26
votes
Accepted
MongoDB MMAPv1 vs WiredTiger storage engines
Personally, I prefer the mmapv1 storage engine as of now for three reasons.
Reason 1: Maturity
It isn't that WiredTiger is immature. But mmapv1 is well understood and battle tested all way up and ...
- 3,211
18
votes
Accepted
Do databases make a delete and an insert when having to update rows?
Is this even true?
No, it is an implementation detail. A database may implement a suitable update in place if it so chooses.
What are the benefits?
Splitting an update into a delete followed by an ...
- 82.9k
13
votes
Does AWS RDS support MEMORY storage engine?
This answer applies to AWS Aurora not straight MySQL RDS.
Just because SHOW ENGINES says the database has the MEMORY storage engine doesn't mean you can actually use it. We have found that in AWS ...
- 131
9
votes
Accepted
Understanding IAM Pages: extent intervals
You can see by the red arrow what seems to be 16 pages related to the same extent. How is that possible?
The red arrow points to an entry showing that extents starting at 1:176 and 1:184 are ...
- 82.9k
9
votes
Accepted
What is the stride of a GAM interval
I have available a TB-sized database. There should be plenty of GAM pages to find.
Let's first examine the strides from those documents. 4GB is 524,288 pages. Adding this offset to 2 for the 1st page, ...
- 24.7k
9
votes
What is the stride of a GAM interval
sources
This has been documented in a bunch of places for a long time. The first place I saw it written about was in this blog post from 2012:
Breaking Down TempDB Contention (part 2)
GAM: Page ID = ...
- 38.8k
7
votes
Accepted
Does AWS RDS support MEMORY storage engine?
Yes, it does. How come ? Run this query in the RDS Instance:
mysql> select * from information_schema.engines where engine='MEMORY'\G
*************************** 1. row ***************************
...
- 181k
6
votes
Accepted
MongoDB - Unable to change mongodb storage engine to WiredTiger
Based on the warning message included in your description, you are already using the WiredTiger storage engine but your dbPath is using the ext file system (in theory ext4, but the Linux filesystem ...
- 10.2k
6
votes
Accepted
What page type is page 516855552?
On a newly-created SQL Server 2022 database, the script below shows page 516855552 is a PFS page and 516855553 is a GAM page.
USE master;
DROP DATABASE IF EXISTS GAMTest;
CREATE DATABASE GAMTest
ON ...
5
votes
MongoDB MMAPv1 vs WiredTiger storage engines
My two cents:
Journaling in WiredTiger can lose updates in hard shutdowns because it uses in-memory buffering for storing the journal records.
In between write operations, while the journal ...
- 163
4
votes
Migrate Jira to MySql - Unknown system variable 'storage_engine'
It' already a known Issue in Confluence Docs:
Stop Confluence
Edit <confluence-home>/confluence.cfg.xml
Look for a line similar to:
<property name="hibernate.connection.url">...
- 49
4
votes
MongoDB MMAPv1 vs WiredTiger storage engines
We shifted to WiredTiger from MMAPv1 on the lure of 7x to 10x performance gain. We had to revert back to MMAPv1 as MongoDB would lock up when the WiredTiger cache would hit 100%. We've documented our ...
- 41
4
votes
Accepted
Disable database tables for writes but report writes as successful
MySQL, and friends, i.e. MariaDB and Percona, have a rather unusual storage mechanism called the Black Hole engine - it might help with your particular request (see the fiddle here).
For example, if ...
- 29.5k
4
votes
Kafka Internal Data structure vs LSM tree
No, Kafka does not use LSM trees or any tree based data structure for data representation. It relies upon Sequential IO so that it is not relying upon JVM to maintain cache which would then be ...
- 41
4
votes
What is the stride of a GAM interval
This info can can also be gleaned in newer versions from sys.dm_db_page_info.
Here's a brute-force method on a test database:
SELECT page_info.*
FROM sys.database_files AS df
CROSS APPLY ...
3
votes
howto read/interpret "show engine innodb mutex" output?
(Sorry for the delay; there are some important issues.)
The following things won't explain your mutex questions, but may improve performance such that the questions go away.
Observations:
Version: ...
- 76.9k
3
votes
Accepted
Disabling Aria INSERT log in MariaDB
After lots of experimentations, I found out that the problem was not TRANSACTIONAL, but PAGE_CHECKSUM.
The default behaviour of Aria is PAGE_CHECKSUM=1 for which Aria keeps a copy of the inserting ...
- 4,491
2
votes
Migrate Jira to MySql - Unknown system variable 'storage_engine'
If using Mysql 7 and Jira 7 change the connection string in the mysql.properties file.
sudo vi ${JIRA_APPLICATION_DIR}/atlassian-jira/WEB-INF/classes/database-defaults/mysql.properties
Find the ...
- 176
2
votes
What are reasons **NOT** to use the MEMORY storage engine in MySQL?
The other disadvantage of the MEMORY-based tables is that they can't be referred multiple times in the same query. At least that behaviour was found till the v5.4. How with CTEs (since v8.x) there is ...
- 4,283
2
votes
MySQL lock on MEMORY storage engine, when does it apply?
You said in your question
It makes me think that when you insert/update/replace the table locks itself automatically and entirely so you will not be able to select anything while the write is being ...
- 181k
2
votes
Accepted
DBCC PAGE read page from buffer pool or directly from the file system?
We know that SQL Server always read pages from disk to memory for all its operations.
The pages are asked for from memory like most things in SQL Server. The same process applies for DBCC PAGE as it ...
- 29.9k
2
votes
Accepted
WiredTiger Page Size
The parameter I was looking for is referred to as the allocation_size It's
WiredTiger parameter. From the documentation
A component of WiredTiger called the Block Manager divides the on-disk pages ...
- 183
1
vote
Disabling Aria INSERT log in MariaDB
Many of the system tables in the information_schema, mysql and sys databases use the Aria storage engine, and some of these have transactional=1. So even if you create a table with transactional=0, ...
- 6,251
1
vote
Accepted
How to add sphinx engine to mysql 5.7?
Install MariaDB which will run on top of a MySQL-5.7 data directory. This has SphinxSE included in every mariadb-server package on Ubuntu.
You will need to install the plugin:
INSTALL SONAME '...
- 7,649
1
vote
Accepted
What MariaDB storage engine should i use?
Your only real choice here is between InnoDB and Percona's XtraDB engines - see this page.
Coincidentally, I wrote an answer to Change all table ENGINE at once from "MyISAM" to "InnoDB&...
1
vote
Does any MariaDB engine have the option to declaratively or configuratively abstract highly-redundant data?
In any RDBMS, "normalization" is an explicit task that the programmer does.
Having stuff buried inside JSON strings makes that task more difficult.
- 76.9k
1
vote
Accepted
SQL SERVER Database IO performance impact of splitting database tables into FileGroups and multiple Files per filegroup
Talk with your SAN administrator. That's the source that should be able to explain you with detailed information what kind of SAN you've got and what it is capable of. Have you got MPIO? What's the ...
1
vote
MongoDB - Unable to change mongodb storage engine to WiredTiger
To change Storage Engine in Mongo DB on Ubuntu Linux from WiredTiger to MMAPv1 (or vice versa)
Assuming you don't have data that needs backing up, as you've run into this issue you probably have an ...
- 151
1
vote
Accepted
mongodb inMemory engine available in the community edition?
As at MongoDB 3.4, no plans have been announced to make the In Memory Storage Engine available in the MongoDB Community Edition. I suspect this is likely to remain as an Enterprise-only feature for ...
- 10.2k
1
vote
Accepted
Sync two MySQL servers data, while changing the Engine in the slave
This should not a problem, provided you do not execute any DDL related to the Storage Engine on the Master.
I have written about this many times
Jun 01, 2011 : What can we do in MySQL 5.0 Replication ...
- 181k
Only top scored, non community-wiki answers of a minimum length are eligible