identify poor performance in sql server

columns are frequently accessed at the same time, and each column contains duplicate values. You can consider creating a composite index;③ Composite indexes should try to overwrite key queries, and the leading column must be the most frequently used column.2. is null and IS NOT NULLNull cannot be used as an index. Any column containing null values will not be included in the index. Even if there are multiple columns in the index, as long as one of these columns contains null, this column will b

are: not,! =, 10. Use Delete sparinglyIn general, some of the logic of deleting data will be implemented more or less in stored procedures. For a small number of tables, the problem is not very big. But for large data tables, deleting data with delete can have a certain effect on the performance of the stored procedure. Because delete takes a full table-by-scan approach, it is a transactional operation that is counted into the

Unlike other SQL Server databases, tempdb stops at SQL Server and automatically drops and re-create upon restart. by default, a new 8 MB (MDF file: 8 MB; LDF file: 1 MB, autogtouth is set to 10%) recovery model is a simple tempdb database. After the tempdb database is created, DBA can create data objects, temporary

not necessarily the true inner join:SELECT A.* FROM A INNER JOIN B ON A.KEY=B.KEYMay or may not require party B to be in the execution plan based on what constraints exists. If A.key is an empty foreign key reference B.key, then the optimizer cannot from it must confirm that a B row exists, and each row is scheduled to fall B. If A.key is a mandatory foreign key reference B.key, then the optimizer is free to guarantee the existence of the line from the constraints of the plan to reduce B. Howev

example, the following example uses the pubs database. SELECT au_id, au_lname, au_fname from authors WHERE au_lname = ' White ' The indexes established on the following columns will be useful indexes for the optimizer ? au_lname ? au_lname, au_fname The indexes that are built on the following columns will not work well for the optimizer ? au_address ? au_fname, au_lname Consider using narrow indexes on one or two columns, narrow indexes are more efficient than multiple indexes and composite ind

target_recovery_time = [number of seconds or minutes]As mentioned earlier, SQL Server analyzes the current system pressure and, when it considers that there is no need to checkpoint at this time, kills the process, thus preventing the disk subsystem from becoming worse. When checkpoint is throttled, it is recorded in the information of the Sleep_bpool_flush wait type.Under normal circumstances, this wait s

A Introduced Some "super users" with access to data have learned professional Transact-SQL. The convenience of the Report Builder in SQL Server 2005 Report Services (SSRS) extends to the creation of powerful Transact-SQL queries, making it easier for more users to use it. Their ability to consume system resources is b

Because SQL Server 2000 lacks some high-end performance, it is considered a 90-pound little. In fact, no strong person can accomplish every feat, and no company needs every high-end feature. For years, many large and small businesses have been using SQL Server to run their c

compression is 167M, the size of the table after compression is only 40% of the original table, the effect is obvious, and because most of the table's fields are only IDs, the relative repetition value is not too much.However, we see that the size of the index varies substantially, so we continue to compress the index:5. Compression indexAlter index idx_tb_wcb_id on Tb_wcbrebuildwith (Data_compression=row)6, the comparison after the index compressionsp_spaceused ' ms_visit_qst_opt '/*name

SQL Server performance optimization -- wait -- SLEEP_BPROOL_FLUSHPreface: There is a database for historical archiving (referred to as the historical database). After a certain amount of time, the data file has reached more than 700 GB, and it was decided that some data does not need to be retained, this part of data is truncate and more than 600 GB of space is a

: here, both have been positioned to occupy One of the CPUs high in SQL , which can combine the efficiency of business scenarios and SQL , and whether communication with developers such as/DBA is optimized or how to optimize (By the way, it is suggested that the amount of data in the database will have a large impact on the performance gap, this test, 10W of

, however, it is very likely that a page stores five data records. Because a column has one or two more bytes, only four data records can be stored. You may think that there is nothing to save one piece of data, but after the data volume is very large, there will be significant performance differences between 4 pieces of data and 5 pieces of data on one page. The reason for storing more data on a page is not to save storage costs, but the hard disk is

occupied storage space. In actual applications, this extreme situation is rare, however, it is very likely that a page stores five data records. Because a column has one or two more bytes, only four data records can be stored. You may think that there is nothing to save one piece of data, but after the data volume is very large, there will be significant performance differences between 4 pieces of data and 5 pieces of data on one page. The reason for

of addition, subtraction, multiplication, division, the following summary -------------------------------------------- Here is just an extreme example. As a result, a byte deviation is caused to double the occupied storage space. In actual applications, this extreme situation is rare, however, it is very likely that a page stores five data records. Because a column has one or two more bytes, only four data records can be stored. You may think that there is nothing to save one piece of data, but

When installing SQL Server 2003 Development edition and Enterprise Edition on Windows Server 2000, Windows XP, or Windows 2008, the "performance counter registry Configuration unit consistency" check will fail (Windows Server 2008 has not been tested due to no environment cu

fragmentation has occurred? Execute the following SQL statements in your database. (Sql2005 or earlier database, replace the database name "adventureworks") Select object_name (DT. object_id) tablename, Si. nameindexname, DT. avg_fragmentation_in_percent asexternalfragmentation, DT. avg_page_space_used_in_percent asinternalfragmentationfrom (select object_id, index_id, avg_fragmentation_in_percent, avg_page_space_used_in_percent from sys. dm_db_index

smallertable (Lookupcolumn) Look at the query execution plan for both At this point we see the above query execution plan, we can clearly see the left JOIN .... Is null or full JOIN then after filtering, just after creating the index performance improved a little, but unlike the left JOIN ... Is null for not exists the planned execution is different from not creating an index, at this point the flow aggregation is used first and then the right half

What is database partition?Database partitioning is a type of horizontal table segmentation. This technology is provided by SQL Server 2005 Enterprise Edition and later SQL Server versions. This type of horizontal table segmentation is different from that in SQL

I. Preface Index plays an important role in database performance. The advantages and disadvantages of index design directly affect the efficiency of DB execution. Therefore, when performing DB tuning, some of them will start to process the index. SQL server also provides a good tool for Database Engine Tuning Advisor and provides some advice on index creation and

perform it during idle time on the server. after repeated tests, after, the server maintenance job has not run yet, and the user has been off duty, even if each contraction is 100 GB, it only takes more than one hour. Despite the unsatisfactory results, readers may want to see how to solve the problem thoroughly. However, it is a formal environment and cannot be easily tried or modified. However, in additi