Queries not running sql server book pdf enough? Tired of the phone calls from frustrated users? The book is revised to cover the very latest in performance optimization features and techniques. It provides the tools you need to approach your queries with performance in mind.
You’ll learn to be proactive in establishing performance baselines using tools like Performance Monitor and Extended Events. Reproduction of site books is authorized only for informative purposes and strictly for personal, private use. 1989 – and extends to the current day. The RTM version is 14. Two additional editions provide a superset of features not in the original Express Edition. The compact edition is an embedded database engine. It is limited to 4 GB maximum database size and cannot be run as a Windows service, Compact Edition must be hosted by the application using it.
5 version includes support for ADO. Starting early 2016, Microsoft made this version free of charge to the public. It can also be used as an embedded database. HP base on the Fast Track architecture. 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.
Initially designed and developed by Sybase Inc. A page is marked with a 96-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: data stored in the database, index, allocation map which holds information about how pages are allocated to tables and indexes, change map which holds information about the changes made to other pages since last backup or logging, or contain large data types such as image or text. A row in a database table cannot span more than one page, so is limited to 8 KB in size.
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. 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. Any 8 KB page can be buffered in-memory, and the set of all pages currently buffered is called the buffer cache. 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. 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.
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. 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. The mechanism allows a new version of a row to be created whenever the row is updated, as opposed to overwriting the row, i.
ID of the transaction that created the 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. It is processed by the query processor, which figures out the sequence of steps that will be necessary to retrieve the requested data. There might be multiple ways to process the same query. It then decides which sequence to access the tables referred in the query, which sequence to execute the operations and what access method to be used to access the tables.