database - What lock type is used in READ COMMITTED isolation level? -

-

I have found a contradiction in a Wikipedia article and it is not certain where the fault is (or maybe I do it correctly Does not understand).

According to the level of isolation:

"In the level of this separation, lock-based concurrency control holds the DBMS implementation write locks (acquisition of selected data) / Strong> By the end of the transaction, but when the selection is conducted, the reading locks are released (hence the non-recurring reading event can be at this isolation level, as discussed below Is) "

Also read further Read level Rtibddh isolation:

Transaction 1: 

  select * from users where id = 1;

Transaction 2: 

  The age of SET users = 21 where ID = 1 is updated; COMMIT;

Transactions 1: 

  Select * From users where id = 1; COMMIT;

According to the first quote, a write-up lock should be taken after the first selection statement in 1 transaction. How to successfully write another transaction lock can get locked and committed if this lock type is considered exclusive? Does DBMS really keep the locks written on selected data?

Wikipedia is incorrect in two ways:

  1. This is an implementation description is. An RDBMS does not have to do this. Using snapshot isolation can be implemented at least without lock to read.
  2. I do not know that RDBMS receives writing locks for reading. This sentence is unclear.

Comments

Post a Comment

Popular posts from this blog

java - org.apache.http.ProtocolException: Target host is not specified -

-
I have written a simple httprequest / response code and I am getting this error below: I used to type in my classpath httpclient, httpcore, common -Codecs and general logging. I am very new to Java and I do not know what's going on here. Please help me. code: import org.apache.http.client.HttpClient; Import org.apache.http.client.methods.HttpGet; Import org.apache.http.HttpResponse; Import org.apache.http.impl.client.HttpClientBuilder; Import org.apache.http.Header; Import org.apache.http.HttpHeaders; Public class UnshorteningUrl {public static zero main (string [] args throws exception {HttpGet request = zero; HTTP Client Client = HTTP ClientBuilder.credit (). Build (); Try {Request = New HTTP Gate ("trib.me/1lBFzSi"); HttpResponse httpResponse = client.execute (request); Header [] header = httpResponse.getHeaders (HttpHeaders.LOCATION); // Preconditions.checkState (headers.length == 1); String new url = header [0] .getValue (); System.out.println ("new url...
Read more

java - Gradle dependencies: compile project by relative path -

-
Is it possible to specify a dependency on another gradeal project in the granular (in android studios) outside the current project limits? For example, with a relative path like this: dependence {collection project ('../../ stdlib / dagger'}} MyApp (path / user / foo / workspace / mypad) The app (Path / User / Foo / Workspace / MyPass / App) And I have an Android Library Project with 3 subdomules: stdlib (path is / user / foo / Utilities (Path / User / Foo / Workspace / Stadlib / Utilis) http (Path / User / Foo / Workspace / Stadlib / HT) / Li> What I have to do is compile the Dagger, Util, http module in the MyApp project. The Stidelib Library module under heavy development And MyApp will grow in the form of Growth, so I do not want to push them into a Mewen repository. I am a little change. is likely to add another Gredle projects in some way? I will push the study library into the Maven repository after the source is in search of a temp...
Read more

ruby on rails - Object doesn't support #inspect when used with .include -

-
So I have participated in a glitch error that I do not even know how to debug. I am very new to the railing, so it has kicked my ass well when I use the .includes (school) seen by the student, it gives a blue box error, But when I look at any other model and .includes (school) , the school works just fine. class student & lt; ActiveRecord :: Base has has_many: relationships, foreign_key: "liker_id", dependent :: has_many: matches, foreign_key: "student_1_id", dependent :: deleted belong_to: school belong_to: conference belong_to: would_you_rather belong_to: home city belong_to: year is_to: Major and class school & lt; on the console activatecord :: Affiliate for the base: conference includes: respondent, class: "school", foreign_key: "rival_id" (e.g. For: School) Select SQL generated Select "School". * "School" from "school" "ID" IN (1) error message back NoMethodError: u...
Read more