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1
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1answer
34 views

MySQL consistent nonlocking reads vs. INSERT … SELECT

So, from my reading of the MySQL 5.5 documentation and some experiments I did with colleagues, I understand that the following is the case: With InnoDB tables, a simple SELECT statement (one that ...
2
votes
1answer
76 views

Does READ UNCOMMITTED have the same effect as AUTOCOMMIT=1?

AFAIK running transactions as READ UNCOMMITTED means that there is no lock, so every change caused by a transaction is immediately visible to other transactions. Is it correct to assume that this is ...
1
vote
1answer
57 views

Improve performance on concurrent UPDATEs for a timestamp column in Postgres

I am using a timestamp column called updated_at for cache invalidation. More information on this particular technique here. The queries all have the same format UPDATE "managers" SET "updated_at" = ...
0
votes
1answer
29 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 ...
2
votes
2answers
108 views

Way to do MERGE with update source when target not match?

I am trying to write a stored procedure that will take new values from a temp table, merge them into an actual table, giving me the ids of the inserted rows, and the rows that already exist matching ...
1
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0answers
95 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 ...
2
votes
2answers
73 views

Tuning Postgres for Single connection use? Or is postgres wrong tool?

Any rules of thumb for work_mem, maintenance_work_mem, shared_buffer, etc. for a database that DOESN'T anticipate concurrent connections and that is doing lots of aggregate functions? I'm a social ...
0
votes
0answers
44 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 ...
3
votes
1answer
69 views

Can't update trigger because of activity

Trying to add a line to a trigger that is attached to a table that is constantly in use ALTER TRIGGER [dbo].[name_of_trigger] ON [dbo].[name_of_table] AFTER UPDATE BEGIN IF ORIGINAL_LOGIN() in ...
0
votes
2answers
347 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 ...
1
vote
1answer
74 views

How does the transactions interact if you set a different isolation level per connection?

I read that I can have different isolation levels per connection and in the server. The default isolation level is REPEATABLE-READ. So if I have a transaction that issues a SERIALIZED to the client ...
1
vote
2answers
73 views

Transaction basics. What is the result of 2 transactions running concurrently?

I have a rather basic question on transactions. Assume a table Account with a column amount. Now we have the following code: BEGIN $amount = SELECT amount FROM ACCOUNT WHERE id = 123; $amount = ...
0
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0answers
86 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 ...
1
vote
1answer
176 views

DB Locks - How would one handle long transactions and maintain high concurrency?

We're maintaining a POS/WMS Application built in powerbuilder that runs on SQL Server 2008 R2 backend. Recently, we've been having a lot of locking issues and I believe it has to do with how we handle ...
0
votes
0answers
221 views

MySQL Innodb Concurrent Inserts and Selects - can't use multiple threads on FreeBSD

We have an application that needs to be dumping rows into some tables at a much faster rate than it currently is. It is a dual processor xeon DB server with 48gb of ram and a 4 TB disk RAID 10 (for a ...
4
votes
1answer
501 views

How is SQL Server returning both a new value and old value during an UPDATE?

We've had issues, during high concurrency, of queries returning non-sensical results - results the violate the logic of the queries being issued. It took a while to reproduce the issue. I've managed ...
0
votes
1answer
108 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 ...
1
vote
1answer
69 views

How, when and why does implicit changing of transaction isolation level happen?

RCSI (Read Committed Snapshot Isolation) is the setting of a database changing the behavior of (the default) Read Committed isolation level in SQL Server. This is, as I understand, the context of ...
0
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0answers
65 views

MySQL + PHP : avoid dirty read

It's possible to avoid dirty read on a MySql database by using a PHP script? i have three two fields (user, incoming_request , outcoming_request) on my table that keep information (as string) about ...
1
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1answer
49 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 ...
0
votes
1answer
597 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, ...
0
votes
0answers
49 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 ...
0
votes
1answer
108 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 ...
1
vote
1answer
159 views

How to insert and or update a variable number of records and prevent concurrency issues

I currently have the following stored procedure. However I am seeing some race conditions where I end up with incorrect data which I think is caused because the procedure isn't attomic and it can be ...
1
vote
0answers
112 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 ...
2
votes
1answer
688 views

oracle blocking sessions

I am trying to investigate some concurrency issues on Oracle 11 RAC. So far the most helpful tool I have is "blocking sessions" view of the Enterprise Manager, which tells me which query is blocking ...
0
votes
1answer
874 views

Putting a Select statement in a transaction

What is the difference between these 2 queries: start transaction; select * From orders Where id=1; UPDATE orders SET username="John" Where id=1; commit; And without transaction: select * From ...
0
votes
1answer
184 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 ...
5
votes
2answers
122 views

Inconsistency in repeatable read

http://www.postgresql.org/docs/9.2/static/transaction-iso.html The Repeatable Read mode provides a rigorous guarantee that each transaction sees a completely stable view of the database. However, ...
6
votes
1answer
879 views

LATCH_EX Waits on Resource METADATA_SEQUENCE_GENERATOR

We have a process that generates an inventory report. On the client side, the process splits of a configurable number of worker threads to build a chunk of data for the report that corresponds to one ...
3
votes
1answer
904 views

PostgreSQL concurrent increment of counter

I need to maintain a statistical table for a project, composed by a list of items and their usage (Think about something like a website in which you would like to count pageviews). Each time an item ...
2
votes
1answer
137 views

Read-only on an SQLite database which is being modified by another program

I wrote a program that has an SQLite database, modifying it every few seconds. Now I want to write a small gadget program that would just read a bit of info from that database (read-only) and display ...
2
votes
1answer
640 views

unique constraint violated (ORA-00001) in concurrent insert [closed]

I have a procedure that is called from concurrent transactions: //Some actions here INSERT INTO table1 (table1_id, table1_val1, table1_val2, table1_val3) VALUES ...
2
votes
0answers
79 views

How to safely take an SQL job out of the schedule?

There is a table | jobID | status | startTime | endTime | and a job, that is scheduled to run every X seconds, it will take the first undone job ID, put it in stored proc and run it. Stored proc takes ...
5
votes
1answer
792 views

How to improve performance on PostgreSQL when using multiple concurrent processes?

Seeing query performance which is not satisfactory on our Python application, which runs several processes that use SQLAlchemy core to access a PostgreSQL 9.2 database. We may have around 100 - 200 ...
-1
votes
4answers
206 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 ...
2
votes
1answer
312 views

Isolation and atomiticy of SQL Server UPDATE

Is there any difference in atomicity and isolation between the two following SQL statements? Batch A: UPDATE Orders SET InProgress = 1 WHERE Completed = 0 and Batch B: UPDATE Orders SET ...
1
vote
1answer
1k 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. ...
0
votes
2answers
392 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) ...
0
votes
0answers
40 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 ...
11
votes
4answers
3k views

Locking issue with concurrent DELETE / INSERT in PostgreSQL

This is pretty simple, but I'm baffled by what PG does (v9.0). We start with a simple table: CREATE TABLE test (id INT PRIMARY KEY); and a few rows: INSERT INTO TEST VALUES (1); INSERT INTO TEST ...
1
vote
1answer
942 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 ...
0
votes
1answer
231 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 ...
4
votes
1answer
481 views

How large should my pool size be? And should I use pgbouncer?

I have a Rails application with 4 Unicorn workers. How do I determine what postgresql database pool size I should use? And if I have 6 applications connecting to this postgres database, would that be ...
4
votes
2answers
727 views

SQL Server (2012) non-blocking DDL?

I'm not very experienced with SQL Server, so maybe I'm missing something My situation is as follows: Session 1 runs a CREATE TABLE (or other CREATE statements) with autocommit off and the CREATE is ...
2
votes
1answer
659 views

performance issues when concurrent requests

We are using SQL Server 2008 R2 on a Windows Server 2008 server. We have some main functions which uses some Stored Procedures which has a lot of sub-queries inside of it. I'll take one SP as an ...
1
vote
1answer
161 views

timestamp based concurrency

I am wondering if someone could help me out with a question I have about time stamp based concurrency. I found the following practice problem on a website It basically asks which of the following ...
0
votes
1answer
199 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 ...
1
vote
1answer
474 views

Which Optimistic Concurrency Control method will work out best in the long run?

These are the options I've thought of: DotNet Dave: UPDATE mytable set f1=newval where id=666 and f1 := f1ValueFromSelect Charlie Checksum: UPDATE mytable set f1=newval where id=666 and ...
3
votes
1answer
1k views

Concurrency with Select-conditional Insert/Update/Delete - PostgreSQL

I have an intervals table which stores a start date and an end date for variables variable_id (four columns : id, start, end, variable_id). Clients compute new intervals for one variable and store ...