Posts Tagged ‘New Features’

In my previous post we had discussed about column store index (non clustered), after 2 years in Microsoft’s new version SQL 2014 they have introduced the clustered column store index. The main limitation of the column store indexed tables were ready only (it was not apt for OLTP database), in the latest version Microsoft has introduced clustered column store index with eliminating data manipulation restriction.

Let us discuss how Microsoft achieved this feature.

Delta storage (Insert):  The data insert operations are costly in case of column store index, to over come the scenario SQL has introduced this new storage space called Delta storage. In delta store data would be stored as a traditional method (row store method) and data would be moved column store method using a mechanism called tuple mover. Tuple mover is mechanism that runs like a job in every 5 minutes and move all the rows to column store index without taking the table offline. Delta store is not used  in case of bulk insert.

The tuple mover waits delta storage to reach a limit of 1048576 rows, if the delta storage reached this number of rows the particular delta store would be closed and that would be ready to move column store index. If tuple mover finds a delta storage like this, tuple mover pull data from the storage and compress the data and then move to column store index. Mean while data can be inserted to another available delta storage so this process can be performed online.

Delete Bitmap(Delete) : To perform a efficient delete from column store index is a hard task, to over come SQL has introduced a segment called Delete bitmap this contains the information of deleted rows. When user requests for rows SQL retrieve records which are not exist in Delete bit map. So basically there is no changes happened in column store index when delete operations perform and the deleted data exist in the index pages. Index pages are get refreshed only when we rebuild or tuple mover.

Update : We have already discussed about how delete and insert works in column store indexes,for update SQL uses both delete and insert operations. SQL delete existing row using delete bit map method (virtual delete) and insert rows to the delta stores as usual insert operation. When next time select request for the row, delete bit map hides the old row and show the new row from Delta store.

ColumnStore2014_01

Now we have understood how the insert delete operations are taking place in column store index, in SQL 2014 we can create only one column store index on a table.

This is another interesting feature which Microsoft has introduced as part SQL 2016 release. We had traditional methods like magic tables and CDC to audit and log the history of a table, with the introduction of this feature Microsoft is bringing up new detailed feature called temporal tables. note this is not replacement for CDC, this feature help to track the life span of each row in a table.

Temporal means “relating to time” – all we are going to log is life span of each record. If you enable the property on a table, SQL will create a version table and your each row history would be kept in the newly created table. So with this feature I can easly identify that there was a row exist with these values in a particular time.

Temporal_01

In the above screenshot you can see the create statement on the top of the query window, the statement is as same as we use to create table. But to enable the property we should mention WITH(SYSTEM_VERSIONING = ON) to create a history table and also we have to add 2 more extra columns to store the life span of each record(starttime  and endtime).

In the above example I have created a table named TestTemporal, since the system version property is on, SQL creates a history table as shown in the figure. The history table contains the same number of columns and the history being stored in this table.

As shown in the picture I have inserted 2 rows to the table and updated a row and also deleted one of them, after these operations I have selected my TestTemporal and it’s history table. In the history table’s result we can see the old inserted and deleted record with the period those records were present in the main table. In the main table record end time is showing as infinite because the record is still exist in the table.

temporal_Drop

Now let discus about design changes on a version-ed table, if you create a table system version property on, you will not be able to delete of change the table definition without changing the property of the table. If you change the version-ed table to normal table, the history table will be converted to a normal table, once we revert back normal table to version table then a new history table will be created.

Hope you understand the feature, please do leave your comments.

Watch Demo to know more about temporal tables.

This is the one of the coolest feature I have seen while going through new features of SQL 2016. When we analyze performance of a query, we always seek help of actual execution plan. But the main disadvantage I have seen for actual execution plan is “We have to wait until query completes”, if the query took 10 minutes we have to wait till that time to see the details of the query.

After the arrival of Live query statistics, Microsft has over come the issue. now with this new feature in SQL 2016 will provide you a real time experience of execution plan while running a query. The new execution plan would show which part of the predicate is being used at a point of time.

The below screen shot shows the preview of a query plan

2016_Preview

note : The above picture is a merged one to show both tool bar and query execution , tool bars would be disabled while query running.