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following is a simple example showing the effect of using this hint, example T-SQL as shown in Listing 1:
SELECT * from
[adventureworks].[ Sales]. [SalesOrderDetail] A
INNER JOIN [Sales]. SalesOrderHeader B on
A.salesorderid=b.salesorderid
Code Listing 1.
The statement does not go in parallel by default and the execution plan is shown in Figure 1:
Figure 1.
Let's add a hint to the statement below, as shown in Listing 2.
SELE
we use a undocument query prompt directly to the statement, forcing the parallel cost threshold for the query to be dropped to 0, forcing the statement to go in parallel, and the statement execution time from 20 seconds to 5 seconds (note: Use a hash join hint for 7 seconds).
The following is a simple example showing the effect of using this hint, example T-SQL as shown in Listing 1:
SELECT * from
[adventureworks].[ Sales]. [SalesOrderDetail] A
I
on the statement, which causes the parallel cost threshold of the query to be reduced to 0, which forces the statement to go parallel and the statement execution time from 20 seconds to 5 seconds (note: Using the hash join hint is 7 seconds). The following is a simple example of the effect of using this hint, as shown in Listing 1 of the sample T-sql: SELECT *FromINNER JOIN [Sales]. SalesOrderHeader b on A.salesorderid=b.salesorderid Code Listing 1.T
Tags: style case requires tab something 2DX SRV union simpleWork often encounter very difficult data queries, operators do not know how your database tables are designed, and do not know what data your database records, he only know what data they need to see, even some of the data does not exist at all. Difficulty of single-table query: A table of database tables, such as a room two people games, homeowner Houser challenger Challenger, only recorde
Partii:sql BasicsCHAPTER 4Creating a simple Querydescribes a way to create SQL the technology of the statement -- "Request/translation/clean up/sql "The SELECT operationin SQL can broken down into three smaller operations,Which we'll referto as the select statement,the Select expression,and the SelectQuery.The first layer contains one layer , nesting with each o
pre_11g_enable_capture=TRUE SCOPE=BOTH;Mon Jun 23 19:40:44 2008DBMS_WORKLOAD_CAPTURE.START_CAPTURE(): Starting database capture at 06/23/2008 19:40:44. . .
Because I am capturing an Oracle 10gR2 database, I set the dynamic initialization parameter PRE_11G_ENABLE_CAPTURE to TRUE before starting the capture.Load generation: to simulate parallel execution of similar code for different users, I have prepared a shell script 10gSI_RandomLoadGenerator.sh), which is similar to the shell script
Database optimization tutorial (I) preface definition of slow query, and introduction of database optimization tutorial
Preface
Recently, I helped the company optimize the database. Based on what I learned, I used the learning knowledge step by step in practice, and finally I got the speed up, it takes only three seconds for a query to be executed for more than one minute.
I will summarize what I have lea
: set the virtual memory size to at least three times the physical memory installed on the computer. Configure the SQL Server max server memory Server configuration option to 1.5 times the physical memory (half the virtual memory size ). 7. Increase the number of server CPUs. However, you must understand that resources such as memory are more required for concurrent processing of serial processing. Whether to use parallelism or serial travel is autom
Database optimization tutorial (I) preface definition of slow query, and introduction of database optimization tutorial
Preface
Recently, I helped the company optimize the database. Based on what I learned, I used the learning knowledge step by step in practice, and finally I got the speed up, it takes only three seconds for a query to be executed for more than one minute.
I will summarize what I have lea
requires resources such as memory. The use of parallel or string travel is the MSSQL automatic evaluation option. A single task is decomposed into multiple tasks and can be run on the processor. For example, delays in sorting, connecting, scanning, and group by words are performed simultaneously, and SQL Server determines the optimal level of parallelism based on the load of the system, and complex
IntroductionThe SQL language is an easy-to-learn yet powerful language that allows you to quickly get started and write more complex query statements. But for most developers, using SQL to query a database does not have an abstract process and a reasonable step, which is likely to be "stuck" when writing specific SQL q
SQL language is a simple but powerful language that allows you to quickly get started and write more complex query statements. But for most developers, using SQL to query a database doesn't have an abstract process and a reasonable step, this is likely to lead to a "card" when writing specific SQL query statements to s
database will faint.In addition, execution plans can be reused, and the simpler SQL statements are more likely to be reused. Complex SQL statements have to be re-parsed as long as one character changes, and then the bulk of the garbage is stuck in memory. It is conceivable how inefficient the database will be.4. Staging intermediate results using temporary table
service to perform full-text indexing and querying, consider: Configure the virtual memory size to be at least 3 times times the physical memory installed on the computer. Configure the SQL Server max server memory server configuration option to 1.5 times times the physical memory (half of the virtual memory size setting). 7. Increase the number of server CPUs, but it is important to understand that parallel processing of serial processing requires r
time taken by event execution: 58.2706 s
Response time:
Min: 0.95 ms
Avg: 5.83 ms
Max: 68.36 ms
Approx. 95 percentile: 9.42 ms
Threads fairness:
Events (avg/stddev): 312.5000/47.80
Execution time (avg/stddev): 1.8210/0.02
4.3 supplement as a comparison, we added a multi-field index containing the attract_tp, column_id, field2, and status fields on MySQL. the qps measured is more than 4000, which is still inferior to PostgreSQL. It can be seen that the simple query performance of MySQ
memory size to at least three times the physical memory installed on the computer. Configure the SQL Server Max Server Memory server configuration option to 1.5 times the physical memory (half the virtual memory size ). 7. Increase the number of server CPUs. However, you must understand that resources such as memory are more required for concurrent processing of serial processing. Whether to use parallelism or serial travel is automatically evaluated
Label:Hibernate returns the processing of result sets using native SQL queries Today is OK, see the company framework there is a native SQL write function, said really before I did this thing, but for a long time no use, have forgotten almost, and now basically use the HQL statement to query the results. Hibernate uses Createsqlquery to implement
is complete.
Isolation (Isolation): All concurrent transactions that modify data are isolated from each other.
persistence (Durability): After a transaction completes, its effect on the system is permanent.
3. Create a transactionStatements that manage transactions in T-sql:
Start transaction: BEGIN TRANSACTION
COMMIT TRANSACTION: Commit Transaction
ROLLBACK TRANSACTION: ROLLBACK TRANSACTION
virtual memory size to be at least 3 times times the physical memory installed on the computer. Configure the SQL Server max server memory server configuration option to 1.5 times times the physical memory (half of the virtual memory size setting).7. Increase the number of server CPUs, but it is important to understand that parallel processing of serial processing requires resources such as memory. The use of parallel or string travel is the MSSQL au
practice, the WHERE clause uses values that depend on an external factor, such as QueryString, session, or user input in a control on the page, and so on. Typically, we specify these inputs by using parameters. In Microsoft SQL Server, parameters are in the form of @parametername, such as:
1SELECT ProductName 2FROM Products 3WHERE UnitPrice > @Price
For SELECT, INSERT, UPDATE, and DELETE statements, SqlDataSource supports their parameterized
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