Questions tagged [databases]
The databases tag has no usage guidance.
227
questions
0
votes
2
answers
49
views
Are all NoSQL databases semi-structured?
From Semi-structured data - Wikipedia:
Semi-structured data is a form of structured data that does not obey the tabular structure of data models associated with relational databases or other forms of ...
- 113
0
votes
0
answers
12
views
Query cache management in database servers
Long ago, I remember a bug in which I issued the same database query over and over in a loop. It made me wonder if the server caches the datasets returned by the queries, and how it decides what ...
- 93
0
votes
0
answers
12
views
How can I optimize the performance of a large React application with multiple state updates?
I'm working on a large React application that has several components with frequent state updates. I've noticed that the performance is starting to degrade, especially when there are multiple ...
0
votes
0
answers
14
views
Datastore supporting TTL with range queries
We have a data access pattern in which we need to get users added in the time range say timestamp-1 to timestamp-2 and we don't want to keep older data say max 1 day, so DB should have an inbuilt ...
- 101
0
votes
0
answers
8
views
Can a candidate key for a composite attribute be called a composite key?
Let's take an example of student entity type
Name
Class
Section
Address (Line1, Line2, City, State, Country, PinCode)
Since composite attribute holds multiple atomic attributes, such that the group ...
- 208
0
votes
0
answers
47
views
Sensibility analysis for a discrete output data
I have a dataset with 1055 samples and 168 features. I want to remove some features in order to train a model on my dataset. The model should output a binary field (either 0 or 1 that is known). Some ...
- 101
0
votes
0
answers
12
views
How can I anonymize/ de-identify clinical data present in tabular format
So I have been tasked to anonymize clinical data that..most of the time would be present in the form of tables.
I've looked into algorithms like generalization,redaction,K-anonymity, l-diversity,t-...
- 1
0
votes
0
answers
31
views
How does waiting 7ms and atomic clock help GCP spanner create external consistency?
My understanding why distributed transaction need synchronized clock is the following
Assume NTP max drift is 250ms
...
- 101
0
votes
0
answers
49
views
The Green500 ranks supercomputer energy efficiency. Is there such a ranking of energy efficiency for data centers?
The Green500 is a biannual ranking of the world's most energy-efficient supercomputers. It was first measured in millions of floating-point operations per second per watt of power consumed, and is now ...
- 101
0
votes
0
answers
90
views
Help understand Z order curve range searching
After "speaking" with ChatGPT, I decided to test Z Order Curve.
The code interleaves 2D data, then search for range x: [2..4], y: [2..4]
Programming code using C/C++ should be as follows:
<...
- 105
0
votes
0
answers
20
views
How can Amazon Aurora gain higher read-only throughput?
I read the Amazon Aurora paper and in the performance result section (i.e. 6.1.1), it says
The results are shown in Figure 7 and Figure 6, and measure the
performance in terms of write and read ...
- 101
0
votes
0
answers
38
views
Lock upgradation in Two Phase Locking
Is lock conversion (upgradation) from $Shared$ to $Exclusive$ allowed in
Basic
Conservative
Strict
Rigorous
types of 2PL techniques.
Following is an example of disallowed attempt of lock conversion ...
- 31
0
votes
0
answers
13
views
In SSTables, why is it possible to group records and compress them?
I am currently reading 'Designing Data Intensive Applications' by Kleppman. In the SSTables and LSM Trees section, it is mentioned that one of the advantage of SSTables is:
"Since read requests ...
0
votes
0
answers
17
views
This diagram serves to determine the components of a data entry in my database. What is the name of this type of diagram?
To properly insert a data entry in my database, I have to reach the last box in this diagram. A box represents either a flag or a data structure that participates in determining a single entry. What ...
- 101
0
votes
0
answers
58
views
Is there an algorithm for finding rows that have same sum of column values up to a threshold value?
I have a table like this (more specifically a nested dictionary)
img
a
b
c
d
e
img1
0
0
1
0
1
img2
3
1
0
0
2
img3
4
0
0
0
1
img4
2
2
0
0
0
img5
0
0
0
0
2
img6
2
2
0
0
0
img7
1
0
0
1
0
img8
0
...
- 1
-4
votes
1
answer
68
views
Real world example of complex foregin key references
Give a real world, normalized example where table T1 has primary key (A, B), T2 has primary key (B, C) and T3 has primary key (A, C) and table 4 has a primary key (A, B, C) where (A,B) is a foregin ...
- 75
0
votes
0
answers
97
views
Is there a sorting program or formula to sort and place individuals in classes based on preferences
I am looking for a formula or program to help place people in classes based on their preferences.
The elements of the problem are:
There are 30 class choices a student can pick from.
There are 400 ...
- 1
0
votes
1
answer
85
views
Check whether a decomposition is in 3nf
In a database systems course, we have been presented with the following definition for third normal form (3NF):
A relation $R$ is in 3NF means:
a nontrivial dependency $A_1,\dots,A_n\to B_1,\dots B_m$...
1
vote
0
answers
38
views
Relational calculus: "Find all X with at least y amount of Z"
Assuming I have two relations:
Supplier [ID (PK), Name, City, Country] and
Item [ID (PK), Name, Department, Price, Stock, Supplier_ID (FK)]
What would be the easiest way to determine the following ...
- 11
0
votes
0
answers
25
views
Implement this as Attribute or Entity Set?
I am creating a database on students' interests using the Entity-Relationship Model for a University assignment.
Should I implement the circled stuff as attribute, or an entity set?
2
votes
0
answers
32
views
How can we reduce the spatial complexity of intermediate indexes in relational databases at execution time?
In relational databases, what are the practical or theoretical ways to reduce the size and spatial complexity of intermediate indexes or tables* at execution time (so for example to reduce the size of ...
- 21
0
votes
0
answers
263
views
Algorithm to generate unique suggestions for creating an ID
Let's say I have a service where I provide user registration. The user chooses a ID. Now if I already have someone who is registered against that ID, I will inform the user that this ID is already ...
- 1,034
0
votes
0
answers
23
views
Primary key's all field should contain value or not?
After reading a lot of materials related to the Primary key and Unique key, I am in doubt. Let us consider a primary key (AB) in table R (ABCDE). AB together can not be null as AB is a primary key. ...
- 176
0
votes
0
answers
187
views
Is this decomposition in 3NF?
I have the following question:
Consider relation R(A, B, C, D, E, F, H) with the following functional dependencies:
A --> D, AE --> H, DF --> BC, E --> C, H --> E
Consider three ...
2
votes
0
answers
39
views
Primary File Organization in DBMS - Files of ordered records (sorted files)
"Fundamental of Database Systems", 3rd ed. by Elmasri and Navathe, page 136 says:
"We can physically order the records of a file on disk based on the values of one of their fields [...]&...
- 21
0
votes
0
answers
34
views
Mongodb database model for password manager app
I'm doing a school project where I have to design a password manager app. I was wondering what the data model would look like. I know that I will have the user database to store authentication ...
- 1
0
votes
1
answer
514
views
How are data structures used along databases?
I just completed a Data structures and Algorithms course in my university. I know how data structures work and how different DS are used to solve specific and to improve efficiency. I have also ...
- 35
1
vote
0
answers
40
views
Advantages to create Male and Female entities separate from User rather than making gender a property in a database?
The screenshot is from Georgia Tech's CS-6400. The instructor was talking about inheritance of Sub-Types and Super-Types.
My question is, why are Male and ...
- 11
0
votes
0
answers
92
views
Efficient data structure supporting search query with contains
Suppose I have a table with millions strings in it as keys.
What data structure can I use in order to efficiently support only queries like that?
...
- 101
0
votes
1
answer
19
views
What does it mean to 'provide' an API call?
So I have a database pre-loaded with data related to food recipes and the assignment says:
'Provide an API call that allows us to specify an ingredient or set of ingredients and return full recipes ...
3
votes
1
answer
102
views
Automated Query Equivalence Solver (MongoDB)
The query-equivalence problem is undecidable. However there are theorem provers that attempt to solve instances of undecidable problems. I am curious how I could go about using an automatic theorem ...
- 31
0
votes
1
answer
379
views
AVL Tree rotations
What size is the largest AVL tree for which an insertion could trigger a double rotation?
- 11
0
votes
1
answer
195
views
Figuring out the equivalence between two definitions of "transitive functional dependencies" and intuition behind the intended meaning of definition
The definition given below is present in the exercise of the text Database System Concepts by Korth et. al.
Let $\alpha$ and $\beta$ be sets of attributes such that $\alpha \rightarrow \beta$ holds, ...
- 1,152
1
vote
1
answer
107
views
Is this a mistake in the textbook? Fundamentals of Database Systems 7th ed
Aggregation is an abstraction concept for building composite objects from their
component objects. ... the possibility of combining objects
that are related by a particular relationship instance into ...
0
votes
0
answers
18
views
where to get detailed information about some file format?
i want to learn about the structure of a .blk file but the problem is I don't know where to look for detailed information of this sort, most of the google searches I made gave me links to viewers.
- 1
0
votes
0
answers
370
views
Creating a database of math questions and of answers and a front end for them
Need some guidance on where to begin. I am just learning python if it has any bearing.
I want to create a page on my site where users log in, choose multiple topics from a list, choose between levels ...
- 101
2
votes
1
answer
37
views
How to simplify the query qualification?
Given the following DB and query :
Now if we need to simplify the query qualification, here is the answer from the book (Principle of distributed database systems, third edition) :
My question is in ...
- 23
1
vote
0
answers
26
views
First normal form
I am confused about an aspect of the definition of first normal form in relational database model.
Codd 1970 ("A Relational Model of Data for Large Shared Data Banks") defines normalization (...
- 121
1
vote
0
answers
108
views
constant relation in the base case of relational algebra
in the base case of the inductive definition of the operations of the relational algebra there is also the so called "constant relation" (as for example found in the definition here https://...
- 155
0
votes
0
answers
62
views
What is meant by A determine BC in functional dependency. How the validity of this statement will be checked
We use notation A determines BC in a database for functional dependency. Same way we use equations in mathematics which shows dependency of variables. We have inference rules in logics, functions in ...
0
votes
1
answer
104
views
In database buffering why is it important : no writes to a block (which is to be moved from the disk buffer section of main memory) be in progress?
I was going through the concept of database buffering from the Database System Concepts text by Korth et. al where I came across the excerpt below.
The rules for the output of log records limit the ...
- 1,152
0
votes
1
answer
166
views
WAL rule requires only the undo information in the log have been output to stable storage, and permits the redo information to be written later
I was going through the "write-ahead logging (WAL) rule" from the Database System Concepts text by Korth et. al, where I came across the following excerpt:
Strictly speaking, the WAL rule ...
- 1,152
-1
votes
1
answer
27
views
Is there computer for specify purpose that perform database task?
Is database server really really exist? i mean the server wasn't made by general purpose computer but that database device have their own hardware and architecture.
We know that good database server ...
0
votes
1
answer
61
views
Algorithm to calculate the period where cumulative days within a rolling period exceeds a threshold
I'm struggling to think of the algorithm to transform one data set to another.
The problem I'm looking at is creating a dataset of periods of time where cumulative days absent within a period (eg 30 ...
1
vote
0
answers
38
views
Which of the query approaches are more efficient?
There are two relations, registered(participant,topic) and fee(participant,amount).
The primary key for registered is (participant, topic) and the primary key for fee is participant.
The premise is ...
1
vote
1
answer
188
views
Data model and database schema
I need to test my understanding of the difference between the data model and database schema. According to my understanding, the data model is a description of how the data will be stored and the ...
- 43
2
votes
0
answers
93
views
Database Access Cost Estimate - Linear Search over non-key attribute
How does one estimate the access cost for the below query given that the data is sorted according to a non-key attribute, that the data is not uniformly distributed across all possible values of said ...
- 123
0
votes
1
answer
795
views
What is the difference between a state machine and a database
I didn't study computer science as a degree, so whilst having studied computer science, there are still gaps in my knowledge. Everything I read about 'state' sounds like some form of 'data' but kept ...
- 101
2
votes
2
answers
50
views
If a user confirmed a booking or transaction on the database system, but it failed and it falls over to the replica, what if the transaction is lost?
This is an overall system design and DBMS question:
If the user books a ticket or an item on a website, how do we solve the issue of confirming a ticket is sold to the user, but the main Database ...
0
votes
0
answers
70
views
How attributes helps us to allow column interchange in a relational database?
A relation on two sets $A$ and $B$ is defined as the subset of the cartesian product $$A\times B = \{(a,b),\ a \in A, b \in B\}$$
A database is also a relation and each entry is an ordered tuple ...
- 33