A mechanism for managing concurrent access to shared data or resources by granting temporarily exclusive access to the processes requesting the lock.

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5
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1answer
656 views

How to disable or delete an index

I created a non-clustered index on a live server (SQL Server 2008 R2) and it turned out not to give the performance benefits that I was hoping for. So I want to delete the index again. Unfortunately ...
2
votes
1answer
443 views

Does MySQL guarantee atomic upgrade from read lock to write lock?

If a client session is currently holding a read lock (to allow concurrent reads while already preventing writes), and then acquires a write lock on the same table(s), does MySQL guarantee that the ...
10
votes
1answer
8k views

Deadlock when update different rows with non-clustered index

I'm solving a deadlocking issue while I noticed the lock behavior is different when I use clustered and non-clustered index on the id field. The deadlock issue seems to be solved if clusted index or ...
0
votes
2answers
246 views

When do I need transactions /locks?

I know that transactions are meant to group several operations as one. But if for example in the same table one transaction does DELETE FROM table where state = 'done' and another does either SELECT ...
0
votes
0answers
100 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 ...
4
votes
2answers
1k views

Is there a rule of thumb regarding the size and number of a buffer pool instances?

I know the consensus seems to be approximately 75% of ram should be dedicated to the buffer pool. But, I'm more interested in the optimal number of buffer pool instances. What are some things to ...
0
votes
1answer
606 views

mysql - Waiting for table level lock on a table

I have a problem with my website.. The last few days, at random times the website has become very slow. I started to investigate the best I could. I saw that the MySQL process was using 85 - 95% of ...
1
vote
1answer
739 views

When tables are locked does MySQL queue queries?

I have a small production website, but it's live 24/7. When running the Optimize, Analyze or Repair commands, MySQL locks the table it is working on. QUESTIONS How would this effect users trying ...
1
vote
1answer
6k views

How to query-and-increase a value (counter) in a thread-safe way? (avoid race conditions)

In a table where each row has a counter (just an integer value), I need to get the current value and increase it at the same time. Effectively, I want to do this: SELECT counter FROM table WHERE id=...
0
votes
1answer
1k views

Reporting Services TempDB lock blocking report generation

Two days ago one of our reports in Reporting Services started to take much longer to generate. Its generation time had increased from 4 seconds to 2 minutes. Investigation found: The Stored ...
4
votes
1answer
2k views

SQL Server 2008 R2: query RECENT locks, NOT current locks

The database had average lock wait time of 30 seconds for a period of about a minute. I didn't run my lock query in time to see what was happening. I can't seem to find anything that shows recent ...
15
votes
2answers
681 views

Lock CREATE TABLE

In another application I was struck by bad design: multiple threads execute an EnsureDatabaseSchemaExists() method concurrently, which looks basically like this: IF NOT EXISTS (SELECT * FROM sys....
2
votes
0answers
1k views

SQL Server - Same query, same database, different results [closed]

I have a database in SQL Server 2008 with 2 tables. I'm running the following query on Management Studio: select M.FD_BROWSER_SHORT_NAME AS X, Count(1) AS Y from TB_EVENTS E INNER JOIN ...
4
votes
0answers
325 views

User locking tables without privileges [closed]

This is a restatement of a question asked on the GIS Stack Exchange here. Although it has GIS-specific elements it may be be a more general PostgreSQL effect. I have a PostgreSQL 8.4.4 database ...
1
vote
2answers
530 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 ...
1
vote
1answer
882 views

Can I alter a view being referenced with schemabinding if the change fulfills the binding requirement?

In SQL Server 2008, I have views WITH SCHEMABINDING and I need to alter one. I am changing a column while not changing its alias so consumers will be unaffected. If I were to drop all my other views ...
1
vote
2answers
1k views

MySQL views and table locking (5.1 MyISAM)

I have a large (160 million rows, 50GB) table in MySQL 5.1 using MyISAM. If I were to construct a view defined by a fairly complicated query, would a SELECT on the view lock the underlying table?
1
vote
1answer
493 views

Lock time not involved in MySQL slow query selection?

I wish to analyze some read-write contentions problems on a very huge table where writes are very fast, less than 1ms in most case. The point is that the contention makes those write queries sometimes ...
6
votes
1answer
2k 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 ...
14
votes
5answers
501 views

What is the exact relationship between a database transaction and locking?

This is a humble question asked in the spirit of increasing my knowledge; kindly be gentle in your response. As a long-time application developer, I know at some level what a transaction is (I use ...
2
votes
0answers
971 views

How to make SSAS Commit Write take less time

We're using SQL Server Analysis Server 2012 (Enterprise) and have a process to update the cube during the day. This process is running pretty well until it gets to the final part of processing where ...
8
votes
2answers
8k views

In SQL Server, how do read locks work?

Suppose I have the following long-running query UPDATE [Table1] SET [Col1] = 'some value' WHERE [Col2] -- some clause which selects thousands of rows and suppose the following query is executed ...
8
votes
1answer
8k views

When changing the size of a nvarchar column, do I need to drop the unique index? And will the table get locked when recreating the index?

In our database a big table exists that more or less looks like this: CREATE TABLE dbo.production_data ( pd_id BIGINT PRIMARY KEY, serial NVARCHAR(16) NOT NULL UNIQUE, ... ); but now ...
2
votes
1answer
330 views

What is happening with locks in my database?

I'm having some problems on my database. At any given time, I'm trying to execute an update with five records on my table, but this table is locked and I get a time out executing the query. I ...
2
votes
4answers
134k views

How to determine if an Oracle table is locked or not?

We've been using BI software and a repository database that are installed on Oracle Enterprise 11gR2. Some of these batch reports will try to access a database table which may still be locked. How ...
0
votes
0answers
2k views

Oracle Transaction recovery: lock conflict caught and ignored

In alert log there are a lot of "Transaction recovery: lock conflict caught and ignored" statements. I've found some information, that this error is caused when there is an active dead transaction. ...
2
votes
1answer
374 views

How to use proper hints for Upsert involving a top 1 subquery

For this specific case (tracking Load Balancer switches) we wish to optimize an Upsert so that it does not exhibit any race conditions, cause any PK violation, or acquire any over sized locks. ...
2
votes
2answers
640 views

Reducing deadlocks with update query hint or other method

I'm getting 20-30 deadlocks per day on the same table. (2 mil rows) Profiler DeadlockGraphs show KEY LOCK and PAGE LOCK (See attched jpg) Total datatype size per row = 114 bytes We have multiple ...
1
vote
1answer
152 views

Locks in SQL Server - Update/Select

I am new to SQL Server and am not sure about how the locking mechanism works here. Please help Issue: Need to delete close to 5 mil records in a table. A website pulls data from that table quite ...
1
vote
1answer
139 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 ...
2
votes
1answer
473 views

Can I limit the time a table lock is being held server side?

I have a SQL Azure server with some stored procedures with TABLOCKX hints that I call from C# code on a Windows Azure web role VM. I'm kinda paranoid about those hints - what if there's some network ...
1
vote
1answer
1k views

Can we set LOCK_TIMEOUT instance- or database-wide?

It is possible to change the SQL Server's default (which is -1 or indefinite period of time) LOCK_TIMEOUT value session-wide. Is it possible to set LOCK_TIMEOUT default value server-, instance- and/...
0
votes
2answers
236 views

Should we explicitly lock MyISAM tables or is it implicit…?

Does MyISAM tables automatically lock a table for each select or insert statement .... I mean if I query the database as select * from tablename then does the MySQL engine first lock it for read ...
0
votes
0answers
102 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
3answers
4k views

How can I find who has allocated a user lock via dbms_lock?

We have a print queue process that acquires a user lock via dbms_lock.allocate_unique. It performs the work and then releases the lock. The process works very well. Today, we have a process that ...
2
votes
1answer
1k views

mysql “Lock wait timeout exceeded” two transaction with different keys indexed

I have set of tables that I need to delete their records with a specific key and insert new records. Different transactions are used one for each key: Transaction 1: DELETE FROM table1 WHERE id=1; --...
0
votes
1answer
441 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
votes
2answers
5k views

How to unlock a table in IBM DB2 Data Studio 3.1?

I know the process to unlock a table through IBM DB2 Control Center using activity monitor, but I am completely new to IBM DB2 Data Studio 3.1 Administrative Tool. Whenever i am right clicking on that ...
1
vote
1answer
5k views

Row locking within stored procedure [duplicate]

I have a SQL Server Stored Procedure for getting the next number in sequence stored in a configuration table: declare @val as int SELECT @val = LongValue from tblSystem WHERE [Key] = @Key; SET @val =...
1
vote
1answer
1k views

How does locking work in INSERT..ON DUPLICATE KEY UPDATE statements?

I am encountering deadlocks while trying to update multiple rows (a batch) using INSERT..ON DUPLICATE KEY UPDATE. Does MySQL lock all the rows in one batch or does it lock only the row it is updating ...
0
votes
1answer
4k views

mysql is locked; can't kill query

I have a mediawiki running on my local machine and just started running mysqldump last night: $ mysqldump -h localhost -u wikiuser --default-character-set=UTF8 wikidb --add-locks --skip-lock-table&...
0
votes
0answers
181 views

Lock timeouts on a table with two keys, where only one connection writes for a given value of the first key at a time

I have a table user_rollup_message_list that is keyed by (user_id, message_reference). It is a write-heavy table, and gets enough writes that I get many lock timeouts, with a timeout of 50 seconds, ...
0
votes
2answers
145 views

Does ROLLBACK TRAN honor LOCK_TIMEOUT value?

I have a following stored procedure on my system. BEGIN TRY BEGIN TRAN SET LOCK_TIMEOUT 10000 UPDATE tbl COMMIT TRAN END TRY BEGIN CATCH IF @@TRANCOUNT > 0 ROLLBACK TRAN END CATCH ...
3
votes
1answer
2k views

MySQL: Alter Table on very active table gives “Waiting for table metadata lock”

At my work, we've recently upgraded to MySQL 5.5 and since then, have been bitten a few times by the new (and intended) behavior of metadata locking. Basically, whenever we run an ALTER TABLE ...
1
vote
0answers
954 views

Unable to insert into or update table

A have the following table in a SQL Server 2000 database (service pack 2), with about 600,000 rows: Id [int, primary key] Form [int] Element [int] Data [char(8000)] MoreData [varchar(8000)] ...
2
votes
3answers
241 views

In what order does postgresql handle queries which have conflicting locks?

Let's say that I have a long running query SELECT and this query holds a AccessShareLock on a table. While this query is being processed a new query which needs a AccessExclusiveLock on the table ...
1
vote
1answer
2k views

PostgreSQL transaction locked database table: “idle in transaction”

I have a web application interacting with PostgreSQL (v8.4 & Centos Linux) which suddenly started locking some of the database's tables. Still have no idea what happened, since the code is not new,...
1
vote
2answers
2k views

How to avoid locks by large transactions?

We have a large application running, that requires cleanup for performance reasons. This was however not forseen when designing the application. Basically, the delete is executed from a stored ...
4
votes
1answer
25k views

What is causing Waiting for table level lock errors?

We got the database hanging twice already and trying to find a cause. show processlist Waiting for global read lock | INSERT INTO {myisam_table} ... In here the disk space was full so we thought ...
1
vote
1answer
284 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 ...