Questions tagged [isolation-level]
For questions about "isolation levels" - the setting that specifies the applicable guarantees of concurrency and consistency in multi-user database systems.
177
questions
1
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2answers
58 views
How are SELECT queries isolated from each other with MariaDB 10.1?
Given the following tables..
CREATE TABLE `event` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`type` varchar(50) COLLATE utf8_general_ci NOT NULL,
`data` longblob NOT NULL,
`...
1
vote
1answer
46 views
What's the correct database behavior when two transactions change the same row/value?
I'm writing a database LRU cache in C++ for an embedded NoSQL database to solve a performance problem, and I'm trying to understand the correct assumed behavior and philosophy behind it.
Say there's a ...
0
votes
0answers
37 views
Deadlock due to serializable isolation level(from my knowledge)
Deadlock occurring on update. Both the updates holding RangeS-S lock and waiting for X lock. Is there any other possible way without changing the isolation level or using the retry logic?
Database ...
3
votes
2answers
502 views
Read-only transaction anomaly
I've learned about this anomaly from these papers: https://www.cs.umb.edu/~poneil/ROAnom.pdf (original) https://johann.schleier-smith.com/blog/2016/01/06/analyzing-a-read-only-transaction-anomaly-...
0
votes
0answers
25 views
Tracking locked rows using dm_tran_locks
I use Azure SQL DB (Basic, DTU, Provisioned). Isolation is default read committed snapshot.
To handle concurrent transactions, I use table hints to lock the row(s). The requirement is that during the ...
1
vote
0answers
93 views
SQL statements to ensure that the same location cannot be reserved more than once on the same day?
I have two tables one for venues (3 locations hall1, hall2 and hall3) and one for orders (a row could be 441,2004,50895,'Requested','2021-01-02 10:53','2021-03-06 11:46',7,3) as follow:
CREATE TABLE ...
4
votes
2answers
273 views
Transaction strategy for UNIQUE constraint?
How to use a transaction-based strategy to ensure that the same location cannot be booked more than once on the same day?
It was suggested to me that it will different for every isolation level. Could ...
1
vote
1answer
67 views
How does PostgreSQL handle parallel transactions with different transaction isolation levels?
I have a typical Java Spring + Postgres environment (the project is legacy). A persistence layer of backend has a mix of declared isolation levels - some of them are the default i.e. READ COMMITED, ...
0
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1answer
27 views
Pessimistic locking and isolation levels
How is pessimistic locking with read and write locks related to isolation levels?
Readers block writers and writers block readers. This behaviour is always constant irrespective of isolation level ...
0
votes
1answer
34 views
Is this atomic set and get in MariaDB / MySQL: `UPDATE t SET col = @my_var := col + 1 WHERE id = 123`?
I want to atomically update a single row and get its value.
I discovered today that MariaDB / MySQL has this additional way of setting user variables using the assignment operator :=, described e.g. ...
0
votes
1answer
31 views
Out-of-order results in the READ UNCOMMITTED isolation level?
On the Wikipedia page for Isolation (database systems), when explaining dirty reads, it says:
The only thing that may be prevented in the READ UNCOMMITTED isolation level is updates appearing out of ...
0
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2answers
67 views
MariaDB event to automatically move data older than a specific time to another table without temporary table?
I am trying to setup an event, that automatically moves data older than a specified amount of time from a heavily used table to some "archive" table to improve performance.
So far I've only ...
1
vote
1answer
159 views
What is isolation level of autocommit?
I'm trying to make sense from "autocommit" concept.
Originally I've heart about it in the context of Java JDBC API Connection.setAutoCommit(boolean autoCommit)
Quick search revealed that the ...
3
votes
2answers
174 views
Blocking on readable secondary replica
We recently migrated from LogShipping standby/read-only setup to Multi Subnet AG setup with readable secondaries.
Generally on old setup we have select queries running for longer duration as the ...
1
vote
1answer
93 views
How to change the default isolation level of a transaction in a stored procedure in PostgreSQL PL/pgSQL?
I am interested in controlling the isolation level of a transaction inside a PostgreSQL procedure but haven't found any information on how to do it. The documentation on Transaction Management within ...
0
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2answers
40 views
Read Committed Shared Lock
I wanted to know when you are at read committed isolation level and in one session someone started an explicit transaction which has a select statement, say it takes 20 seconds. Can someone from a ...
7
votes
1answer
242 views
Missing rows under read committed isolation
It's well known that Read Committed isolation is prone to different anomalies. I read The Great Paul White's series on isolation levels. The post relevant to the discussion is this one:
The Read ...
1
vote
1answer
73 views
RCSI & ETL processing compatibility
The Situation:
I have a write-heavy, read-light ETL workload with the basic process of:
get chunk of raw data (generally 1000-5000 records) from an import landing table.
pass the chunk of data from ...
1
vote
1answer
177 views
Accessing Memory Optimised Tables Under Snapshot Isolation
We have a high traffic database, that I am looking to convert to using IM-OLTP for performance gains.
Due to the large size of the table in question, I'm looking to do a hot/cold solution, with a view ...
3
votes
2answers
58 views
Isolation levels and rows not yet read
Under RR in transaction T1 I do a
SELECT * FROM mytable WHERE city='London'
In another T2 I do
UPDATE mytable SET price=100 WHERE city='London' and id=5000
Is it possible that T2 reads,updates and ...
1
vote
2answers
89 views
Trying to understand an RCSI example-The Potential Dangers of the Read Committed Snapshot Isolation Level
There's this article The Potential Dangers of the Read Committed Snapshot Isolation Level which demonstrates RC vs RCSI isolation levels.
I get the RC example but not the RCSI one.In particular how ...
1
vote
3answers
49 views
How to improve the liveness of a system when having a long-running transaction blocking multiple reading transactions
Is there any recommended approach for improving the application liveness when having, over the same database object, multiple reading transactions, and one long-running transaction which is updating ...
1
vote
2answers
100 views
Dirty read or phantom row
We are having dirty reads or phantom rows in our data warehouse. My question is not how to solve it (it is a long story and I am currently working on it), but I want to know what exactly happens to ...
0
votes
1answer
38 views
Enforcing maximum number of relations for a record
I am trying to figure out the way to enforce a maximum number of relations in a highly concurrent system. The following is an example use case.
// Job table
job_id | ... | num_positions
xx-xx-xx | ....
8
votes
2answers
632 views
UPDATE statement behavior
I have a question regarding inner workings of UPDATE statements with regards to SQL Server. I am trying to understand what will happen if the following 2 update statements are received or serviced at ...
1
vote
2answers
325 views
PostgreSQL sometimes fails to detect serialization failures
I have an http-server in application language that looks roughly like this:
item = SELECT item FROM table WHERE field = 'value'
if (item) {
UPDATE another field on item
} else {
INSERT item VALUE ...
0
votes
1answer
33 views
Transaction isolation level/design for write-only ledger
This is a simplified example of a problem I've been working on. Say I have the following database schema:
Table: Deposits
+--------+------------+--------+---------+
| ID | Date | Amount | ...
2
votes
1answer
430 views
Are SqlServer Sequences, guaranteed to return different values for concurrent transactions?
In documentation it is told that:
Duplicate validation only occurs once a record is fully populated. This can result in some cases where the same number is used for more than one record during ...
0
votes
1answer
98 views
View serializable schedule or not
Could you help me understand why the schedule on the picture is view serializable without any "blind write"?
Also, should the results be the same if two schedules are view equivalent?
I did create ...
1
vote
1answer
545 views
Does ISOLATION LEVEL READ UNCOMMITTED affect Deletes?
I have an exceptional circumstance that made me use SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED. (I am using sp_getapplock to ensure single process access to a given row.)
I am trying my best ...
0
votes
1answer
37 views
dynamic data masking read uncommited
I have read about Dynamic Data Masking and one question is still in my mind. I am wondering what will happen is such scenario:
1. Dynamic Data Masking is set up on table
2. ETL process is loading new ...
0
votes
0answers
35 views
What is correct way to ensure that row is not deleted in concurrent transaction
I have 2 tables:
Parent (PK id)
Child (PK id, parent_id)
Note that parent_id is not defined a foreign key (actually they are not parent/child, I use those names just for example).
I need to handle ...
1
vote
0answers
50 views
Repro for missed rows during Allocation Order Scan + Page Splits
In Read Uncommitted, an index scan can execute as an allocation order scan. If a page split occurs during the scan, it is possible that a row will be read twice if it moves to a later position in the ...
0
votes
1answer
76 views
Do I need to set "ConnectionReset" parameter in the connection string when using isolation levels occasionally?
I have a MySql 5.6.44, and an dotnet application using Mysql.Data 8.0.12.
The application code has not specified any isolation level till now because the default one was enough. Suddenly we need to ...
1
vote
1answer
920 views
What standard SQL isolation levels do the SQLite isolation levels correspond to?
There are four standard SQL isolation levels: Read Uncommitted, Read Committed, Repeated Read, and Serializable. (c.f. Database System Concepts 6ed.)
In SQLite, there are three isolation levels: ...
6
votes
2answers
3k views
Will my SQL query use stale data? How can I prevent it?
I have two tables (SJob & SJobDependent) that I need to join for some logic in a stored procedure. They both have a column (job) that connects them in a one-to-many relationship - one SJob record ...
1
vote
2answers
356 views
Why does START TRANSACTION WITH CONSISTENT SNAPSHOT not work with SERIALIZABLE isolation level?
The MySQL doc for START TRANSACTION says:
The only isolation level that permits a consistent read is REPEATABLE READ. For all other isolation levels, the WITH CONSISTENT SNAPSHOT clause is ignored. ...
-1
votes
1answer
649 views
Serializable Transactions vs SELECT FOR UPDATE in MySQL
I have a stock table with columns: id, available, sold, status fields. Before increasing sold field I have to check if sold + x is less and equal than available. To make sure every transaction uses ...
2
votes
1answer
197 views
How the single SQL statement is isolated?
All the books I've seen so far, talking about transactions show scenarios with several SQL statements involved.
But what's about single statements? What level of isolation do they have? Is it ...
2
votes
0answers
61 views
Choosing between RCSI and Snapshot Isolation [closed]
I have researched into this and I understand the general differences between the two isolation levels. I would like to explain our scenario and need help in deciding the correct isolation level to use....
0
votes
2answers
60 views
Read uncommited does not work in UPDATE WHERE NOT EXISTS
I'm not able to force SQL Server (2016) to respect values updated in the same statement.
What I need to do is to update old values (column a in table #t in demo code below) with mapping table (#u) ...
0
votes
1answer
96 views
Is there an alternative to isolation level SERIALIZABLE?
I use MySQL 5.7 and want to run an export task on a products table. The process basically runs like this:
SELECT * FROM products WHERE exported = 0
Loop over the result set in my programm and write ...
0
votes
1answer
57 views
MSSQL - what is the best isolation level for a website
My website is mostly informative,
Users cannot Update or Delete, they can perform Insert but that almost doesn't happen.
Most of the site uses SELECT queries and the information doesn't change often ...
11
votes
2answers
2k views
Does SQL Server's serializable isolation level lock entire table
Me and a colleague of mine discussed the implications of use of the serializable isolation level. He said it locked the entire table, but I disagreed to that telling him it potentially could but it ...
6
votes
1answer
691 views
Change transaction isolation level inside running transaction
I'm studying transaction isolation levels in SQL Server, and I'm trying to figure out how SQL Server behaves when the isolation level changes during the lifetime of the transaction.
It seems that ...
5
votes
1answer
321 views
SQL Server - How to achieve READCOMMITED and NOLOCK at the same time?
If I have a User table:
id | name | age
1 | Mateus | 27
The first transaction executes an update, and leaves the transaction open, without committing or rolling back:
update User set name = 'John'...
4
votes
1answer
365 views
PostgreSQL Serialisation failure on different ids
Serializable isolation mode can be used to avoid race conditions when upserting equal ids. So for create table u(uid int primary key, name text); if we run two similar transactions T1 and T2:
begin ...
1
vote
1answer
53 views
Difference in location of transaction isolation level declaration - inside/ouside a transaction?
I have been looking though some stored procedured on our system today when I saw the following structure:
(pseudocode indicative of actual SP, server is using the default isolation level):
CREATE ...
0
votes
1answer
435 views
Lock Escalation happening while inserting few million records into a table in production
I want to insert few million records into a table in my production database.
I am not updating any existing rows.I am just doing
INSERT INTO TAB1
SELECT
COL1,COL2,COL3
FROM TAB2
This table has an ...
5
votes
1answer
195 views
NOLOCK or Read Uncommitted locking / latching behaviours
I've read many, many different takes on how NOLOCK or the read uncommitted isolation levels function in terms of locks / latches taken.
When using a SELECT with NOLOCK or in the Read Uncommitted ...
