We have a table with 120 partitions on date range which in turn is subpartitioned again on range.
Each partition has around 200 million records, the conventional way of changing the datatype will make our production unresponsive for hours.Is there any better way for changing the datatype of such a huge table?
We have already tried the following options:
Exchange partition. This does not work.
Create a new table with the same structure as the existing one and the altered column, and inserting the data using /*+ append *. It again takes hours.
Currently the column size is varchar2(30). We need to change it to:
ALTER TABLE ORDERS MODIFY (INFO VARCHAR2(50) );
Changing varchar2(30) to varchar2(50) should work instantly and should not cause any trouble.
You modify just some meta data but actual table data is not touched.
I am trying to load the tables into oracle in-memory database. I have enable the tables for INMEMORY by using sql+ command ALTER TABLE table_name INMEMORY. The table also contains data i.e. the table is populated. But when I try to use the command SELECT v.owner, v.segment_name name, v.populate_status status from v$im_segments v;, it shows no rows selected.
What can be the problem?
Have you considered this?
https://docs.oracle.com/database/121/CNCPT/memory.htm#GUID-DF723C06-62FE-4E5A-8BE0-0703695A7886
Population of the IM Column Store in Response to Queries
Setting the INMEMORY attribute on an object means that this object is a candidate for population in the IM column store, not that the database immediately populates the object in memory.
By default (INMEMORY PRIORITY is set to NONE), the database delays population of a table in the IM column store until the database considers it useful. When the INMEMORY attribute is set for an object, the database may choose not to materialize all columns when the database determines that the memory is better used elsewhere. Also, the IM column store may populate a subset of columns from a table.
You probably need to run a select against the date first
When I execute the UPSERT command on apache phoenix, I always see that Phoenix add an extra column (named _0) with an empty value in the hbase, this column(_0) is auto generate by phoenix, but I don't need it, like this:
ROW COLUMN+CELL
abc column=F:A,timestamp=1451305685300,value=123
abc column=F:_0, timestamp=1451305685300, value= # I want to avoid generate this row
Could you tell me how to avoid that? Thank you very much!
"At create time, to improve query performance, an empty key value is
added to the first column family of any existing rows or the default
column family if no column families are explicitly defined. Upserts will also add this empty key value. This improves query performance by having a key value column we can guarantee always being there and thus minimizing the amount of data that must be projected and subsequently returned back to the client."
Apache Phoenix Documentation
Regarding your question if that is avoidable:
You could work around the problem by adding the following statements at the end of your sql:
ALTER TABLE "<your-table>" ADD "<your-cf>"."_0" VARCHAR(1);
ALTER TABLE "<your-table>" DROP COLUMN "<your-cf>"."_0";
You should only do this if you query some table with phoenix but then access the table with another system that is not aware of this phoenix-specific dummy value.
I have an existing table with millions of records. Now I want to add a new column with default value. But for performances reasons I don't want to apply the new value immediately to existing records. Is there one handy way to do it?
So far, what in my mind is to work around this issue is to:
Add the new column, but do not specify a default (DDL)
Update by chunk the old rows to the default value (to avoid locking the table) (DML)
COMMIT
Alter the column to add a default (DDL)
Another option would be
Add the new column without any default value but make it accept
NULL
While inserting new record, insert NULL for this column
CREATE a AFTER INSERT trigger and update the column with it's
default value.
Something like
CREATE TRIGGER trg_update
AFTER INSERT
ON table_name
BEGIN
UPDATE table_name
SET new_column = (default_value)
WHERE Id_Column = :new.Id_Column;
END;
I'm trying to create a new row in a table. There are two constraints on the table -- one is on the key field (DB_ID), the other constrains a value to be one of several the the field ENV. When I do an insert, I do not include the key field as one of the fields I'm trying to insert, yet I'm getting this error:
unique constraint (N390.PK_DB_ID) violated
Here's the SQL that causes the error:
insert into cmdb_db
(narrative_name, db_name, db_type, schema, node, env, server_id, state, path)
values
('Test Database', 'DB', 'TYPE', 'SCH', '', 'SB01', 381, 'TEST', '')
The only thing I've been able to turn up is the possibility that Oracle might be trying to assign an already in-use DB_ID if rows were inserted manually. The data in this database was somehow restored/moved from a production database, but I don't have the details as to how that was done.
Any thoughts?
Presumably, since you're not providing a value for the DB_ID column, that value is being populated by a row-level before insert trigger defined on the table. That trigger, presumably, is selecting the value from a sequence.
Since the data was moved (presumably recently) from the production database, my wager would be that when the data was copied, the sequence was not modified as well. I would guess that the sequence is generating values that are much lower than the largest DB_ID that is currently in the table leading to the error.
You could confirm this suspicion by looking at the trigger to determine which sequence is being used and doing a
SELECT <<sequence name>>.nextval
FROM dual
and comparing that to
SELECT MAX(db_id)
FROM cmdb_db
If, as I suspect, the sequence is generating values that already exist in the database, you could increment the sequence until it was generating unused values or you could alter it to set the INCREMENT to something very large, get the nextval once, and set the INCREMENT back to 1.
Your error looks like you are duplicating an already existing Primary Key in your DB. You should modify your sql code to implement its own primary key by using something like the IDENTITY keyword.
CREATE TABLE [DB] (
[DBId] bigint NOT NULL IDENTITY,
...
CONSTRAINT [DB_PK] PRIMARY KEY ([DB] ASC),
);
It looks like you are not providing a value for the primary key field DB_ID. If that is a primary key, you must provide a unique value for that column. The only way not to provide it would be to create a database trigger that, on insert, would provide a value, most likely derived from a sequence.
If this is a restoration from another database and there is a sequence on this new instance, it might be trying to reuse a value. If the old data had unique keys from 1 - 1000 and your current sequence is at 500, it would be generating values that already exist. If a sequence does exist for this table and it is trying to use it, you would need to reconcile the values in your table with the current value of the sequence.
You can use SEQUENCE_NAME.CURRVAL to see the current value of the sequence (if it exists of course)