The 3. NET Synchronization Services. Starting early , Microsoft made this edition free of charge to the public. Evaluation SQL Server Evaluation Edition, also known as the Trial Edition, has all the features of the Enterprise Edition, but is limited to days, after which the tools will continue to run, but the server services will stop. Intended for use as an application component, it did not include GUI management tools. Later, Microsoft also made available a web admin tool.
Had workload or connection limits like MSDE, but no database size limit. Includes standard management tools. It supports logical processors and virtually unlimited memory and comes with StreamInsight Premium edition. TDS is an application layer protocol, used to transfer data between a database server and a client.
Initially designed and developed by Sybase Inc. Consequently, access to SQL Server is available over these protocols. SQL Server supports different data types, including primitive types such as Integer, Float, Decimal, Char including character strings , Varchar variable length character strings , binary for unstructured blobs of data , Text for textual data among others.
The rounding of floats to integers uses either Symmetric Arithmetic Rounding or Symmetric Round Down fix depending on arguments: In addition to tables, a database can also contain other objects including views , stored procedures , indexes and constraints , along with a transaction log. A SQL Server database can contain a maximum of objects, and can span multiple OS-level files with a maximum file size of bytes 1 exabyte.
Secondary data files, identified with a. Log files are identified with the. A page is marked with a byte header which stores metadata about the page including the page number, page type, free space on the page and the ID of the object that owns it. Page type defines the data contained in the page: A database object can either span all 8 pages in an extent "uniform extent" or share an extent with up to 7 more objects "mixed extent".
The partition size is user defined; by default all rows are in a single partition. A table is split into multiple partitions in order to spread a database over a computer cluster. Rows in each partition are stored in either B-tree or heap structure.
If the table has an associated, clustered index to allow fast retrieval of rows, the rows are stored in-order according to their index values, with a B-tree providing the index. The data is in the leaf node of the leaves, and other nodes storing the index values for the leaf data reachable from the respective nodes. If the index is non-clustered, the rows are not sorted according to the index keys. An indexed view has the same storage structure as an indexed table.
A table without a clustered index is stored in an unordered heap structure. However, the table may have non-clustered indices to allow fast retrieval of rows.
In some situations the heap structure has performance advantages over the clustered structure. Both heaps and B-trees can span multiple allocation units. The amount of memory available to SQL Server decides how many pages will be cached in memory. The buffer cache is managed by the Buffer Manager. Either reading from or writing to any page copies it to the buffer cache. Subsequent reads or writes are redirected to the in-memory copy, rather than the on-disc version.
The page is updated on the disc by the Buffer Manager only if the in-memory cache has not been referenced for some time. Each page is written along with its checksum when it is written. When reading the page back, its checksum is computed again and matched with the stored version to ensure the page has not been damaged or tampered with in the meantime. As such, it needs to control concurrent access to shared data, to ensure data integrity—when multiple clients update the same data, or clients attempt to read data that is in the process of being changed by another client.
SQL Server provides two modes of concurrency control: When pessimistic concurrency control is being used, SQL Server controls concurrent access by using locks.
Locks can be either shared or exclusive. Exclusive lock grants the user exclusive access to the data—no other user can access the data as long as the lock is held. Shared locks are used when some data is being read—multiple users can read from data locked with a shared lock, but not acquire an exclusive lock. The latter would have to wait for all shared locks to be released.
Locks can be applied on different levels of granularity—on entire tables, pages, or even on a per-row basis on tables. For indexes, it can either be on the entire index or on index leaves. The level of granularity to be used is defined on a per-database basis by the database administrator. While a fine-grained locking system allows more users to use the table or index simultaneously, it requires more resources, so it does not automatically yield higher performance.
SQL Server also includes two more lightweight mutual exclusion solutions—latches and spinlocks—which are less robust than locks but are less resource intensive.
SQL Server also monitors all worker threads that acquire locks to ensure that they do not end up in deadlocks —in case they do, SQL Server takes remedial measures, which in many cases are to kill one of the threads entangled in a deadlock and roll back the transaction it started. The Lock Manager maintains an in-memory table that manages the database objects and locks, if any, on them along with other metadata about the lock.
Access to any shared object is mediated by the lock manager, which either grants access to the resource or blocks it. SQL Server also provides the optimistic concurrency control mechanism, which is similar to the multiversion concurrency control used in other databases. The mechanism allows a new version of a row to be created whenever the row is updated, as opposed to overwriting the row, i. Both the old as well as the new versions of the row are stored and maintained, though the old versions are moved out of the database into a system database identified as Tempdb.
When a row is in the process of being updated, any other requests are not blocked unlike locking but are executed on the older version of the row. If the other request is an update statement, it will result in two different versions of the rows—both of them will be stored by the database, identified by their respective transaction IDs. The query declaratively specifies what is to be retrieved.
It is processed by the query processor, which figures out the sequence of steps that will be necessary to retrieve the requested data. How are SQL Server licenses sold? The software licensing options remains the same for SQL Server as previously available e. Table 1: The major benefit of this option is that there is no requirement to try to quantify the number of users or devices accessing the SQL Server, be that direct or via indirect means multiplexing. When running SQL Server in a physical environment, licenses must be assigned to all of the physical cores on the server.
A minimum of four core licenses per physical processor are required, with licenses being sold in packs of two. So how many licenses do I need? The process to determine this is relatively straight forward: Ascertain how many cores there are per processor keeping in mind the minimum requirement of four cores per processor Count the total number of cores A total of twelve cores are present, therefore 6 SQL Server Per Core licenses packs of 2 are required Example 1 The Per Core option is often the preferred licensing option when: VM1 will therefore require four core licenses VM2 has six virtual cores A total of eight cores are present, but four are required for VM1 therefore bringing the count up to ten virtual cores, so 5 SQL Server Per Core licenses packs of 2 are required Example 2 Note: The following will need to be identified: It is recommended that you engage your Software reseller to determine which option best suits your SQL Server requirements factoring in server role, access, technical requirements etc.
Some use cases to be aware of As we have touched on here, there are a number of different licensing models available for SQL Server depending on the scenario and use case.
Choose either LocalDB or Express depending on your needs above. Use this if you already have for further migration path details. Plus, SQL Server will enable new with in-memory built in across all for your virtualization and cloud computing data platform from on-premises to cloud. SQL Server will provide mission-critical performance, hybrid cloud solutions, with an easy onramp and a complete and consistent needs. Licensing editions Compare features in all simple way to create and work with databases from code. How can I buy core-based licensing for the Business Intelligence Edition. When will these changes take effect. The CAL requirement is waived for. Please refer to the Product List the database and only need the. Use this if you need Where to buy MS SQL Server 2014 Standard editions to determine the ideal solution management tools.
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