eps insider

0 */routing/device Hook */ #define netlink_unused 1/ * UNUSED number */#define NETLINK_USERSOCK 2/ * Reserved for user mode socket protocols */#define Netlink_firewall 3/ * Unused number, formerly Ip_queue */.....The advantage of NetLink's interaction with the kernel relative to other (IOCTL, etc.) user spaces is that with NetLink, the kernel can proactively transmit kernel data to the user, not just as a response to a user requ

the elem is judged. In addition, to determine the validity of the Elem is "! =", so that you can filter both null and undefined, but do not filter the integer number 0, if Elem is a numeric type, by letting the Elem add an empty string, the Elem is converted to a string.If!elem is true, that is, Elem can be converted to false, then the loop is skipped and the next loop is executed. This line of code is used to filter the empty string case. If Elem is an integer number 0, because it has been con

"WCF Technology Insider" translation 15:1th Part _ 3rd Chapter _ Message Exchange Mode, topology and choreography: Message topology, message orchestration and summary of this chapter Message topology The message topology describes how messages are sent between one or more senders and recipients. A message topology can describe a simple application-application connection, but it can also describe complex applications-enterprise connections. In subseq

a transaction commits, its update results are seen by other transactions. Can solve the dirty read problem.repeatedread: In a transaction, the result of reading the same data is always the same, regardless of whether there are other transactions to manipulate the data, and whether the transaction is committed. Can resolve dirty read, non-repeatable read.serialization: Transaction serialization execution, the highest isolation level, sacrificing the concurrency of the system. All problems with c

versioning) information, and so on. SQL Server allows users to create temporary tables for their own use, where the physical location of these temporary tables is tempdb. Note: Each time the SQL Server instance is restarted, the contents of the database are deleted and recreated as a copy of the model. Therefore, When you need to create objects for testing purposes, and you do not want to keep them in the database after testing is complete, you can usually create them in tempdb. Even if you for

the Orders table that are placed by the specified customer within the specified date range, and also takes the behavior affected by the query as an output parameter.View Code Tips: Stored procedures can encapsulate business logic processing, better control security (to help avoid SQL injection), and improve execution performance (reduce network traffic). (3) Trigger: A special stored procedure that, whenever a particular event occurs, invokes the trigger and runs its code. SQL S

segments, data written in parallel on each disk, but no redundancy, easy to loseRAID1 most reliable, 22 mirror, slow reading speedRAID5 (commonly used) also adds parity information when storing data, data and inspection are stored on each disk, one disk is broken, the disk can be recovered through the inspection information of other disks, and requires at least three disks.RAID10(commonly used) first do RAID1 and then do RAID0. Two is a set of groups within a group of backups, inter-group paral

,Options:Map[String,String],data:dataframe): Resolveddatasource = {Dataframtwriter Source:/*** Specifies the behavior when data ortable already exists. Options include:*- `Savemode.overwrite` : Overwrite the existing data.*- `Savemode.append` : Append the data.*- `Savemode.ignore` : Ignore the operation (i.e. no-op).*- `savemode.errorifexists`: Default option, throw an exception at runtime.** @since 1.4.0*/defMode(savemode:savemode): Dataframewriter = { This.Mode= SavemodeThis }Import Java.util

of space, greater than 255 bytes required 2 bytes of space. So the maximum amount of space for varchar (10) is 11 bytes, with 1 bytes to hold the character length.7.BINARY and varbinary: similar to char and varchar, binary and varbinary store binary strings, rather than character strings, which do not have the concept of a character set, sorting and comparison by binary values. N in BINARY (n) and varbinary (n) all represent byte lengths. The binary padding character is 0x00, and the char paddi

middle of multiple CTE separated by commas (,), as shown in the following SQL statement:With Cte1 as ( select * FROM table1 where name like ' abc% '), Cte2 as ( select * from table2 where ID >), c Te3 as ( 3. If the expression name of the CTE is the same as a data table or view, the SQL statement immediately following the CTE is still using the CTE, of course, the following SQL statementThe data table or view is used, as shown in the following SQL statement:With Table1 as ( sele

the value 1, just set the Sql_mode parameter:SET Sql_mode='no_unsigned_subtraction ';Try not to use data that the Unsigned,int type may not hold, and int UNSIGNED may not be able to store it, so it is better to promote the int type to the bigint type in the database design phase.2, ZerofillIs like a displayed property.ALTER TABLE COLUMN int (4) UNSIGNED Zerofill;After the column A has been modified, the data for the T-table is searched, and a different display appears:SELECT from 0001B:2You c

different connection pools) to process the task. The total cost of maintaining 128 to 128*4 threads is significant. The Caelus connection pool will significantly reduce the number of threads. connection multiplexing. for a MySQL instance above there are multiple schema scenarios. Connections to different schemas for existing connection pools are not reusable. Caelus can reuse different schema connections to improve performance. Excessive transaction instructions. in the case of a transa

4th Zhang Ziyi (query4.2.1 Exist predicate: UseTSQLFundamentals2008Select * fromSales.customers asCwhereC.country=N'Spain'Select * fromSales.customers asCwhereC.country=N'Spain' and exists(Select * fromSales.orders asOwhereO.custid=C.custid)Select * fromSales.customers asCwhereC.country=N'Spain' and not exists(Select * fromSales.orders asOwhereO.custid=C.custid)View Code4.3.2 Continuous Gathering andSelect object_id('Sales.ordertotalsbyyear')if object_id('Sales.ordertotalsbyyear') is no

null but count does not.4.having5.select clauseIn this example, there are two function year repeats, but SQL internally recognizes duplicate functions and only calls onceThe select query does not guarantee that the returned data is a collection, which is guaranteed to be unique, and can be used distinctSeveral disadvantages of using asterisk *, A. Can only be returned in the default column order of the table, which can cause problems when the table is modified by the client by column index. B.

removal mechanism, I am still not very clear, is to go back to the buffer, or directly disappear; and, after the rollback operation, The size of the data file does not change, whether it can be false, the physical space has been allocated, and did not recover in time for the next reuse. The commit operation, which is done in a very short time, is possible because the operation simply removes the transaction ID information from the data page on the disk and is OK. Well, take a rigorous experimen

StatementINSERT into dbo. Orders (OrderID, OrderDate, Empid, CustID) EXEC@country='France ';SELECT into statementSELECT OrderID, OrderDate, Empid, CustID into dbo. Orders from TSQLFundamentals2008.Sales.Orders;The SELECT into statement copies the underlying structure of the source table (including column names, data types, whether null and identity attributes are allowed), and data. Constraints, indexes, and triggers are not copied from the source table.BULK INSERT statementBULK INSERTDbo.

SELECTOrderID, CustID, Empid, OrderDate, RequiredDate, ShippedDate, ShipperID, freight, ShipName, shipaddress, ShipCity, ShipRegion, Shippostalcode, ShipCountry fromsales.ordersWHERECustID= @cid;GOUse this function:SELECT OrderID, CustID from Dbo.fn_getcustorders (1 as CO;SummarizeTable expressions can simplify code, improve code maintainability, and encapsulate query logic. When you need to use table expressions, you use a derived table or a CTE if you do not plan to reuse their definitions,

. EmployeesINTERSECTSELECTrow_number () Over(PARTITION bycountry, region, CityORDER by(SELECT 0), country, region, City fromSales.customers;Execution Result:Note In the above SQL, using order by in the over clause of the sort function (select withIntersect_all as( SELECTrow_number () Over(PARTITION bycountry, region, CityORDER by(SELECT 0)) asrownum, country, region, City fromHR. EmployeesINTERSECT SELECTrow_number () Over(PARTITION bycountry, region, CityORDER by(SELECT 0), cou

When a client sends an INSERT instruction, how does it react internally to a table of the InnoDB type? This article will be for everyone to uncover this insider. Of course, I caishuxueqian, if you find something wrong, can point out, we discuss together.Suddenly find it difficult to explain the process in words, then use a picture instead of it, but more clear. The question I have not figured out is: The write time of Bin_log, the commit operation cor

UPSYesUninterruptiblePowerSupplyWhich is what we often callUPSUninterrupted power supply. CommonUPSThere are three types of power supplies: Online Interactive, online-only, and backup. EPSEmergency power supply system isEmergency Power SupplyIs an