Questions tagged [database-internals]

For technical questions about the internal workings of the database engine.

17 questions with no upvoted or accepted answers
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Constant Scan applying

This question is a continuation of optimizer behavior exploration in regards to VALUES construct started here and here. I want to ask about VALUES and APPLY this time. Using CROSS APPLY to alias an ...
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dm_os_memory_cache_clock_hands understanding

As I mentioned in this question I'm trying to understand the working of clock hands. Simply put clock hands move when there is memory pressure so that cache entries can be removed or the cost can be ...
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1answer
127 views

SQLite Internals - Records

Hey I'm trying to wrap my head around SQLite data storage, specifically how it is storing Records. I've found a book The Definitive guide to SQLlite, where the author explains internal record format (...
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0answers
65 views

How is page data rearranged after clustered index is created?

Can anyone please explain what happens at the page level when clustered indexes are created? How do pages rearrange data once clustered indexes are created?
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My question is in a select statement how do you return the RID along with the table data?

I need your help with a concept I want to show developers, that concept is to help them understand how SQL Server retrieves data from a table. In the event that a developer does not use a clustered ...
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0answers
79 views

Character set issue

Error 'Character set '#255' is not a compiled character set and is not specified in the '/user/share/mysql'. Facing error in replication channel from mysql 8.0.16 to mysql 5.7.25.Is there any ...
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0answers
25 views

DCM page in Filestream_Data_Filegroup

I'm doing some research about the DCM (Differential Change Map) page in SQL Server 2016. This is what I discovered so far: page type: 16 each DCM page covers a GAM interval each data file has a DCM ...
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0answers
707 views

Log file Zeroing

During the creation of the database, I am getting below mentioned information about log file zeroing and I have highlighted my understanding in bold fonts. 2015-08-23 12:42:36.850 spid51 ...
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0answers
181 views

Page Header DB Frag ID Property

I am using SQL Server version: Microsoft SQL Server 2012 - 11.0.2100.60 (X64). I created a single table containing one and only one integer-valued column. I then added one and only one row to the ...
1
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1answer
476 views

SSRS Encryption Key backup location

I would like to know if there is any metadata table/registry entry where we can find the backup location of SSRS Encryption Key. I am working on a power shell report to display the Encryption Key ...
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35 views

B-tree indexing example

I am trying to understand "how" Postgres creates the indexes using b-trees with an example. To be specific, I am looking to understand how the b-tree will look like when the ("Name"...
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188 views

How to delete specific range of data from Service Broker > System Queues data table?

Due to sudden increase of my database .mdf file we found there are 4 internal queue message table are increase unexpectedly. so we decided to delete some range of data from these table. we try this ...
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11 views

BIT VARYING internals

I Have a table called IP_Block in which I created two columns ID of type Bit Varying(32) as PK IP Bloc of type CIDR the construction of the ID is the following : For example for the block 1.0.0.0/8 ...
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347 views

What means execute S_2, S_3 and S_4: COMMIT in Postgresql logs?

I'd noticed different commit types in Postgres log: 2019-12-20 12:00:00 [99999]: [12-1] host=...,user=...,db=... LOG: duration: 1000.000 ms execute S_2: COMMIT 2019-12-20 12:00:00 [99999]: [12-1] ...
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111 views

Trimming copy/delete mysql table rows using Trigger

I am using Freeradius AAA server on Ubuntu 18 server which uses mySQL ver 5.7.27 as DB to store entries. INNODB is being used. It have a table called radacct which stores users accounting /session ...
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132 views

Is there a way to make postgres "COUNT WHERE" query log(N)?

Afaik, now this request SELECT COUNT(*) FROM user WHERE rating > 50 looks like this: find an item with the value of rating 50(or greater) in our b-tree index, pretty fast. Iterate though all items ...
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1answer
87 views

LOAD DATA statement returns a syntax error a fraction of the time

MySQL 5.5.32, MyISAM A LOAD DATA INFILE statement usually executes and returns normally, succeeding at loading the data. On rare occasion it fails, returning a generic syntax error, always indicating ...