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  • Best way to run multiple queries per second on database, performance wise?

    - by Michael Joell
    I am currently using Java to insert and update data multiple times per second. Never having used databases with Java, I am not sure what is required, and how to get the best performance. I currently have a method for each type of query I need to do (for example, update a row in a database). I also have a method to create the database connection. Below is my simplified code. public static void addOneForUserInChannel(String channel, String username) throws SQLException { Connection dbConnection = null; PreparedStatement ps = null; String updateSQL = "UPDATE " + channel + "_count SET messages = messages + 1 WHERE username = ?"; try { dbConnection = getDBConnection(); ps = dbConnection.prepareStatement(updateSQL); ps.setString(1, username); ps.executeUpdate(); } catch(SQLException e) { System.out.println(e.getMessage()); } finally { if(ps != null) { ps.close(); } if(dbConnection != null) { dbConnection.close(); } } } And my DB connection private static Connection getDBConnection() { Connection dbConnection = null; try { Class.forName(DB_DRIVER); } catch (ClassNotFoundException e) { System.out.println(e.getMessage()); } try { dbConnection = DriverManager.getConnection(DB_CONNECTION, DB_USER,DB_PASSWORD); return dbConnection; } catch (SQLException e) { System.out.println(e.getMessage()); } return dbConnection; } This seems to be working fine for now, with about 1-2 queries per second, but I am worried that once I expand and it is running many more, I might have some issues. My questions: Is there a way to have a persistent database connection throughout the entire run time of the process? If so, should I do this? Are there any other optimizations that I should do to help with performance? Thanks

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  • Why would using a Temp table be faster than a nested query?

    - by Mongus Pong
    We are trying to optimise some of our queries. One query is doing the following: SELECT t.TaskID, t.Name as Task, '' as Tracker, t.ClientID, (<complex subquery>) Date, INTO [#Gadget] FROM task t SELECT TOP 500 TaskID, Task, Tracker, ClientID, dbo.GetClientDisplayName(ClientID) as Client FROM [#Gadget] order by CASE WHEN Date IS NULL THEN 1 ELSE 0 END , Date ASC DROP TABLE [#Gadget] (I have removed the complex subquery, cos I dont think its relevant other than to explain why this query has been done as a two stage process.) Now I would have thought it would be far more efficient to merge this down into a single query using subqueries as : SELECT TOP 500 TaskID, Task, Tracker, ClientID, dbo.GetClientDisplayName(ClientID) FROM ( SELECT t.TaskID, t.Name as Task, '' as Tracker, t.ClientID, (<complex subquery>) Date, FROM task t ) as sub order by CASE WHEN Date IS NULL THEN 1 ELSE 0 END , Date ASC This would give the optimiser better information to work out what was going on and avoid any temporary tables. It should be faster. But it turns out it is a lot slower. 8 seconds vs under 5 seconds. I cant work out why this would be the case as all my knowledge of databases imply that subqueries would always be faster than using temporary tables. Can anyone explain what could be going on!?!?

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  • Select rows in random order and then reverse it

    - by Faruz
    I need to select rows in random order and return a query which holds the rows in both regular order and in reverse order. This is done to simulate a fantasy draft for a basketball game I'm working on. For example, I need a result set as followed: team1 1 team2 2 team6 3 team9 4 team9 5 team6 6 team2 7 team1 8 As you can see, the first four teams are random then then following four are in reverse order. Hope I managed to explain the problem, if not - please comment and I'll explain further.

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  • making a combined sum of two columns

    - by bsandrabr
    I have a table (apples) containing: cid date_am date_pm ---------------------- 1 1 1 2 2 1 3 1 3 1 1 2 I asked a question earlier (badly) about how I would rank the customers in order of the number of ones(1) they had. The solution was (based on one column): SELECT cid, sum( date_pm ) AS No_of_ones FROM apples WHERE date_am =1 GROUP BY cid ORDER BY no_of_ones DESC This works great for one column but how would I do the same for the sum of the two columns. ie. SELECT cid, sum( date_pm ) AS No_of_ones FROM apples WHERE date_am =1 add to SELECT cid, sum( date_am ) AS No_of_ones FROM apples WHERE date_pm =1 GROUP by cid ORDER by no_of_ones(added) hope I've managed to make that clear enough for you to help -thanks

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  • Why is Postgres doing a Hash in this query?

    - by Claudiu
    I have two tables: A and P. I want to get information out of all rows in A whose id is in a temporary table I created, tmp_ids. However, there is additional information about A in the P table, foo, and I want to get this info as well. I have the following query: SELECT A.H_id AS hid, A.id AS aid, P.foo, A.pos, A.size FROM tmp_ids, P, A WHERE tmp_ids.id = A.H_id AND P.id = A.P_id I noticed it going slowly, and when I asked Postgres to explain, I noticed that it combines tmp_ids with an index on A I created for H_id with a nested loop. However, it hashes all of P before doing a Hash join with the result of the first merge. P is quite large and I think this is what's taking all the time. Why would it create a hash there? P.id is P's primary key, and A.P_id has an index of its own.

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  • Having different database sorting order (default_scope) for two different views

    - by Juniper747
    In my model (pins.rb), I have two sorting orders: default_scope order: 'pins.featured DESC' #for adding featured posts to the top of a list default_scope order: 'pins.created_at DESC' #for adding the remaining posts beneath the featured posts This sorting order (above) is how I want my 'pins view' (index.html.erb) to look. Which is just a list of ALL user posts. In my 'users view' (show.html.erb) I am using the same model (pins.rb) to list only current_user pins. HOWEVER, I want to sorting order to ignore the "featured" default scope and only use the second scope: default_scope order: 'pins.created_at DESC' How can I accomplish this? I tried doing something like this: default_scope order: 'pins.featured DESC', only: :index default_scope order: 'pins.created_at DESC' But that didn't fly... UPDATE I updated my model to define a scope: scope :featy, order: 'pins.featured DESC' default_scope order: 'pins.created_at DESC' And updated my pins view to: <%= render @pins.featy %> However, now when I open my pins view, I get the error: undefined method `featy' for #<Array:0x00000100ddbc78> UPDATE 2 User.rb class User < ActiveRecord::Base attr_accessible :name, :email, :username, :password, :password_confirmation, :avatar, :password_reset_token, :password_reset_sent_at has_secure_password has_many :pins, dependent: :destroy #destroys user posts when user is destroyed # has_many :featured_pins, order: 'featured DESC', class_name: "Pin", source: :pin has_attached_file :avatar, :styles => { :medium => "300x300#", :thumb => "120x120#" } before_save { |user| user.email = user.email.downcase } before_save { |user| user.username = user.username.downcase } before_save :create_remember_token before_save :capitalize_name validates :name, presence: true, length: { maximum: 50 } VALID_EMAIL_REGEX = /\A[\w+\-.]+@[a-z\d\-.]+\.[a-z]+\z/i VALID_USERNAME_REGEX = /^[A-Za-z0-9]+(?:[_][A-Za-z0-9]+)*$/ validates :email, presence: true, format: { with: VALID_EMAIL_REGEX }, uniqueness: { case_sensitive: false } validates :username, presence: true, format: { with: VALID_USERNAME_REGEX }, uniqueness: { case_sensitive: false } validates :password, length: { minimum: 6 }, on: :create #on create, because was causing erros on pw_reset Pin.rb class Pin < ActiveRecord::Base attr_accessible :content, :title, :privacy, :date, :dark, :bright, :fragmented, :hashtag, :emotion, :user_id, :imagesource, :imageowner, :featured belongs_to :user before_save :capitalize_title before_validation :generate_slug validates :content, presence: true, length: { maximum: 8000 } validates :title, presence: true, length: { maximum: 24 } validates :imagesource, presence: { message: "Please search and choose an image" }, length: { maximum: 255 } validates_inclusion_of :privacy, :in => [true, false] validates :slug, uniqueness: true, presence: true, exclusion: {in: %w[signup signin signout home info privacy]} # for sorting featured and newest posts first default_scope order: 'pins.created_at DESC' scope :featured_order, order: 'pins.featured DESC' def to_param slug # or "#{id}-#{name}".parameterize end def generate_slug # makes the url slug address bar freindly self.slug ||= loop do random_token = Digest::MD5.hexdigest(Time.zone.now.to_s + title)[0..9]+"-"+"#{title}".parameterize break random_token unless Pin.where(slug: random_token).exists? end end protected def capitalize_title self.title = title.split.map(&:capitalize).join(' ') end end users_controller.rb class UsersController < ApplicationController before_filter :signed_in_user, only: [:edit, :update, :show] before_filter :correct_user, only: [:edit, :update, :show] before_filter :admin_user, only: :destroy def index if !current_user.admin? redirect_to root_path end end def menu @user = current_user end def show @user = User.find(params[:id]) @pins = @user.pins current_user.touch(:last_log_in) #sets the last log in time if [email protected]? render 'pages/info/' end end def new @user = User.new end pins_controller.rb class PinsController < ApplicationController before_filter :signed_in_user, except: [:show] # GET /pins, GET /pins.json def index #Live Feed @pins = Pin.all @featured_pins = Pin.featured_order respond_to do |format| format.html # index.html.erb format.json { render json: @pins } end end # GET /pins, GET /pins.json def show #single Pin View @pin = Pin.find_by_slug!(params[:id]) require 'uri' #this gets the photo's id from the stored uri @image_id = URI(@pin.imagesource).path.split('/').second if @pin.privacy == true #check for private pins if signed_in? if @pin.user_id == current_user.id respond_to do |format| format.html # show.html.erb format.json { render json: @pin } end else redirect_to home_path, notice: "Prohibited 1" end else redirect_to home_path, notice: "Prohibited 2" end else respond_to do |format| format.html # show.html.erb format.json { render json: @pin } end end end # GET /pins, GET /pins.json def new @pin = current_user.pins.new respond_to do |format| format.html # new.html.erb format.json { render json: @pin } end end # GET /pins/1/edit def edit @pin = current_user.pins.find_by_slug!(params[:id]) end Finally, on my index.html.erb I have: <%= render @featured_pins %>

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  • reset all logged in users after they shutdown their consoled

    - by gin
    i have list of student who have Nintendo DSs, and they should log in my website to solve some sheets (by using DS Opera browser), when they logged in , (status filed at my DB will change from 0 to 1),also the status change to 0 if they log out, what i need is when the student didn't log out and Shut down their DS's , the status should be 0,, i don't have an idea to it, any suggestion would be helpful for me .. FYI ,DS opera browser limitation here

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  • Alternative to subqueries

    - by Juanma
    I'm using Mysql 5.1, and have this query, is there a way to not use the subqueries and accomplish the same result? SELECT oref.affiliate_id, ROUND(sum( oph.amount ) * 0.10 ,2) AS tsum FROM operators_referer AS oref LEFT JOIN operators_payments_history AS oph ON oref.operator_id = oph.operator_id WHERE oref.affiliate_id = 28221 AND ( oph.date_paid > ( SELECT MAX(aph.date_paid) FROM affiliates_payments_history AS aph WHERE aph.operator_id = oref.affiliate_id ) OR ( SELECT MAX(aph.date_paid) FROM affiliates_payments_history AS aph WHERE aph.operator_id = oref.affiliate_id ) is NULL )

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  • How to merge existing row with new data in SQLite?

    - by CSharperWithJava
    I have a database full of simple note data, with columns for title, due date, priority, and details. There is also a _id column PRIMARY KEY int. Say I have a note in the table already with some data filled and the rest null. I also have a set of data that will fill all those fields. Is there a way that I can only write data to the fields that are NULL? I can't overwrite existing data, but I'd like to add data to NULL columns. I know the rowId of the target row. If my target row had rowId of 5, I could do something like this: UPDATE SET duedate='some date', priority='2', details='some text' WHERE _id=5 But that would overwrite all the data in that row, and I don't want to lose any data that might be there. How can I change this statement to avoid writing to non-null fields?

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  • i tried to implement tde in sql2008...n got the error below.....plz help me to resolve...

    - by mahima
    while using USE mssqltips_tde; CREATE DATABASE ENCRYPTION KEY with ALGORITHM = AES_256 ENCRYPTION BY SERVER CERTIFICATE TDECert GO getting error Msg 156, Level 15, State 1, Line 2 Incorrect syntax near the keyword 'KEY'. Msg 319, Level 15, State 1, Line 3 Incorrect syntax near the keyword 'with'. If this statement is a common table expression or an xmlnamespaces clause, the previous statement must be terminated with a semicolon. please help in resolving the same as i need to implement Encryption on my DB

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  • How to write contents of a rails database to external file

    - by user1296787
    I'm trying to have rails send the contents of my database to an external textfile. I wanted this done everytime a new user is created. However, when i try to do the following in my user.rb model file, before_save :write_data def write_data() File.open("data.txt", "w") do |myfile| myfile.write(User.all) end end It doesn't write the actual contents of the database, instead, it displays something like this User:0x109858540 Can anyone help? Thanks.

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  • mySQL: Order by field size/length

    - by Sadi
    Here is a table structure (e.g. test): __________________________________________ | Field Name | Data Type | |________________|_________________________| | id | BIGINT (20) | |________________|_________________________| | title | varchar(25) | |________________|_________________________| | description | text | |________________|_________________________| A query like: SELECT * FROM TEST ORDER BY description; But I would like to order by the field size/length of the field description. The field type will be TEXT or BLOB.

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  • Aggregate Functions in Index with IBMDB2

    - by Erkan
    Is there any way to pre aggregate results of aggregate functionts (f.i. count()) and store it in an index? The background is: i want to speed up count() queries. So that: Select count(users) from TE123 where region = 'A'; would be supported by an index like Region Count(Users) A 548 E 458 I know that MQTs would also help for this problem. However, in this case it is not possible to use MQT, as we use kind of an ORM and we don't want to define Entities on MQTs. I just slightly remember - one DBA told me - that there is such a function planned for DB2 V10.

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  • array insert in db

    - by gloris
    Hi, How best to put the array (100 or more length) in the database (MySQL)? I do not want multiple access to the database because it is so loaded. So my solution is as follows: string insert = "INSERT INTO programs (name, id) VALUES "; for(int i = 0; i < name.Length; i++) { if (i != 0) { insert = insert + ",("; } else { insert = insert + "("; } insert = insert + "'" + name[i] + "','" + id[i] + "'"; insert = insert + ")"; } //INSERT INTO programs (name, id) VALUES ('Peter','32'),('Rikko','343') .... But maybe is a faster version? Thanks

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  • Can't create a MySQL query that generates 4 rows for each row in the table it references.

    - by UkraineTrain
    I need to create a MySQL query that generates 4 rows for each row in the table it references. I need some of the information in those rows to repeat and some to be different. In the table each row stands for one day. I need to break the day up in 6 hour increments, hence the four rows for each entry. I need to create one column which for each day will have '12AM', '6AM', '12PM', and '6PM' values and another column will have the corresponding numeric values calculated for those entries. Thanks a lot in advance and I will really appreciate any help on this.

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  • How can I tell when a MySQL table was last updated?

    - by RaGE
    In the footer of my page, I would like to add something like "last updated the xx/xx/200x"; with this date being the last time a certain mySQL table has been updated. What is the best way to do that ? Is there a function to retrieve the date ? Should I make an access to the database everytime my footer is displayed ?

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  • Copy new records from datatable and identify changes in old records

    - by Betite
    Assume there are two tables: Remote_table and My_table. Remote_table has 6 columns: **PROJECT JOB_TYPE MONTH YEAR** HOURS IS_DELETED 134393 70 1 2013 30 0 134393 70 2 2013 50 0 134393 70 3 2013 80 0 134393 70 10 2012 10 0 134393 70 11 2012 0 0 134393 70 12 2012 15 0 My_table is a copy of remote_table. I tried to copy only the new records from the remote_table by this query: SELECT * FROM [remote_DB].[LudanProjectManager].[dbo].Remote_table EXCEPT SELECT * FROM My_table It works OK but I get a duplicate primary key exception when changes have been made on the remote_table on the hours column. Can anyone think of a way to copy only the new records from remote_table and if changes has been made on old records, to identify them and update the my_table to correspond?

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  • MySQL- complex data query in a single statement

    - by yoda
    Hi, Consider the following structure : Ignore the table user_token. Now, imagine that you need to get all the roles related to an user, wich may be through it's related groups or directly related to him. In case the same role appears related to a group and the user directly, the role related to the user will prevail over the role given by the group. Is there any chance this could be done in a single query? Cheers!

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  • Database concurrency issue in .NET application

    - by MC.
    If userA deleted OrderA while userB is modifying OrderA, then userB saves OrderA then there is no order in the database to be updated. My problem is there is no error! The SqlDataAdapter.Update succeeds and returns a "1" indicating a record was modified when this is not true. Does anybody know how this is supposed to work, thanks.

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  • How can i pull an image and data from a Database?

    - by user1851377
    I am trying to pull data from a Database using C#.net and use a Foreach loop to make it visible on a page. Every time i run the code i only get one item that shows up when i know that there is at least 7 items in the DB. i have placed the code below for the C#. SqlConnection oConnection = new SqlConnection(ConfigurationManager.ConnectionStrings["HomeGrownEnergyConnectionString"].ToString()); string sqlEnergy = "Select * from Product p where p.ProductTypeId=3"; SqlCommand oCmd = new SqlCommand(sqlEnergy, oConnection); DataTable dtenergy = new DataTable(); SqlDataAdapter oDa = new SqlDataAdapter(oCmd); try { oConnection.Open(); ; oDa.Fill(dtenergy); } catch (Exception ex) { lblnodata.Text = ex.Message; return; } finally { oConnection.Close(); } DataTableReader results = dtenergy.CreateDataReader(); if (results.HasRows) { results.Read(); foreach(DataRow result in dtenergy.Rows) { byte[] imgProd = result["ThumnailLocation"] as byte[]; ID.Text = result["ProductID"].ToString(); Name.Text = result["Name"].ToString(); price.Text = FormatPriceColumn(result["Price"].ToString()); } } Here is the code for the asp.net. <div> <asp:Image ID="imgProd" CssClass="ProdImg" runat="server" /> <asp:Label runat="server" ID="ID" /> <asp:Label runat="server" ID="Name" /> <asp:Label runat="server" ID="price" /> <asp:TextBox ID="txtQty" MaxLength="3" runat="server" Width="30px" /> <asp:Button runat="server" ID="Addtocart" Text="Add To Cart" CommandName="AddToCart" ItemStyle-CssClass="btnCol" /> If someone could please help me that would be great thanks.

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  • How to add user customized data to database?

    - by CSharperWithJava
    I am trying to design a sqlite database that will store notes. Each of these notes will have common fields like title, due date, details, priority, and completed. In addition though, I would like to add data for more specialized notes like price for shopping list items and author/publisher data for books. I also want to have a few general purpose fields that users can fill with whatever text data they want. How can I design my database table in this case? I could just have a field for each piece of data for every note, but that would waste a lot of fields and I'd like to have other options and suggestions.

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