I see that one of my queries from an application time is spending most of its time in the hash group by. I'm running Oracle 11g with a quarter rack exadata appliance. Is there a better way to run or design this table? query:
One of our client is using Oracle DB 10.2 with customize applications. They have 5 schemas (one for each module). In their Head Office they are utilizing 4 schemas and remaining one is being utilized on company site based in another city. Due to internet connectivity issue they don't have VPN available so they export schema dump file (imp/exp) on daily basis from that server, transfer it using FTP then import it on Production Server (in Head Office) on daily basis.
Now they are looking for an alternate because the schema size is getting larger day by day and due to internet connectivity issue they face lots of problems while transferring the file.
I'm trying to group sets of data based on time separations between records and then count how many records are in each group.
In the example below, I want to return the count for each group of data, so Group 1=5, Group 2=5 and Group 3=5
SELECT AREA_ID AS "AREA ID", LOC_ID AS "LOCATION ID", TEST_DATE AS "DATE", TEST_TIME AS "TIME" FROM MON_TEST_MASTER WHERE AREA_ID =89 AND LOC_ID ='3015' AND TEST_DATE ='10/19/1994';
[code]....
Group 1 = 8:00:22 to 8:41:22
Group 2 = 11:35:47 to 11:35:47
Group 3 = 15:13:46 to 15:13:46
Keep in mind the times will always change, and sometime go over the one hour mark, but no group will have more then a one hour separation between records.
I read that rownum is applied after the selection is made and before "order by". So, in order to get the sum of salaries for all employees in all departments with a row number starting from 1, i wrote :
select ROWNUM,department_id,sum(salary) from employees group by department_id
If i remove rownum, it gives the correct output. Why can't rownum be used here ?
If i have a table T1 and a table T2. Table T1 is having 100 rows and table T2 is having 20 rows. When performing a Hash join ,which table should be used to make the hash table ,the larger one or the smaller one and why ?IF the data set is too small for considerations then please conser table T1 with 10 million of rows and table T2 with 1 million of rows.
I see one of my SQL's which is ran by the user on a 10.2.0.3 database changing its SQL_ID after some runs even if the query is not changed a bit! However the HASH VALUE for this query remains the same.
how a same query can have different SQL_ID's but same HASH_VALUE?
Note: Statistics are not modified on the base tables of this query.
I am facing a problem in fetching / updating records from a customer details table having around 20 million records. The table contains around 30 fields with 'MOBILE_NO' as primary key. most of the queries are having 'mobile_no' in where clause .I am planning to hash partition that table using mobile_no column as there is no other column available which can be used for partition.
clarify whether creating hash partition on such key would increase performance of data extraction as I have read on net that hash partitioning is not effective for performance tuning.
A basic select and group by query I am optimising for my Database course has returned results that indicate it will perform better on a clustered index when returning a smaller number of rows (5% of the largest table) and on a hash clustered index when returning higher volumes (50% and 80%). I understand that it is possible to use more than one index type on a table to improve performance, but I am struggling to understand how I might establish a hash cluster and a cluster on the same table? and then use hints to drive the query down one access path or the other.
create tablespace mssm datafile 'c:appmssm01.dbf' size 100m segment space management manual;
create cluster hash_cluster_4k ( id number(2) ) size 8192 single table hash is id hashkeys 4 tablespace mssm;
-- Created a table in cluster with row size such that only one record fits one block and inserted 5 records each with a distinct key value
CREATE TABLE hash_cluster_tab_8k ( id number(2) , txt1 char(2000), txt2 char(2000), txt3 char(2000) ) CLUSTER hash_cluster_8k( id ); [code]....
If I issue the same query after creating unique index on hash_cluster_tab(id), the execution plan shows hash access and single I/O (cr = 1).Does it mean that to have single I/o in a single table hash cluster, we have to create unique index? Won't it create additional overhead of maintaining an index?
What is the second I/O needed for in case unique index is absent?
I have a existing non partition table with more than 100 million records,planning to re design using Hash partition.This table doesn't has any range column to do range partitioning.
Table has 40 columns with a Primary Key on two columns (guest_sales_Id ,Version Flag). guest_sales_Id is unique for entire table but with anopther column version Flag declared as Primary key.(Version Falg will have only two distinct values in entire table)
If i do hash partition,do i need to declare on two columns which are declared ad Primary key ?If i use only guest_sales_id to declare hash prtition any issues ?
I created the 32 hash partition on a fact table. Based on hash parititon technique it should evenly distribute data accross the different partition.But when i analyze the table and check the distribution its not at all even.
I was reading the documentation for oracle 11gr2, with reference to URL>.....
The following examples show how to correctly choose the cluster key and set the HASH IS, SIZE, and HASHKEYS parameters. For all examples, assume that the data block size is 2K and that on average, 1950 bytes of each block is available data space (block size minus overhead).Note that 34 hash keys are assigned for each data block
how they arrive at 34 hash keys because another portion of the document states
This space determines the maximum number of cluster or hash values stored in a data block. If SIZE is not a divisor of the data block size, then Oracle Database uses the next largest divisor.
if that is the case, then number of hash keys should be 1900/55 = 34.55 which should have rounded up to 35.
At moment we use range-hash partitioning of a large dimension table (dimension model warehouse) table with 2 levels - range partitioned on columns only available at bottom level of hierarchy - date and issue_id.
Result is a partition with null value - assume would get a null partition in large fact table if was partitioned with reference to the large dimension.Large fact table similarly partitioned date range-hash local bitmap indexes
Suggested to use would get automatic partition-wise joins if used reference partitioningWould have thought would get that with range-hash on both dimension.
While trying partition exchange feature of Oracle with 2 hash partitioned tables, I come to know that I can't directly exchange partitions between 2 partitioned tables
I have two hash partitioned tables , so to move partition data from one table to another will include-
1) Exchange from partitioned table to non-partitioned table. 2) exchange from non-partitioned table to new partitioned table.
But I am not sure in which hash partition my data will go in new partitioned table (data need to be moved has single key value on basis of which tables are partitioned),
I want to know how the Oracle optimizer choose joins and apply them while executing the query. So that I will insure about optimizer join before writing any query.
Can I add range sub partition to a hash partition table. Example like this.
CREATE TABLE test ( test_id VARCHAR2(10 ) , test_TYPE VARCHAR2(5) , CREATE_DATE date ) partition by hash (test_id, test_type) Partitions 3 SUBPARTITION BY RANGE (CREATE_DATE);
When Tried, I am getting syntax error as invalid option.
I'm using this code, and it performs fine, but I'm wondering if there is a more elegant way to do it--maybe with "ROLLBACK". Basically (as you can see) I need to get a normal count for each group but also for each group take a percentage of the total count (so all groups pct adds up to 100 (oh yeah, don't test for zero below, but just a test... )
select c.Event, c.code, count(1) as calls, total.total_count, count(1) / total.total_count * 100 as pct_of_total from table1 c
[Code]....
[Edit MC: add code tags, do it yourself next time]
