I want to delete around 1 million records from a table which is partitioned and table size is around 10-13 millions , As of now only 2 partition exist in the table containining July month data and august month data, and i want to delete from July month.Can you please let me know if a simple delete from table paritition (0715) is ok to do ? Possibilities of fragmentation ? or any best way out?
Thank you
DELETE is rather costly operation on large partitioned tables (but 10M is not realy large). Typically you try to avoid it and remove the data partition-wise using drop partition.
The simplest schema is rolling window, where you define a range partitioning schema by dropping the oldest partitian after the retention interval.
If you need more controll you may use CTAS and exchange back approach.
Instead of deleting a large part of a partition create a copy of it
create table TMP as
select * from TAB PARTITION (ppp)
where <predicate to filter out records to be ommited for partition ppp>
Create indexes on the TMP table in the same structure as the LOCAL indexes of the partitioned table.
Than exchange the temporary table with the partition
ALTER TABLE TAB
EXCHANGE PARTITION ppp WITH TABLE TMP including indexes
WITHOUT VALIDATION
Note no fragmenatation as a result, in contrary you may use it to reorganize the partition data (e.g. with ORDER BY in CTAS or with COMPRESS etc.)
You can delete truncate the partition from the given table. Delete also you can perform if you want to delete few rows from the partition. Plz share your table structure along with the partition details so that it will be easy for people here to assist you.
Related
We have a primary table that is Range partitioned by date with a 1-month interval. It's also a list sub-partitioned with 4 distinct values. So essentially it is one month partition having 4 sub-partitions.
Database: Oracle 19c
I need advice on how to effectively move the partition/sub-partition data from active schema to historical schema in another database.
Also, there are about 30 tables that are referenced partitioned on the primary table for which the data needs to be moved as well. Overall I'm looking to move about 2500 subpartitions
I'm not sure if an exchange partition would be the right approach in this scenario?
TIA
You could use exchange to get the data rapidly out of your active table, but you would still then to send that table over the wire to the remote history database to load it in.
In which case, using "exchange" probably is just adding more steps to the process for little gain. (There are still potential uses here depending on how you want to handle indexing etc).
But simplest is perhaps just transferring the data over, assuming a common structure between the two tables, ie
insert /*+ APPEND */ into history_table#remote_db
select * from active_table partition ( myparname )
I can't remember if partition naming syntax is supported over a db link, but if not, then the appropriate date predicates will do the same trick, and then just follow up with:
alter table active_table truncate partition myparname;
I wanna know how hive partitioning works I know the concept but I am trying to understand how its working and store the in exact partition.
Let say I have a table and I have created partition on year its dynamic, ingested data from 2013 so how hive create partition and store the exact data in exact partition.
If the table is not partitioned, all the data is stored in one directory without order. If the table is partitioned(eg. by year) data are stored separately in different directories. Each directory is corresponding to one year.
For a non-partitioned table, when you want to fetch the data of year=2010, hive have to scan the whole table to find out the 2010-records. If the table is partitioned, hive just go to the year=2010 directory. More faster and IO efficient
Hive organizes tables into partitions. It is a way of dividing a table into related parts based on the values of partitioned columns such as date.
Partitions - apart from being storage units - also allow the user to efficiently identify the rows that satisfy a certain criteria.
Using partition, it is easy to query a portion of the data.
Tables or partitions are sub-divided into buckets, to provide extra structure to the data that may be used for more efficient querying. Bucketing works based on the value of hash function of some column of a table.
Suppose you need to retrieve the details of all employees who joined in 2012. A query searches the whole table for the required information. However, if you partition the employee data with the year and store it in a separate file, it reduces the query processing time.
I'm working with an application that has a large amount of outdated data clogging up a table in my databank. Ideally, I'd want to delete all entries in the table whose reference date is too old:
delete outdatedTable where referenceDate < :deletionCutoffDate
If this statement were to be run, it would take ages to complete, so I'd rather break it up into chunks with the following:
delete outdatedTable where referenceData < :deletionCutoffDate and rownum <= 10000
In testing, this works suprisingly slowly. The following query, however, runs dramatically faster:
delete outdatedTable where rownum <= 10000
I've been reading through multiple blogs and similar questions on StackOverflow, but I haven't yet found a straightforward description of how/whether using rownum affects the Oracle optimizer when there are other Where clauses in the query. In my case, it seems to me as if Oracle checks
referenceData < :deletionCutoffDate
on every single row, executes a massive Select on all matching rows, and only then filters out the top 10000 rows to return. Is this in fact the case? If so, is there any clever way to make Oracle stop checking the Where clause as soon as it's found enough matching rows?
How about a different approach without so much DML on the table. As a permanent solution for future you could go for table partitioning.
Create a new table with required partition(s).
Move ONLY the required rows from your existing table to the new partitioned table.
Once the new table is populated, add the required constraints and indexes.
Drop the old table.
In future, you would just need to DROP the old partitions.
CTAS(create table as select) is another way, however, if you want to have a new table with partition, you would have to go for exchange partition concept.
First of all, you should read about SQL statement's execution plan and learn how to explain in. It will help you to find answers on such questions.
Generally, one single delete is more effective than several chunked. It's main disadvantage is extremal using of undo tablespace.
If you wish to delete most rows of table, much faster way usially a trick:
create table new_table as select * from old_table where date >= :date_limit;
drop table old_table;
rename table new_table to old_table;
... recreate indexes and other stuff ...
If you wish to do it more than once, partitioning is a much better way. If table partitioned by date, you can select actual date quickly and you can drop partion with outdated data in milliseconds.
At last, paritioning if a way to dismiss 'deleting outdated records' at all. Sometimes we need old data, and it's sad if we delete it by own hands. With paritioning you can archive outdated partitions outside of the database, but connects them when you need to access old data.
This is an old request, but I'd like to show another approach (also using partitions).
Depending on what you consider old, you could create corresponding partitions (optimally exactly two; one current, one old; but you could just as well make more), e.g.:
PARTITION BY LIST ( mod(referenceDate,2) )
(
PARTITION year_odd VALUES (1),
PARTITION year_even VALUES (0)
);
This could as well be months (Jan, Feb, ... Dec), decades (XX0X, XX1X, ... XX9X), half years (first_half, second_half), etc. Anything circular.
Then whenever you want to get rid of old data, truncate:
ALTER TABLE mytable TRUNCATE PARTITION year_even;
delete from your_table
where PK not in
(select PK from your_table where rounum<=...) -- these records you want to leave
I have a table which has two partitions (by range): first_half and second_half based on a column "INSERT_DAY".
I need to add subpartitions "SUCCESS" and "NONSUCCESS" based on the values of another column "STATUS" (subpartition by list) i.e. I need to transform my range partition to composite (range-list) partition.
I do not wish to drop existing tables or partitions. What is the ALTER query for this?
PS: The database is Oracle 9i
No alter query for adding subpartitions as far as i know.
To get the desired result performe the folowing steps
Create the table in the structure you want using create as select with the partitions and the sub partitions.
switch the names of the two tables.
you can also explore the use of dbms_Redefinition but if you have a luxury of a littel downtime it's not worth it.
So, I have a .NET program doing batch loading of records into partitioned tables using array bound stored procedure calls via Oracle ODP.NET, but that's neither here nor there.
What I would like to know is: because I have a partitioned index on said tables, the speed of the batch load is pretty slow. I fully understand that I cannot drop an index partition, but I would obviously prefer not to have to drop and rebuild the entire index since that will take considerably more time to execute. Is this my only recourse?
Is there a fairly simple way to drop the partition itself and then rebuild the partition and index partition that would save time and go about accomplishing my goal?
Are you loading an entire partition at once? Or are you merely adding new rows to an existing partition? Are all the indexes equipartitioned with the table?
Normally, if you are loading data into a partitioned table, your partitioning scheme is chosen so that each load will put data into a fresh partition. If that is the case, you can use partition exchange to load the data. In a nutshell, you load data into an (unindexed) staging table whose structure matches the real table, you create the indexes to match the indexes on the real table, and then do
ALTER TABLE partitioned_table
EXCHANGE PARTITION new_partition_name
WITH TABLE staging_table_name
WITHOUT VALIDATION;