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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drop postgres table with minimal locking

I'm trying to run the following Postgres migration script DROP TABLE some_table; DROP TABLE another_table; The problem is that this script causes excessive locking when run on the production ...
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4answers
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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 ...
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1answer
1k views

SQL Server 2008, database completely locked

Our database becomes completely locked, and it seems that many tables not related to each other are locked at once. When this happens, it becomes locked for approximately 2 minutes, and when this ...
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2answers
421 views

Schema blocking in READ_COMMITTED_SNAPSHOT

I am trying to troubleshoot locking behavior and the READ_COMMITTED_SNAPSHOT isolation level while attempting to resolve concurrency issues. Background: Assume an online ordering system (ecommerce). ...
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2answers
3k views

Parallel inserts cause deadlock on DB2

The scenario is the following: The application attempts to insert into the same table from two parallel threads making 4000 insertions in each thread (separate transaction per thread). It causes the ...
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3answers
2k views

How can I ensure that only one copy of a procedure is running in Oracle?

We have the need to ensure that only one copy of a particular procedure is running in Oracle. If it is already running and a user tries to open another, then it should error. Whats the best method ...
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3answers
1k views

Does SSRS lock the table when querying?

My senior DBA told me that SQL Query execution by default doesn't lock the table. I was having some issues with my SQL Server Reporting Services (SSRS) report which seems to be getting some issues ...
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1answer
830 views

Can operations in a loop cause table locks?

I know a bit about locking etc, that when a transaction is working on a table, if it is altering a certain amount of data it might try and lock the entire table (I'm sure that is over simplified, but ...
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0answers
101 views

Being careful about additional records being added in a duplicate record merge?

We have a multi-user MS-Access 2003 database. Connecting to it using SQuirrel SQL, and the JDBC/ODBC bridge, I've managed to eek transactions of some sort out of JET by turning off autocommit. I've ...
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1answer
3k views

How do I swap tables in MySQL?

Suppose, I have a table foo, which contains some statistics that are computed every now and then. It is heavily used by other queries. That's why I want to compute more recent statistics in foo_new ...
3
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1answer
351 views

SQL Server : KEY lock prevents FK on nearby row, but not SELECT [closed]

I have the following table structure (simplified, pseudocode): TABLE dbo.Users (Id int NOT NULL IDENTITY PRIMARY KEY) TABLE dbo.Transfers ( Id int NOT NULL IDENTITY PRIMARY KEY, ...
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2answers
181 views

DELETE LOW_PRIORITY row visibility

I have a large MyISAM table on MySQL 5.5(Windows XP x64) on which I will have to run DELETE LOW_PRIORITY queries. Does DELETE LOW_PRIORITY make the rows invisible to SELECT statements immediately and ...
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2answers
334 views

Writing transactions to .MYD file to take Backup

I'm trying to backup MySQL DB by archiving the data directory of required databases. I'm doing FLUSH TABLES WITH READ LOCK before taking the backup, but even then some of the transactions were not ...
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2answers
21k views

way to prevent queries from waiting for table level lock

We've encountered a problem after moving the database of our customer to an extra server. This should have had positive effects on the site's performance, but there is a problem with table locking in ...
3
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3answers
2k views

Cannot write to mysql database while select query in process

Running Mysql 5.1.57 on InnoDB, and have a database locking issue. I have two separate sessions connected to a single database MySQL. On the first session, I run a long SELECT query (technically a ...
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2answers
5k views

FIFO queue table for multiple workers in SQL Server

I was attempting to answer the following stackoverflow question: What SQL Server 2005/2008 locking approach should I use to process individual table rows in multiple server application instances? ...
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1answer
158 views

Optimising a query using hint locks

I have a stored procedure that is being called very frequently. For some database servers it is as often as 20 times per second. Unfortunately because different clients call this procedure, I can't ...
3
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1answer
268 views

All-or-none exclusive lock on 2 SQL tables

My simplistic testing suggested that I can acquire an exclusive lock on 2 tables or postpone acquiring the lock on either until both can be acquired at once by using a query like this: SELECT ...
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1answer
1k views

Lock wait timeout exceeded on insert despite low lock_time in the slow query log

Our Java/Spring application reports occasional lock wait timeouts on single record INSERTs to a MySQL 5.5 InnoDB table. Here are a few slow query log records for some of the failed INSERTs. # ...
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2answers
869 views

enq: TX - row lock contention creating session waits

The database I'm working on has session waits due to DMLs on numerous tables in a procedure. The DBA identifies this as enq: TX - row lock contention. How can I resolve this issue?
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1answer
672 views

Locking order in cursors (Oracle)

I wonder if the order in which records are locked is guaranteed when I use SELECT ... FOR UPDATE in cursors ? For example, DECLARE CURSOR test_cursor IS SELECT field1, field2 FROM table1 ORDER ...
5
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1answer
5k views

MySQL get next unique value without auto increment

I have an MySQL database (InnoDB) that I'm developing for tracking Work Orders at my organization. There are multiple 'sites', and each site has work order numbers starting at 100. WorkorderID ...
2
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1answer
992 views

In InnoDB, does a Transaction imply any implicit locking of a table?

The Isolation level is REPEATABLE_READ. The logic is as under: Transaction begins Read data from Table A If (Table A has Any Data) End Transaction and exit If Table A has No Data, Proceed further ...
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1answer
373 views

JDBC Read uncommitted in SQL Server

If I set the jdbc isolation level to read uncommitted in SQL Server, will SQL Server ever lock any tables, pages, rows etc? Thanks.
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2answers
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how does SQL Server know to lock view objects?

Not sure whether this is a more or less appropriate place to ask this question, originally posed at Stack Overflow. In SQL Server 2008 I have a view V over tables A and B that looks roughly like ...
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1answer
2k views

What factors contribute to lock-percentage with MongoDB

We're attempting to better optimize how we're using our MongoDB instance. We seem to be routinely getting high lock-percentages, and are looking to help minimize that. Here is some mongostat output: ...
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2answers
1k views

Will an ALTER TABLE ADD COLUMN on a slave break replication?

I need to add a last_modified column to a MyISAM table tbl_items. The crux of this problem is that tbl_items houses several gigabytes of data. Also of note, I am using a master-slave deployment with ...
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INSERT statements in a transaction and locking a range of rows

I have a table that is concurrently accessed by many users. Typically, INSERTs to the table are made one at a time. Occassionaly, users will add a "batch" of rows at the same time. The batch is ...
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2answers
201 views

Web application using SQL Server 2008 starts hanging

We have a custom web application that uses SQL Server 2008 (10.50.1600). It's worked fine for years, but lately web pages that return data "instantaneously" have begun showing the "endless swirly blue ...
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2answers
2k views

MySQL Locks while CREATE TABLE AS SELECT

I am running the following (dummy) query CREATE TABLE large_temp_table AS SELECT a.*, b.*, c.* FROM a LEFT JOIN b ON a.foo = b.foo LEFT JOIN c ON a.bar = c.bar Suppose the query ...
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4answers
5k views

Can I be automatically notified of prolonged blocking in SQL server?

About once a week I have to resolve a blocking chain on a SQL Server 2005 database, caused by a long-lived read lock from an Access 2003 front-end. The lock is taken out whenever a user opens a ...
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1answer
547 views

oracle - does this have the potential to cause a lock?

Note how no commit was done in between each statement. Could this cause a table lock or blocked session? delete from tableblah; insert into tableblah (select * from othertable);
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2answers
2k views

How to lock a Row while I'm using it

I want to be able to Lock a row, select it, increment its value, and then release the lock. (without lockin the other rows, so that other connections can work with the rest of the table) I've found ...
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1answer
4k views

How can I find who holds the lock based on the hex-dumped?

I've been reading the Diagnosing MySQL InnoDB Locks article. Karl E. Jørgensen writes on 2008 so I'm consfusing it is in effect. I would like to supply a snippet of the SHOW ENGINE INNODB STATUS: ...
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1answer
2k views

Why can't I get a lock on an InnoDB table?

I have problem with lock table command: LOCK TABLE v3_cam_date WRITE; the command always running with state: "Waiting for table metadata lock". Try to find out which thread was hold the lock on ...
2
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1answer
360 views

Jet OLEDB driver refuses to open a linked table where the original has a lock - any way to force this?

I have a requirement to read reference data from several access databases for an ETL job. The data owners have produced a file with a series of linked tables that consolidates them all into one ...
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1answer
830 views

MySQL hang in load data infile command

From the link: LOAD DATA (400k rows) INFILE takes about 7 minutes, cannot kill the "logging slow query" process? I had changed the command order (unlock before commit + replace some ...
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2answers
244 views

Summary of locks for a query

Does SQL Server have any simple way to fetch metrics on how many (and possibly what type) of locks a given query has taken out during the course of it's execution? Rationale... I'm in the process of ...
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4answers
510 views

Resources for understanding SQL Server locking and concurrency?

As demonstrated by a recent question of mine locking and concurrency are HARD. Can you suggest any good resources for intermediate-to-advanced SQL professionals to do a thorough study on these that ...
18
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3answers
4k views

Managing concurrency when using SELECT-UPDATE pattern

Let's say you have the following code (please ignore that it's awful): BEGIN TRAN; DECLARE @id int SELECT @id = id + 1 FROM TableA; UPDATE TableA SET id = @id; --TableA must have only one row, ...
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1answer
265 views

Checking lock granularity

I understand in SQL Server there are various levels of granularity for locks...RID, Key, Page, Extent, Table, DB. Forgetting about lock escalation, I just want to check the default level of lock ...
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1answer
227 views

Oracle block usage

I am wondering about a weird deadlock and after checking all other components I am considering it to be a INITRANS problem in Oracle 11.2. Now three questions arose: Is there some way of analyzing ...
3
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2answers
3k views

LOAD DATA (400k rows) INFILE takes about 7 minutes, cannot kill the “logging slow query” process?

MySQL version: 5.5.13 The query that I'm using: SET AUTOCOMMIT=0; LOAD DATA INFILE '/data10/select_into.outfile/v3_zone_date.out' INTO TABLE v3_zone_date FIELDS TERMINATED BY ','; COMMIT; ...
2
votes
2answers
841 views

How do I determine what object two SQL process are contending over?

When long running Query#1 exclusively locks an object (table, index or page), and then Query#2 is executed by another user and becomes blocked on the lock held by Query:1, how would I get the name of ...
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1answer
65 views

Reading and writing the common data

I have a couple tables and application service that intensively inserts, updates its. From the other hand some client application have to read data using those tables. Sometimes client application ...
3
votes
1answer
652 views

mysqladmin debug writes out Current locks but PROCESSLIST and INNODB STATUS don't show any

I'm using the 1.1.8 mysql-cacti-templates to gather metrics on MySQL 5.0.77 (CentOS 5.7). Both the InnoDB Current Lock Waits and InnoDB Lock Structures graphs are charting with Cur[rent] values but ...
2
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2answers
2k views

SET LOCK_TIMEOUT, is it session or statement based?

For what period does the LOCK_TIMEOUT LAST? I do a "SET LOCK_TIMEOUT 10" and a "SELECT @@LOCK_TIMEOUT" in one command after a login and get 10 returned. Immediately after this I do a "SELECT ...
5
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2answers
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SQL Server Transaction Timeout

Is there a way in SQL Server 2008 R2 to cause a timeout for a database modification involving a transaction? We have a scenario where our application code hangs or throws an exception and fails to ...
25
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4answers
2k views

Is NOLOCK always bad?

I am a Report Developer who wants to make my queries as efficient as possible. I used to work with a DBA who told me - I believe because I was always dealing with reports on a Production Server - to ...
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2answers
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What are the disadvantage/consequences of moving updated column to separate table to prevent table lock on the original table?

I have a table p with a column points. There are a couple of million of records in the table and i need to regularly calculate and update the points for each row. This process takes a couple of ...