For questions about issues arising when multiple users or processes concurrently access or modify shared information in a database system.

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1answer
2k views

Show processlist / Max concurrent connections seem to max out at 131

When I put my database under a load test (basically just a basic write and basic read from our app), and run show processlist; in the middle of it, there is always 131 rows in the set and that's it. ...
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1answer
1k views

Differences between SQL Server 2005 and SQL Server 2008 deadlock handling

We recently upgraded a server to SQL Server 2008 R2. The server had been running SQL Server 2005. We are using Transactional Replication Management Data Warehouse and Data Collector on the ...
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1answer
74 views

Work queue with complex select and long processing: Ensuring concurrency

I have a queue table from which worker processes claim records, one at a time. It is crucial that no two workers claim same item to process. Normally this kind of thing is done with select top (1) ...
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0answers
171 views

High concurrency is even slower than low concurrency in mysql? [closed]

My application is supposed to handle high concurrency insert/update, now I have only one mysql instance setup for test. My application is full asynchronous, it should be able to handle 10,000 ...
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1answer
55 views

Patterns/Designs to help with concurrency/performance [closed]

I'm working on a SQL Server 2008 R2 DB and I'm experiencing some performance/concurrency issues with probably the main table in the DB. Problems like slow reads, deadlocks, poor performance in ...
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0answers
165 views

UPLOCK to avoid multiple reads

Given the following table structure... Orders ====== OrderId int PK OrderEvent =========== OrderEventId int PK OrderId int FK EventTypeId int FK I've got multiple concurrent processes SELECT-ing ...
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1answer
1k views

Why are timestamps not always increasing with concurrent inserts?

I'm seeing some unexpected behavior with timestamp (rowversion) columns . I created a test table: create table Test ( Test_Key int identity(1,1) primary key clustered, Test_Value int, ...
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1answer
29 views

Is reading a single record always an atomic operation?

Is reading a single record always an atomic operation? I mean, when e.g. a read (select) and write (update) query are simultaneously carried out on the same record, is it possible for the read ...
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2answers
1k views

How to maintain MySQL performance at high concurrency

The following has been observed using "mysqlslap". mysqlslap -u root -p --create-schema=matrix --query=monthly_kpi.sql --iterations=1 --concurrency=1 --delimiter=";" Benchmark Average number ...
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1answer
284 views

How to create fault tolerant databases? [closed]

I have a local application running on a LAN. Sometimes a database gets shutdown. In such a scenario how can I keep the application working? Can I have two concurrent databases so that one picks up the ...
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2answers
527 views

MySQL concurrent INSERTs

I have a MySQL database with InnoDB tables. There are different client processes making SELECT (to check the existence of a value) and INSERT or UPDATE (depending on the result of the select) ...
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1answer
371 views

How could I handle heavy load and consistency for product inventory in online retailers? [closed]

I have posted that question on Stackoverflow and they suggest me to repost my question here, as it would more likely to get help from a DB community (regarding this issue). Hope you guys don't mind. ...
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1answer
180 views

Oracle Enterprise Manager - top activity

I'm looking at the Top Activity view in OEM. The left axis is labeled "Active Sessions" (up to 24 in the graph I'm looking at) and there is a line labeled "Maximum CPU". The measured activities ...
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1answer
143 views

PostgreSQL - If I run multiple queries concurrently, under what circumstances would I see a speedup? Under what circumstances would I see a slowdown?

I approach you all humbly as one who is NOT a DBA, and I'm sure that my question is fraught with conceptual shortcomings and "it depends on" land mines. I'm also pretty sure that all of you who ...
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1answer
164 views

What causes lost updates being observed in my SQL Azure database?

I have a SQL Azure database with the following tables: CREATE TABLE [dbo].[UserBalances] ( [UserId] UNIQUEIDENTIFIER UNIQUE NOT NULL DEFAULT NEWID(), [AvailableMoney] INT NOT NULL ...
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1answer
157 views

When and how would MyISAM concurrent insert = always be a problem?

I wish to set concurrent_insert to always on a MyISAM log table, so that inserts wouldn't have to wait for selects to perform when there are some holes in the table. We're talking about 10-20 inserts ...
0
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1answer
310 views

Moving a collection to a new database (v2.2)

To take advantage of the improved concurrency in Mongodb 2.2--namely database level locking--we would like to move a sharded collection to a new database. I have been unable to find any documentation ...
0
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1answer
202 views

Why we use low numbers for concurrent in MySQL benchmarks or HTTP_LOAD? [closed]

I've seen so many times that we use numbers like 5,6 or 10 at most. What is this concurrency? Doesn't it refer to number of simultaneous users in bench? EDIT I'm not talking about any specific ...
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0answers
24 views

How to avoid duplications using a function

I am using this function in a bulk insert to avoid duplication of url paths. CREATE OR REPLACE FUNCTION "univ"."gc_landing"(IN _name text, OUT landing_id int4) RETURNS "int4" AS $BODY$ DECLARE ...
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0answers
15 views

Concurrency Problem in Inserting data

In a PHP-MySQL app we have a memeber table that we use to store our members data. Before inserting a new member we check member existence based on mobile number and if there is any record we update ...
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0answers
42 views

Rowversion column in every table - Bad practice?

I'm currently providing my application with concurrency checks. For that, I'm using Entity Framework combined with SQL Server's RowVersion / Timestamp column. Now I've thought about adding a ...
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1answer
78 views

Concurrent SELECT and UPDATE in multiprocessing python

I have to randomly match about 20 million rows in two tables without using the same row twice using PostgreSQL 9.3.5. Both tables have the following structure CREATE TABLE de_sim_points_end ( -- ...
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1answer
23 views

Running identical queries in sysbench

When benchmarking using sysbench and utilizing concurrency (multiple threads) for example on a table with 1,000,000 records, does sysbench run "identical" queries in a loop on the table?
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40 views

How can I obtain concurrent deletes for this table?

We have a program that is currently doing something to the effect of: SET TRANSACTION ISOLATION LEVEL READ COMMITTED BEGIN TRANSACTION UPDATE [Source].[dbo].[SourceTable] SET [ProcessedOn] = ...
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52 views

Why does the delete/update block each other in this case?

The following drives me crazy. I have: session1>begin; session2>begin; session2>update dummy set salary=1000 where id=11; session1>delete from dummy where id=1; id is the PK ...
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118 views

Handling concurrent updates, inserting if and only if no record already exists

I'm writing a Java application to update a relational database (currently H2, but we'll likely switch to PostgreSQL at some point). I have a process which does the following: Poll an external system ...
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0answers
57 views

MySQL Multiple threads inserting *SAME* record a Bad Thing?

Okay, as I've noted in other questions, I'm not a sophisticated database user even though I took my first course in relational algebra from ted Codd. I've now inherited an application that ...
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0answers
43 views

Oracle User Profile for REST API

What sort of profile would you recommend for an Oracle user that is manifested through a RESTful API; particularly where there will be a lot of asynchronous requests? So we're talking about a ...
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4answers
276 views

Importing data with a lot of SELECTS during transaction

I'm using SQL server 2008 R2 and I have a products table with an auto increment integer id column as primary key and a product_no column (unique) and 6 tables like articles and product_assets which ...
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1answer
39 views

Oracle Concurrent Insertion

We have simple case like Create table t1 (c1 number primary); session1: insert into t1 values (1); //session1 do not commit transaction session2: insert into t1 values (2); Will Session2 ...
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0answers
25 views

Enable sql row versioning and issue in select inserted row

I worked on a project that high rate of insert and select execute on it. after a while I saw below error: was deadlocked on lock resources with another process and has been chosen as the ...