SCAN (MIN/MAX) I would have supposed it to be a O(log(n)) operation, both for MAX(id) and ORDER BY. Without an index, a Full Table Scan would be done with O(n) - but that's not the case here. Maybe recalculating the table statistics might help:
INDEX FULL SCAN (MIN/MAX) with two identical MIN() I’ve just noticed an interesting thing: Assume, that we have a simple query with “MIN(ID)” that works through “Index full scan(MIN/MAX)”: SQL> explain plan for 2 select 3 min(ID) as x 4 from tab1 5 where ID is not null; Explained. However, the Index Full Scan (Min/Max) can only visit one side of the index, not both. Therefore, if you want both the minimum and the maximum column value, an Index Full Scan (Min/Max) is not viable and the CBO is forced to look for other alternatives. It sounds like such a trivial thing to implement but that’s how it goes. The INDEX FULL SCAN (MIN/MAX) operation will do either an index scan for the first leaf block or an index scan for the last leaf block. It can not do both at the same time. Think about it The code to handle the operation would have to have some fairly specific logic in it to handle the dual calls. Locating most current record using ROW_NUMBER() vs. Index Full Scan (Min/Max) Very often when reading data, we need to locate the most current record for a set of conditions. One typical example is that we read the data to find the most recent order for a particular customer. Re: Is it possible to use Index Full Scan (Min/Max) on local index? 796772 Dec 27, 2010 12:19 PM ( in response to 695836 ) See, 1. you did not understand the question 2. you ask my plan (question not about my plan) 3. you give useless advice When somebody indicates you about it, you begin to calculate messages (this alone speaks volumes about you). Because it's INDEX FULL SCAN (MIN/MAX) I would have supposed it to be a O(log(n)) operation, both for MAX(id) and ORDER BY. Without an index, a Full Table Scan would be done with O(n) - but that's not the case here. Maybe recalculating the table statistics might help:
I'm having a bit of confusion about the INDEX FULL SCAN (MIN/MAX) operation. I expect this to be a super walk down either to min/max of the
The INDEX FULL SCAN (MIN/MAX) operation will do either an index scan for the first leaf block or an index scan for the last leaf block. It can not do both at the same time. Think about it The code to handle the operation would have to have some fairly specific logic in it to handle the dual calls. Locating most current record using ROW_NUMBER() vs. Index Full Scan (Min/Max) Very often when reading data, we need to locate the most current record for a set of conditions. One typical example is that we read the data to find the most recent order for a particular customer. Re: Is it possible to use Index Full Scan (Min/Max) on local index? 796772 Dec 27, 2010 12:19 PM ( in response to 695836 ) See, 1. you did not understand the question 2. you ask my plan (question not about my plan) 3. you give useless advice When somebody indicates you about it, you begin to calculate messages (this alone speaks volumes about you). Because it's INDEX FULL SCAN (MIN/MAX) I would have supposed it to be a O(log(n)) operation, both for MAX(id) and ORDER BY. Without an index, a Full Table Scan would be done with O(n) - but that's not the case here. Maybe recalculating the table statistics might help: The Index Full Scan can only visit one side of the index. When you are doing . SELECT MIN(SDATE), MAX(SDATE) FROM MYTABLE you are requesting to visit 2 sides. Therefore, if you want both the minimum and the maximum column value, an Index Full Scan is not viable. A more detailed analyze you can find here. •At least one of the index columns is not null. A full scan can be used to eliminate a sort operation, because the data is ordered by the index key. It reads the blocks singly. Fast full index scans are an alternative to a full table scan when the index contains all the columns that are needed for the query,
Locating most current record using ROW_NUMBER() vs. Index Full Scan (Min/Max) Very often when reading data, we need to locate the most current record for a set of conditions. One typical example is that we read the data to find the most recent order for a particular customer.
INDEX (FULL SCAN (MIN/MAX)) Description. Returns the first or last entry in the index. Versions. This operation was introduced in Oracle 8.1.5 This operation is implemented in the following versions Wrong Results Involving INDEX FULL SCAN (MIN/MAX) in 12.1.0.2. One of my customers that recently upgraded to 12c hit a bug (22913528) that I think is good to be aware of. Note that as the title of this post states, the problem only occur in 12.1.0.2. If you check out his post, you'll see the details of his tests. Basically, he was wondering why the optimizer would choose to do a full table scan instead of using an INDEX FULL SCAN (MIN/MAX) operation for a query that contained both a MIN and a MAX function call on the same indexed column. INDEX RANGE SCAN (MIN/MAX) INDEX_NEW(cr=4 pr=3 pw=0 time=13194 us)(object id 38922) 3. Through the ASH report, we could see there were many versions like this SQL in the “TOP SQL using literals”. So we suggested to use bind variables instead of specific values to reduce hard parse. So perhaps the optimizer will use the index min/max range scan with a cost that is roughly 2 branch blocks plus total leaf blocks / 20 (since there are 20 distinct values for line_nr ); maybe it would divide the leaf block estimate by two because “on average” – i.e. for repeated random selections of value for id – it would have to scan half
However, the Index Full Scan (Min/Max) can only visit one side of the index, not both. Therefore, if you want both the minimum and the maximum column value, an Index Full Scan (Min/Max) is not viable and the CBO is forced to look for other alternatives. It sounds like such a trivial thing to implement but that’s how it goes.
Partition Table using min/max functions and Top N - Index selection and The candidate index is either not being used or is being used to scan or the correct index, it's just scanning the entire index instead of accessing
INDEX FULL SCAN (MIN/MAX): Oracle is reading the entire index with multiblock reads. This is used when a query is select both the min and max values from a table and the index is relatively small. INDEX FULL SCAN (MIN/MAX) with two identical MIN() I’ve just noticed an interesting thing: Assume, that we have a simple query with “MIN(ID)” that works through “Index full scan(MIN/MAX)”: SQL> explain plan for 2 select 3 min(ID) as x 4 from tab1 5 where ID is not null; Explained. However, the Index Full Scan (Min/Max) can only visit one side of the index, not both. Therefore, if you want both the minimum and the maximum column value, an Index Full Scan (Min/Max) is not viable and the CBO is forced to look for other alternatives. It sounds like such a trivial thing to implement but that’s how it goes. The INDEX FULL SCAN (MIN/MAX) operation will do either an index scan for the first leaf block or an index scan for the last leaf block. It can not do both at the same time. Think about it The code to handle the operation would have to have some fairly specific logic in it to handle the dual calls.