Is it possible from spring to listen to table insert or update even if the table is inserted/updated outside the spring application process?
One suggestion: you need to do some extra works base on your RDBMS
- Create triggers for each of your listening tables, this trigger
should base on a new change on these table to update information to
somewhere else
- Create a table (named: datalogger)to store the data come from the trigger above, for example, when table1 has new record inserted, the
trigger (named: trigger1) on table1 will be execute by RDBMS, then
trigger1 will insert a new record into datalogger which describes
the action event is "inserted", table name is "table1", and the
inserted record id is "new_recordId" as example. The same process
need to be applied for modifying action.
- On your application, create a job, which will try to query the datalogger table periodically, (1ms, 10ms,... as your requirement)
to find is there a new record in that table, if any, read the new
record and find out what happened with your database based on the
new record (determine by time or auto-increment id,..)
Related
Im trying to create a DSS service that can insert Order / Order details data.
It looks like standard task so I guessing there should be some 'best practice solution'
So in transaction mode insert new row in parent table, get a new row ID and send it in insert statement for populating child table... In a case of failure roll back the whole transaction ..
Can someone suggest where should I start or point to some resources ?
Thanks
You can user Query Result Export feature to export the rowID after querying a select query to get the rowID and pass that to populate child tables
I have a live table in dynamo with about 28 million records in it.
The table has a number of GSI that I'd like to change to be LSIs however LSIs can only be created when the table is created.
I need to create a new table and migrate the data with minimum downtime. I was thinking I'd do the following:
Create the new table with the correct indexes.
Update the code to write records to the old and new table. When this starts, take a note of the timestamp for the first record.
Write a simple process to sync existing data for anything with a create date prior to my first date.
I'd have to add a lock field to the new table to prevent race conditions when an existing record is updated.
When it's all synced we'd swap to using the new table.
I think that will work, but it's fairly complicated and feels prone to error. Has anyone found a better way to do this?
Here is an approach:
(Let's refer to the table with GSIs as oldTable and the new table with LSIs as newTable).
Create newTable with the required LSIs.
Create a DynamoDB tirgger for the oldTable such that for every new record coming to the oldTable insert the same record to the newTable. (This logic needs to be in the AWS Lambda).
Make your application point to the newTable.
Migrate all the records from oldTable to newTable.
I refactored a table that stored both metadata and data into two tables, one for metadata and one for data. This allows metadata to be queried efficiently.
I also created an updatable view with the original table's columns, using sqlite's insert, update and delete triggers. This allows calling code that needs both data and metadata to remain unchanged.
The insert and update triggers write each incoming row as two rows - one in the metadata table and one in the data table, like this:
// View
CREATE VIEW IF NOT EXISTS Item as select n.Id, n.Title, n.Author, c.Content
FROM ItemMetadata n, ItemData c where n.id = c.Id
// Trigger
CREATE TRIGGER IF NOT EXISTS item_update
INSTEAD OF UPDATE OF id, Title, Author, Content ON Item
BEGIN
UPDATE ItemMetadata
SET Title=NEW.Title, Author=NEW.Author
WHERE Id=old.Id;
UPDATE ItemData SET Content=NEW.Content
WHERE Id=old.Id;
END;
Questions:
Are the updates to the ItemMetadata and ItemData tables atomic? Is there a chance that a reader can see the result of the first update before the second update has completed?
Originally I had the WHERE clauses be WHERE rowid=old.rowid but that seemed to cause random problems so I changed them to WHERE Id=old.Id. The original version was based on tutorial code I found. But after thinking about it I wonder how sqlite even comes up with an old rowid - after all, this is a view across multiple tables. What rowid does sqlite pass to an update trigger, and is the WHERE clause the way I first coded it problematic?
The documentation says:
No changes can be made to the database except within a transaction. Any command that changes the database (basically, any SQL command other than SELECT) will automatically start a transaction if one is not already in effect.
Commands in a trigger are considered part of the command that triggered the trigger.
So all commands in a trigger are part of a transaction, and atomic.
Views do not have a (usable) rowid.
I am using a global application user account to access database A. This user account does not have permissions to modify database A's schema (ie, create tables, modify tables, etc). This user also has access to database B, but only views. I need to run SQL to feed data from a view in database B into a table in database A.
In a perfect world, I would be able to use this SQL:
create database_a.mytable as (select * from database_b) with no data
However, the user can't create tables in database A. If I could get the DDL of the select statement then I could log in under my personal account (which doesn't have any access to database B) and run the DDL in database A to create the table.
The only other option is to manually write the SQL, but I don't want to do that, especially since this view I am wanting to copy has many columns of varying data types and sizes.
Edit: I may be getting closer. I just experimented with this:
show (select * from database_b.myview)
However, it generated the DLL of every single table that is used in the view itself, as well as the definition for the view. This doesn't really help me since I just want the schema of the select statement itself. In other words, I need what would be generated if I were to use the create table as statement mentioned above.
Edit for Rob: Perhaps "DDL" was the wrong term to use. Using show view db.myview just shows the definition of the view, not the schema it represents. In my above example of create table as, I show how you can create a table that mimics the schema of a result set returned in a select. It generates a DDL on the back end for creating a table and then executes that DDL to actually create the table. You can then say show table db.newtable and see the new table's DDL. I want to get that DDL directly from a select statement so that I can copy it, log out of the app account, into my personal account, and then execute the DDL to create the table.
This is only to save me the headache of having to type out the DDL manually by hand to save time and reduce typing errors, especially since the source view has so many columns. That said, I think hitting up the DBA or writing some snazzy stored procedure to do dynamic stuff would be a bit over the top for my needs. I think there has to be a way to get the DDL for creating a table schema directly from a select statement.
Generate DDL Statements for objects:
SHOW TABLE {DatabaseB}.{Table1};
SHOW VIEW {DatabaseB}.{View1};
Breakdown of columns in a view:
HELP VIEW {DatabaseB}.{View1};
However, without the ability to create the object in the target database DatabaseA your don't have much leverage. Obviously, if the object already existed INSERT INTO SELECT ... FROM DatabaseB.Table1 or MERGE INTO would be options that you already explored.
Alternative Solution
Would it be possible to have a stored procedure created that dynamically created the table based on the view name that is provided? The global application account would simply need privilege to execute the procedure. Generally the user creating the stored procedure would need the permissions to perform the actions contained within the stored procedure. (You have some additional flexibility with this in Teradata 13.10.)
There are some caveats with this approach. You are attempting to materialize views that could reference anywhere from hundreds to billions of records. These aren't simple 1:1 views that are put on top of the target tables. Trying to determine the required space in the target database to materialize the view will be difficult. Performance can and will vary depending on the complexity of the view and the data volumes. This will not be a fast-path or data block optimized operation.
As a DBA, I would be concerned with this approach being taken on by a global application account without fully understanding the intent. I trust you have an open line of communication with the DBA(s) involved for supporting this system. I'm sure there are reasons for your madness that can't be disclosed here.
Possible Solution - VOLATILE TABLE
Unless the implicit privilege for CREATE TABLE has been revoked from the global application account this solution should work.
Volatile tables do not require perm space. There table definitions persist for the duration of the session and any data inserted into them relies on the spool space of the user who instantiated it.
CREATE VOLATILE TABLE {Global Application UserID}.{TableA_Copy} AS
(
SELECT *
FROM {DatabaseB}.{TableA}
)
WITH NO DATA
NO PRIMARY INDEX
ON COMMIT PRESERVE ROWS;
SHOW TABLE {Global Application UserID}.{TableA_Copy};
I opted to use a Teradata 13.10 feature called NO PRIMARY INDEX. By default, CREATE TABLE AS will take the first column of the SELECT statement and make it the PRIMARY INDEX of the table. This could lead to skewing and perm space issues in your testing depending on the data demographics. You can specify an explicit PRIMARY INDEX on your own as you understand the underlying data. (See the DDL manuals for details on the syntax if you're uncertain.)
The use of ON COMMIT PRESERVE ROWS for the intent of this example is probably extraneous. But in reality if you popped any data into that table for testing this clause would be beneficial in Teradata mode as the data would otherwise be lost immediately after the CREATE TABLE or any other data manipulation was performed against the volatile table.
I would like to monitor 10 tables with 1000 records per table. I need to know when a record, and which record changed.
I have looked into SQL Dependencies, however it appears that SQL Dependencies would only be able to tell me that the table changed, and not which record changed. I would then have to compare all the records in the table to find the modified record. I suspect this would be a problem for me as the records constantly change.
I have also looked into SQL Trigger's, however I am not sure if triggers would work for monitoring which record changed.
Another thought I had, is to create a "Monitoring" table which would have records added to it via the application code whenever a record is modified.
Do you know of any other methods?
EDIT:
I am using SQL Server 2008
I have looked into Change Data Capture which is available in SQL 2008 and suggested by Martin Smith. Change Data Capture appears to be a robust, easy to implement and very attractive solution. I am going to roll CDC on my database.
You can add triggers and have them add rows to an audit table. They can audit the primary key of the rows that changed, and even additional information about the changes. For instance, in the case of an UPDATE, they can record the columns that changed.
Before you write/implement your own take a look at AutoAudit :
AutoAudit is a SQL Server (2005, 2008) Code-Gen utility that creates
Audit Trail Triggers with:
Created, CreatedBy, Modified, ModifiedBy, and RowVersion (incrementing INT) columns to table
Insert event logged to Audit table
Updates old and new values logged to Audit table
Delete logs all final values to the Audit table
view to reconstruct deleted rows
UDF to reconstruct Row History
Schema Audit Trigger to track schema changes
Re-code-gens triggers when Alter Table changes the table
What version and edition of SQL Server? Is Change Data Capture available? – Martin Smith
I am using SQL 2008 which supports Change Data Capture. Change Data Capture is a very robust method for tracking data changes as I would like to. Thanks for the answer.
Here's an idea.You can have a flag on each table that every time a record is created or updated is filled with current datetime. Then when you notice that a record has changed set its flag to null again.Thus unchanged records have null in their flag field and you can query not null values to see which record has changed/created and when (and set their flags to null again) .