smartnet levels

: Use the primary key (primary key) and index as criteria to query. Do not use join. Do not use aggregate functions (aggregation). Perform heavy queries (housekeeping queries) only in replicas (replica), such as Business Intelligence (BI), data exploration, and so on, as far as possible, not on the main library (master database). We're going to dive into another blog about live migration (live migrations) and Application layer transactions (applicative transactions).

PostgreSQL two types of transaction isolation levels:Read Committed: The default isolation level in PostgreSQL. When a transaction runs at this isolation level, a select query can see only the data that was committed before the query was started and never see uncommitted data or changes made by other parallel transaction commits while the query was executing. If two transactions are being updated on the same tuple, the second update transaction waits for the first update transaction to commit or

blocked.PchangefilterstructAn option that points to the CHANGEFILTERSTRUCT structure pointer."Return value"If the function succeeds, the return value is a value other than 0.If the function fails, the return value is zero. To get information about the extended error, call GetLastError.egRestrictions for canceling low-privileged programs from sending messages to high-privilege programsBOOL bRes = Changewindowmessagefilterex (M_hwnd, Wm_copydata, Msgflt_allow, NULL);------------------------------

PHP programmers have eight levels of problem-solving capabilities. The eight levels of problem-solving ability of PHP programmers have been discussed. I personally think that the ability to solve problems ranks first in the interview, eight levels better than PHP programmers who can solve problems I have been talking about this topic. I personally think that th

2. transactions four isolation levels 1. If two threads are modified concurrently, They will be disruptive to each other , and the lock mechanism must be used to prevent concurrent modification of multiple threads. 2. If two threads are queried concurrently , There is no thread safety issue 3. If two threads a modification , a query ... will have 3 Types of questions: 1). Dirty reads : One transaction reads to another transaction UNCOMMITTED Dat

The following is from the third edition of High-performance MySQL, where understanding the acid of transactions and the four isolation levels helps us better understand the workings of the transaction.Here is a classic example of a banking application that explains the necessity of a transaction. If a bank's database has two tables: the cheque list (checking) and the savings Table (savings). Now to transfer $200 from the user Jane's chequing account t

data is a time snapshot of the source data, and when the user operation is complete, merge into the source data according to the point in time of each snapshotLock: The simplest implementation mechanism for concurrency control is the lock (not the lock mechanism used by MVCC).Read lock: Shared lock, by the read table operation plus the lock, lock the other users can only get the table or row of the shared lock, can not get exclusive lock, that is, can only read can not writeWrite Lock: An exclu

Tags: io ar using SP strong data on art issuesThe following is from the third edition of High-performance MySQL, where understanding the acid of transactions and the four isolation levels helps us better understand the workings of the transaction.Here is a classic example of a banking application that explains the necessity of a transaction. If a bank's database has two tables: the cheque list (checking) and the savings Table (savings). Now to transfe

execution of a transaction cannot affect the execution of other transactions, that is, the operation within one transaction and the data used are isolated to other transactions, and there is no interference between the concurrent execution of the transactions. Persistence (Durability): Once a transaction is committed, its changes to the database data are permanent. Subsequent operations should not have any effect on their execution results. 3. Isolation level of the transaction:The iso

Run Level level description0 All processes will be terminated, the machine will stop orderly, the system is at this runlevel when shutting down1 single-user mode for system maintenance with only a few processes running and all services not booting2 Multi-user mode, same as Run Level 3, only the network Questionnaire system (NFS) service does not start3 multi-user mode, allows multiple users to log on to the system, is the system's default boot level4 custom run

Six operating levels for Linux systems0 : is shutdown statusSystem shutdown mode, the system default operation level cannot be set to 0, otherwise it will not start normally, the machine shuts down.Scope of Use: Password loss can be entered into a single user level recover password1 : is a single-user stateRoot permissions for system maintenance, disable Telnet, just like Safe mode login under WindowsScope of Use: password loss can be entered into a

Log4j for me is always a Shing, basically is from other projects, or online to find a section down according to gourd painting scoop, anyway, are not insignificant things, never carefully studied. Recently done a small project, the customer to look at the log than the business is important, have to improve their own, carefully studied a bit, finally from the muddle out of the. This article does not intend to introduce the log4j in detail, so, such as log level (grade), Appender (output destinati

lock, T2 can only wait. T1 rollback Live Commit after releasing the row lock, T2 get lock, can read the data. However, the T2 session is not repeatable read, it is possible to read 200, and then T1 modified to 300,T2 read again, read the data is 300, how to avoid non-repeatable reading will be used to the next isolation level. Repeatable Read--repeatablereadYou can avoid non-repeatable reads, but there are phantom reads, and more records are read the second time. As follows: T1 locks th

In previous articles we have talked about several key aspects of URL rewrite. In the last article in this series, we'll discuss some of the details and characteristics of different levels of URL rewrite. In theory, the IIS-level URL rewrite is written in C or C + +, and is more performance-rewrite than asp.net-level URLs written using managed code. But I think the gap is negligible in most cases, and this performance is almost impossible to become a

the steps to automatically generate a table of contents using outline levels are as follows: Step one: Open the word2013 document, edit the contents of the body and need to be the contents of the TOC, then select the text as the title, right-click, select paragraph. Step two: In the pop-up Paragraph dialog box, select Set the outline level item to Level 1, and then click the OK button. Step three: Then, select the text you want as a level two d

Tags: height ABI ted data inconsistency update serialization attribute persistence commitAbout the ACID properties of the database has been a lot of introduction, here again summed up: A (atomicity) atomicity: That is, the transaction is either complete or not, do not appear only to do part of the situation, such as a to B transfer, do not appear a less money, B of the money did not increase the situation C ( Consistency) Consistency: Refers to the transaction from one state to another state is

Repeatable read in the same transaction, when the same query is made multiple times, a different result set is returned each time due to a transaction commit of another insert operation (insert).The standard repeatable read allows for Phantom reads, because this level only adds a shared lock on the read record, preventing other transactions from being modified, but does not prohibit others from inserting new data.When they first read, they are cured (snapshots), they can no longer find their own

Tags: how related executions Repeat locks other effects include statementsThe isolation level defines the behavior that is used to control the concurrency transaction, which determines how the data is locked when data is accessed and how it is isolated from other processes. Includes four levels, from high to Low: RR (Repeatable Read) RS (read stability) CS (cursor stability) UR (Uncommitted Read) 1.RR Isolation Level: Under this isolation level, DB2 l

This article transferred from: http://m.blog.csdn.net/article/details?id=51924963There are 4 isolation levels for database transactions, from low to high to read uncommitted, Read committed, Repeatable read, and Serializable. Also, dirty reads, non-repeatable reads, and Phantom reads can occur in concurrent operations of a transaction. The concepts and linkages are described below through case one by one.Read UNCOMMITTEDREAD UNCOMMITTED, as the name i

a transaction is committed, so it is not dirty to read, but the non-repeatable read problem can still occur: when a transaction reads the same data multiple times, because the commit of another transaction causes the data to change, the data that is read before and after is inconsistent.3. REPEATABLE READ (Repeatable Read)-this level avoids dirty reads and non-repeatable reads, but may have a virtual read problem: For example, A=1, transaction 1 changes it to 2, transaction 2 accesses to a=2, a