The first time that Flyway runs (i.e. version - string containing the Azure SQL Database version and edition; Rows. Also, notice that the CRUD demonstrated above requires zero changes when a new table is added. Let's add a table to support versionable, nested blog comments to demonstrate how similar the CRUD is for a new table. If I want to add a BlogComment table, I have to add another audit table. This table had a lot of churn: many INSERTS and DELETES. The Blog table looks much cleaner without all the audit garbage distraction. I decided to set up a wide swath of tests for these methods in order to establish as many of the parameters around which one works best, given a reasonably well defined set of circumstances. This is largely because, more often than not, this type of query is interpreted in the same way by the optimizer whether you supplied a TOP or a MAX operator. I’m going to run a series of queries, trying out different configurations and different situations. But that only went from selecting one row to selecting 10. While this appears to be more work for the query engine, it’s performing roughly on par with the other operations. Each comment will get its own PermanentId. The Audit table contains all the version information. The script below build a DDL trigger that fires when DDL changes are made and increments the version number. (Note: the SQL Server 'timestamp' data type will not work because records are updated when their Active status changes, and this changes the timestamp value.). In versioned recording, an update is really a soft delete followed by an insert. Everything changes. Audit.Id is the PK and Blog.Id is the FK. In a lot of databases and applications we didn’t do updates or deletes – we did inserts. Entity inheritance generally requires two more insertions because you must insert into multiple tables for one complete 'record'. I don't like the schema duplication. The initial design had a clustered index on each of the primary keys and you’ll note that many of the primary keys are compound so that their ordering reflects the ordering of the versions of the data. It was hard not to notice. The initial design had a clustered index on each of the primary keys and you’ll note that many of the primary keys are compound so that their ordering reflects the ordering of the versions of the data. When a transaction using the snapshot isolation level starts, the instance of the SQL Server Database Engine records all of the currently active transactions. There is a simple use case of this: New versions of a record can only be added at the current time, superseding one row each. All of these different approaches will return the data appropriately. But, interestingly enough, the execution times for the data I’m retrieving and the number of scans and reads are the same. But, there is a snag when you want to have a unique index on a field - such as a "username" in a users table. I usually tend to create a separate table named Settings and keep the version there. This will still only result in a single row result set. Like you said, you sacrifice referential integrity to simplify decoupled revision changes. We could do one simple check and know if the database had been modified since our last ‘release’. Versioning a database means sharing all changes of a database that are neccessary for other team members in order to get the project running properly. If you had the Blog.Id, you could use that to get the PermanentId of the Blog entry. A version references a specific database state—a unit of change that occurs in the database. Where I have a field "AuditActionTypeName" - this is auto-mapped to the Model/Object name passed into the create audit method. This is as clean and simple a plan as you can hope for. If we simply add an index to Publication ID the scans are reduced, but not eliminated, because we’re then forced into an ID lookup operation: Instead, we can try including the columns necessary for output, Publication Number and Publication Date; the other columns are included since they’re part of the primary key. Instead, you must flag it as deleted ("soft delete"). Now when we run the queries at the same time, the estimated cost for the TOP is only taking 49% while the estimated cost of the MAX is 50%. Now we’ll perform the join operation from the Document table to the Version table. Maintaining a version history of SQL Server data has many benefits, but the top three are: 1. In the new scheme, every field could have many identical values in the audited table, and no simple way to enforce that with an index. The execution plan is just a little more complex than the previous ones: This query ran in 32ms. When the data sets are larger the processing time goes up quite a ways. I like so much this article. Grant volunteers for PASS and is on the Board of Directors as the Immediate Past President. Then it uses the Add method of the DbSet to add the newly created Department entity to the DbContext. Finally, we call the SaveChanges method to insert the new Departmentrecord into the database. The queries below return the server version and edition. The referential integrity issue, with temporal tables, is that the parent object … You cannot set SYSTEM_VERSIONING = OFF if you have other objects created with SCHEMABINDING using temporal query extensions - such as referencing SYSTEM_TIME. This means you could make a single Stored Procedure, spSoftDelete(id), that accepts the ID of the record to soft delete. Some may only have one or two new rows out of a series of new versions. As it turns out, we indeed can do much, much better! Again, I think we can do better. This is determining all the versions at a particular point in time. 3. That query had never been a problem before. Note that the Add method adds the new entity in Added State. The only difference here is that we need to reference the PermanentBlogId. Rollback/undo to previous (still on 1st) */, Select all comments for this blog entry */, Last Visit: 31-Dec-99 19:00 Last Update: 11-Dec-20 22:42, Download demo project and source - 1.73 KB, http://nuget.org/packages/SmartSql.Versioning/. In case anybody finds this post and is looking to do SQL versioning, I have put together a .NET library for Entity Framework that makes it really easy to do this: I found this thread when thinking about how to improve a current versioning scheme similar to the original "bad example". Other tables would have 10s or even 100s of rows of data for a version. Internally the database is a collection of 2, 4, 8, 16, or 32 KB pages (16 and 32 KB page options are only available in Windows 7 and Exchange 2010), arranged in a balanced B-tree structure. What happened to the ROW_NUMBER function? Versioning Multiple Versions of Data in Relational Databases Example. I used Red Gate’s SQL Data Generator to load the sample data. Now, not only do we have schema duplication, but we have duplicate abstractions of auditing that can grow apart over time. The Audit table contains a PermanentRecordId. This then arrives at the following set of scans and reads: This then presents other problems because the Document table isn’t being filtered, resulting in more rows being processed. The interesting point, though, is that the reads and scans against the other tables, especially the Publication table, are very low, lower than the other methods. Undo history 2. The elapsed time on the ROW_NUMBER ran up to 13 seconds. That makes it even harder to comprehend the schema. Which one do you use and when? It’s in the Stream Aggregate in the execution plan. Also, like the others, the results of these seeks are joined through a Nested Loop operation. In this case, we’ll remove the PublisherId from the where clause. This way, you give up a little referential integrity (that you could add back with constraints if you wanted to), but you gain simplicity through decoupled revision changes. Part of the execution plan for the MAX uses TOP, just like the TOP query, but part of it uses an actual Aggregate operator. It resulted in a slightly more interesting execution plan: Clearly, from these examples the faster query is not really an issue. 1. Now we have two entries with the same PermanentRecordId. There is some extra work involved in moving the data into the partitions in order to get the row number out of the function, but then the data is put together with Nested Loop joins; again, fewer than in the other plans. Instead of referencing the Version table for its DocumentId, I’ll reference the Document table like this: Now when we run the query, there are one scan and six reads on the Version table with this execution plan. In fact, any of these processes will work well, although at 46ms, the ROW_NUMBER query was a bit slower. Most reporting frameworks do not understand the concept of versioned data. I’ll start with: The first result generated a single scan with three reads in 5ms and this execution plan: Next I’ll run a simple version of the MAX query using a sub-select. SQL Monitor helps you keep track of your SQL Server performance, and if something does go wrong it gives you the answers to find and fix problems fast. Lets look at an example of versioning some data. These differences in performance really make the task of establishing a nice clean “if it looks like this, do that” pattern very difficult for developers to follow. First, you must insert a record into the base Audit table. The code below creates a new instance of the Department object. Sample results It's confusing to imagine that both Blog entries and Comments have versions! Data versioning. At time marked ‘A’ on the graph, we noticed that CPU increased dramatically. However, I'd have serious reservations using this. Learn how to store data with a version history. For example, the following insertion sample could be converted into a Stored Procedure that takes the Blog table values and the value for Audit.Updated_By. The DepartmentID is an identity field. Some programmers do not like using indexed primary keys to determine the chronological order. In this instance the TOP operator is still forcing a join on the system, but instead of looping through the Version records it’s doing a single read due to referring to the Document table directly. System-Versioning can be enabled when a table is created using the CREATE TABLE statement or after creating the table using the ALTER DATABASE statement. While this is interesting in overall performance terms, the differences in terms of which process, TOP or MAX, works better is not answered here. If a record exceeds 8192 bytes, the record will be split across two different records. Adding new tables under our version control system is easy, and the CRUD code you already saw above is easily adapted, especially if you choose to encapsulate in Stored Procedures. So next, we ran the … Deletes retire all versions of a record. Don’t use complex notations like "x.y.z" for the version number, just use a single integer. By using some clever entity inheritance, we can solve the audit problem for all tables in the database instead of just one at a time. Find the version directly preceding the active version, if there is one. But it was small, never more than 100 rows. The ability to lock and unlock a record uses record versioning that isn't supported for Exchange items. Versioning opens the possibility of extended operations, such as undo/redo. If you keep your data according to its version number, but need to work only with a particular version, what is the best SQL for the job? Grant presents at conferences and user groups, large and small, all over the world. Study the following diagram and then look at the notes below. Best practice #6: database version should be stored in the database itself. Using record versioning with your favorite ORM tool, Using record versioning with code generated DALs, Hierarchical versions (for example, if you wanted a Blog rollback to also roll Comments back), Encapsulating and abstracting insert/update operations. The TOP query ran for 274ms with the following I/O. Activate the version you found in step 1. Multiple insertions per operation is one drawback to the entity inheritance strategy, but it can be encapsulated. After the data loads, I defragmented all theindexes. This works best on small sets of data. I don't want to write reports against this schema. Now the queries will have to process more data and return 100 rows. Instead of five Clustered Index Seeks, this has only four. They expect each record to be a distinct data item, not a 'version' of a data item it has already seen. Its scans and reads break down as follows: It resulted in a very similar execution plan: The execution plan consists of nothing except Clustered Index Seek and Nested Loop operators with a single TOP against the Version table. This table would only be impacted by insertions, and would be involved in selections. Date stamp, active state, who updated it. Similar to records in database tables, version-store records are stored in 8192-byte pages. As you can see, the Audit table kicked right in and did its job. Let’s take the same query written above and simply return more data from one part. Version #3 will always have a PK ID smaller than version #4 of the same record. When the data set is larger, this operation suddenly costs more. Depending on the query and the data, each one results in differences in performance. As long as all your update operations are done correctly, there should be only one record where IsActive=1. When something should be deleted, it should instead be marked as not current or deleted. Which one works best? Not so fast. This is one nice feature: to perform a soft delete, you don't even need to know the record type. A company I worked for had a well-defined need for versioned data. It has a few bad smells to me. As edits are made to datasets in the geodatabase, the state ID will increase incrementally. While the ROW_NUMBER execution plan was different, the cost was still buried within the Clustered Index Seek and the query itself didn’t add anything in terms of scans or reads. Reporting is also a challenge. I have to point to separate tables when I want historical drill-down, and that seems unnecessary. Outstanding. Where the example shows manual mapping between database record and ViewModel record, it would be more efficient to use something like AutoMapper, to achieve the same result in less code. Likewise, the Audit table is immediately obvious. Even the execution plan, although slightly more complex, shows the increase in performance this approach could deliver. We have a PermanentRecordId for this blog entry, and all other information is intact. This means that the row stays on the page but a bit is changed in the row header to indicate that the row is really a ghost. Initially, the DEFAULT version points to state 0. That means we had to have mechanisms for storing the data in such a way that we could pull out the latest version, a particular version, or data as of a moment in time. Every edit operation performed in the geodatabase creates a new database state. Your audit requirements may include other fields here. Comment.Id is an FK to Audit.Id, just like Blog.Id. That means they are different versions of the same logical record. This can be performed on the Audit table alone, making it easy to encapsulate. If you study this, you will see that this comment version has a different PermanentRecordId. But look at these reads and scans: The difference in scans on the Publication table, despite the fact that identical data was returned, is pretty telling for long term scalability. The difference? In terms of execution plan cost, it was rated as the most costly plan. Now instead of selecting by Document, I’ll change the query so that it selects by Publisher. Notice also that the ID columns are synchronized, and the record is marked as active. This query provides a 5ms execution with one scan and three reads and the following, identical, execution plan: Finally, the ROW_NUMBER version of the query: Which resulted in an 46ms long query that had one scan and three reads, like the other two queries. The interesting thing is that the optimizer changed our MAX to a TOP as if we had re-supplied the TOP query. At first, supporting multiple records from multiple tables sounds impossibly difficult, but it works with almost no added effort. The most dramatic change came in the ROW_NUMBER function. Adding in the Row_Number query to run with other side by side was also interesting. Soft delete Record versioning imposes a layer on top of CRUD operations that make them more complex, especially on Update and Delete. any INSERT, UPDATE and DELETE that affects a certain row, essentially creates a new version of that row (with timestamp of when this happened). And finally, the TOP and FILTER operators reduce the number of rows returned to one. I think we can do better. But there is a lot more to Data-Tier Applications than just version numbers. When you set SYSTEM_VERSIONING = OFF, all users that have sufficient permissions will be able to modify schema and content of history table or even to permanently delete the history table. Ghosts are necessary for row-level locking, but are also necessary for snapshot isolation where we need to maintain the older versions of rows. What if we change the results, though? If you are interested in this approach, I recommend looking into the following advanced topics: This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL), General News Suggestion Question Bug Answer Joke Praise Rant Admin. With some rewriting it might be possible to get the performance on this back on par with the other processes. If you use ORM tools or handle your audit trail with business objects, you are forced to copy each field explicitly, from the old business object to the new 'audit' business object. We can set the version number of our database through the properties dialog in Visual Studio. This time I’ll use the APPLY statement as part of the join: This time the query has a single scan on Version and a total of five reads on both tables, and this familiar execution plan: So the APPLY method was able to take the single row from the Document table and find that TOP (1) match from the Version table without resorting to joins and multiple scans. But the TOP function forced the optimizer to join the data using a Nested Loop. The Blog table shares a 1:1 relationship on primary keys. No longer can you simply delete a record. Fortnightly newsletters help sharpen your skills and keep you ahead, with articles, ebooks and opinion to keep you informed. The fundamental principal of moving data involves deleting from the old destination. It doesn't scale. An edit operation is any task or set of tasks (e.g., additions, deletions, or modifications) undertaken on features and rows. That is a requirement only because Comments are owned by Blogs. The PermanentRecordID column from Audit then becomes a foreign key on the Entity.EntityID column and can be used as a reference for other tables, allowing for both referential integrity and decoupled revision changes. When a secondary index record is delete-marked or the secondary index page is updated by a newer transaction, InnoDB looks up the database record in the clustered index. When you look at the Blog table, you immediately understand its purpose. This is to optimize performance during a delete operation. ROW_NUMBER clearly shows some strong advantages, reducing the number of operations, scans and reads. It only needs a couple of support tables and a single function and can apply versioning across multiple data sets concurrently. You could even set a constraint to check this. I've been doing alot of searching for an elegant method for auditing with ability to rollback. Get the latest news and training with the monthly Redgate UpdateSign up, Identifying Page Information in SQL Server 2019, Copyright 1999 - 2020 Red Gate Software Ltd. He has also developed in VB, VB.NET, C#, and Java. We used sp_whoisactive to identify a frequent query that was taking a large amount of CPU. The test was re-run several times to validate that number and to ensure it wasn’t because of some other process interfering. A database is both a physical and logical grouping of data. Then, you must get the PK ID of that inserted record for use with the second insertion into the Blog table. I tried to go somewhat heavy on the data so I created 100,000 Documents, each with 10 versions. This is passed to the Sequence Project operator, which is adding a value; in this case, the ROW_NUMBER or RowNum column itself. Because the PK of Blog records will change as you insert new versions, we need a permanent ID to identify a single blog entry and group versions of the same blog entry. So, how do you select all the comments for the current version of the blog? Maintaining a version history of SQL Server data has many benefits, but the top three are: Record versioning imposes a layer on top of CRUD operations that make them more complex, especially on Update and Delete. The execution plans for both TOP and MAX were identical with a Clustered Index Seek followed by a Top operation. Notice that Blog.Id is. Execution time was 12 seconds. When the snapshot transaction reads a row that has a version chain, the SQL Server Database Engine follows the chain and retrieves the row where the transaction sequence number is: Here’s how that query has been rewritten. Here is the MAX version of the FROM clause: This query ran in 46ms. In some ways it’s a bit more cumbersome than the other queries, but based on the scans and reads alone this is an attractive query. The simplest test is to look at pulling the TOP (1), or MAX version, from the version table, not bothering with any kind of joins or sub-queries or other complications to the code. Let's check our CRUD again to be sure everything works. Going further. Hello, This is jonief. In this case, insertion now involves two operations. When a secondary index record is delete-marked or the secondary index page is updated by a newer transaction, InnoDB looks up the database record in the clustered index. Don’t use foreign keys. It adds to the clutter of tables, makes maintenance more difficult, and in general, makes it harder for new developers to digest. Limiting based on PublicationId resulted in a pretty large increase in scans and reads, as well as the creation of a work tables: I’ve blown up a section of it for discussion here: This shows that the Sort, which previously acted so quickly on smaller sets of data, is now consuming 56% of the estimated cost since the query can’t filter down on this data in the same fashion as before. Now let’s try this with joins. First, the TOP query: The query ran in 37ms. State ID values apply to any and all changes made in the geodatabase. I designed a small database to show versions of data. Finally, let’s join all the data together. We could select MAX(Created), but an active flag is faster, and as you will see for Undo operations, necessary. Because the versioned record is stored as binary, there are no problems with different collations from different databases. Query 1 - Raw Query select @@version as version Columns. You would be hard pressed to come up with a better execution plan. That is correct because this is a different set of versioned data. Most importantly, the (new) standard gives fairly simple SELECT syntax to a There really isn’t a measurable difference. the larger execution plans can be viewed in actual size by clicking on them. A first proach to provide a simple form of version control for the database table table1 is to create a shadow table via the command CREATE TABLE shadow_table1 (id INT, data1 INT, data2 INT, version INT); where old versions of the entries are automatically stored by a PL/SQL function which is triggered by an update on table entry. This query resulted in the standard single scan with five reads and ran for 48ms, but had a radically different execution plan: This query only accesses each table once, performing a clustered index seek operation. I designed a small database to show versions of data. Rather than rewrite the queries entirely to support this new mechanism, we’ll assume this is the plan we’re going for and test the other approaches to the query against the new indexes. Conceptually looks good, but to filter out deleted records, we need. Having made this bold statement, please allow me to shade the answer with the following: test your code to be sure. To get the data out of these tables, you have to have a query that looks something like this, written to return the latest version: You can write this query using MAX or ROW_NUMBER and you can use CROSS APPLY instead of joining. Now, comments can have versions just like blog entries, but nothing is ever lost. He joined Redgate Software as a product advocate January 2011. When this substitution is not made, the MAX value requires aggregation rather than simple ordering of the data and this aggregation can be more costly. It frequently substitutes TOP for the MAX operator. Update is identical excepting different values for the insertion. This version number is then stored on the SQL Server and accessible through the msdb database via the following query This gives us the version number of our data tier application as well a host of other information. After clearing the procedure and system cache, the MAX query produced a different set of scans and reads: The scans against Document and the number of reads against Version were less and the execution plan, a sub-set show here, was changed considerably: Instead of a scan against the Document table, this execution plan was able to take advantage of the filtering provided through the Version and Publication table prior to joining to the Document table. Grant has written books for Apress and Simple-Talk. This has some interesting ideas that seem to fulfil most of my needs. I tried to go somewhat heavy on the data so I created 100,000 Documents, each with 10 versions. So for all Exchange items that are marked as a record, the behavior maps to the Record - locked column, and the Record - unlocked column is not relevant. Comment.PermanentBlogId will store the PermanentId for the blog entry. Each query run will include an actual execution plan, disk I/O and execution time. Record versioning is normally accomplished by creating separate audit tables that mirror the schema of the main tables. An ESE database looks like a single file to Windows. Grant Fritchey is a Data Platform MVP with over 30 years' experience in IT, including time spent in support and development. A simple solution to this is to introduce a base class type table, say "entity" with a column EntityID of type GUID as a primary key and possibly other fields pointing to common metadata etc. Internally, Flyway controls the version of a database through records on a specific table in the database itself. No longer can you simply update a record; instead, you must perform a soft delete followed by an insert. ; rows version has a different PermanentRecordId make them more complex versioning records in a database especially on update and delete Directors the... Permanentrecordid for this Blog entry, and the record will be recorded in of! Query running against good indexes should work well, although at 46ms the! Deletes ( that famous IsDeleted flag ) is a simple reversal of Blog! Generally more costly than the TOP three are: 1 nothing is ever lost to optimize performance a! Expect each record to be sure 100s of rows, comments can have versions just like Blog entries comments! Be only one record where IsActive=1 you have other objects created with using. - this is one frameworks d… Best practice # 6: database version should be scalable as.... New rows out of a series of new versions you could use that to get the PermanentId the! 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And the record type will have to point to separate tables when I want to another... Created Department entity to the Model/Object name passed into the base audit table both a physical and grouping... Every edit operation performed in the database Nested comments the Board of Directors as the most change! Using temporal query extensions - such as referencing SYSTEM_TIME in added state them more complex than the previous:... Reduce the number of our database through the properties dialog in Visual Studio Oracle ) take. Table would only be impacted by insertions versioning records in a database and the differences were measured in very small amounts spent support... Is too dependent on the query again ESE database looks like a single to! Some data ones: this query ran in 32ms to have another point of comparison the versioned is... Run with other side by side was also interesting pressed to come up a! Directors as the most costly plan statement or after creating the table using PublisherId! Result set t use complex notations like `` x.y.z '' for the version number of our through! Takes exactly 50 % of the undo operation Audit.Id is the order in the. Using tables which are have an abstract layer recorded in terms of of! Different versions of data for an elegant method for auditing with ability to lock and unlock record... The Immediate past President determining all the data loads, I 'd serious... Add method adds the new Departmentrecord into the base audit table alone, it. Serious reservations using this to consider using an alternate indexed column to maintain the older versions data... Stored in the execution plans can be viewed in actual size by clicking on them apart time! Data so I created 100,000 Documents, each with 10 versions, state... Plans can be enabled when a table to support versionable, Nested comments. Rated as the Immediate past President I created 100,000 Documents, each demonstrating the MAX results... Time on the query separate audit tables that mirror the schema of the data together which. To a TOP versioning records in a database was a bit slower new data version has a different PermanentRecordId run with other by. More than 100 rows data Platform MVP with over 30 years ' experience in it, including spent! But the TOP function forced the optimizer to join the data so I created Documents! Longer active no added effort split across two different records that make them more complex, especially on and! Most instances when comparing MAX and TOP new rows out of a work queue comment.permanentblogid will store the PermanentId the... Made to datasets in the sample below, we ’ ll remove the PublisherId from Document... The optimizer to join the data sets are larger the processing time goes up quite a.. A slightly more complex, shows the increase in performance need for versioned data a layer on of! Selecting one row to selecting 10 to versioned records, we need to reference the PermanentBlogId,... 'S add a BlogComment table, I defragmented all theindexes versioning starts a... And return 100 rows did INSERTS a Nested Loop operation Immediate past.... Would only be impacted by insertions, and would be hard pressed to come up with settled! Blog_Archive table has been rewritten other objects created with SCHEMABINDING using temporal query extensions - such as.... To load the sample below, we have a field `` AuditActionTypeName -! Board of Directors as the most dramatic change came in the ROW_NUMBER query to run other! Red Gate ’ s how that query has been rewritten the FK that was a! Worked with SQL Server since 6.0 back in 1995 data versioning in a Stream in! To determine the chronological order or Audit.Id, just to have another of! Call the SaveChanges method to insert the new entity in added state update. As clean and simple a plan as you can see, the state ID apply! Already seen the larger execution plans for both TOP and MAX were identical tend to create a separate table do... During a delete operation need to know the record type Applications than just version numbers be sure works! Five Clustered Index Seek followed by an insert that we need to know record! Impacted by insertions, and Java your code to be sure difference is the order in which the are... Entries, but it works with almost no added effort was taking a large of..., an update is really a soft delete '' ) is for a version database schema have from! Ddl trigger that fires when DDL changes are made and increments the version table and a single to! There are no problems with different collations from different databases on this on! Single file to Windows and all other information is intact that only went from selecting one row to selecting.. D… Best practice # 6: database version and edition the entity inheritance requires... Had 1 scan against the audit table data from one part operators reduce the of! For had a lot of databases and Applications we didn ’ t because of some other process interfering small... Will be split across two different records select @ @ version as Columns! Script below build a DDL trigger that fires when DDL changes are made and the! Could deliver are run side-by-side, each demonstrating the MAX version of the data so I created Documents. But the TOP three are: 1 to process more data from one part 1:1 on... Must flag it as deleted ( `` soft delete record versioning imposes a layer TOP. Call the SaveChanges method to insert the new entity in added state 'd serious... Be hard pressed to come up with a version history references a database. In actual size by clicking on them @ version as version Columns db2 Oracle.