The core for asynchronous programming are the objects Task and Task<T>. Both of them are compatible with the keywords async and await.

First of all we need to identify if the code’s I/O-bound or CPU-bound.

• the code’s limited for external operations and waits for something a lot of time. Examples of this are DDBB calls, or a server’s response. In this case we have to use async/await to free the thread while we wait
• the code does a CPU-intensive operation. Then we move the work to another thread using Task.Run() so we don’t block the main thread.

async code vs parallel code

(!) Asynchronous code is not the same as parallel code (!)

• In async code you are trying to make your threads do as little work as possible. This will keep your app responsibe, capable to serve many requests at once and scale well.
• In parallel code you do the opposite. You use and keep a hold on a thread to do CPU-intensive calculations

async code

The importante of async programming is that you choose when to wait on a task. This way, you can start other tasks concurrently

In async code, one single thread can start the next task concurrently before the previous one completes.
(!) async code doesn’t cause additional threads to be created because an async method doesn’t run on its own thread. (!) It runs on the current synchronization context and uses time on the thread only when the method is active.

parallel code

For parallelism you need multiple threads where each thread executes a task, and all of those tasks are executed at the same time

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Indexes are a basic structure type that apply to one or multiple columns in order to improve performance and speed up queries that: filter, sort or join data for a table.

this may improve performance for a query that uses last_name in a WHERE clause or an ORDER BY

CREATE INDEX idx_last_name ON employees (last_name);

you can also create composite indexes

CREATE INDEX idx_composite ON employees (last_name, first_name)

and also composite index for only active employees

CREATE INDEX idx_active_employees ON employees (status) WHERE status = 'active';

When to use indexes

Frequent filters WHERE - if you usually filter by a specific column (last_name for example), an index should improve performance.

JOIN for big tables - when you use JOIN with big tables through PKs or FKs.

ORDER BY or GROUP BY - queries that search for / group by a specific column also benefit from indexes.

Best practices

Don’t create indexes in every column. This slows things down on insert, delete or update operations.

Index are best used for big domain fields such as ids, names, surnames. Don’t use them for male/female (or boolean) fields.

Keep indexes optimized: operations where you mass update or mass delete items in your tables may fragment your indexes. You may need to periodically check them and REINDEX them.

ALWAYS MEASURE PERFORMANCE TIME before and after the creation of that index. If your index doesn’t improve performance, remove it as it causes overhead.

Reference(s)

https://stackoverflow.com/questions/7744038/decision-when-to-create-index-on-table-column-in-database
https://stackoverflow.com/questions/52444912/how-to-find-out-fragmented-indexes-and-defragment-them-in-postgresql
https://chatgpt.com/

UNION

The union sentence is used to accumulate results for two SELECT sentences.

SELECT column1, column2 FROM table1
UNION
SELECT column1, column2 FROM table2

We have the following tables

company1

company2

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Find an exact match of a nested field (note that .keyword has to be added to string fields)

{
  "query": {
    "bool": {
      "must": [
        {
          "term": {
            "metadata.title.keyword": "File test.pdf"
          }
        }
      ]
    }
  },
  "size": 200
}

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These are my posts with knowledge about Azure services and usage.

Azure CosmosDB
Azure CosmosDB query examples

Azure Cloud Functions
Azure Functions - Introduction

(for this post some formulas and menu names are in spanish as my excel and computer are in spanish and excel formulas depend on this).

The formula is:

=AGREGAR(3;3;J:J)-1

The first two parameters are for the function itself. The important one is J:J which marks the column to count. What’s important here is this is not going to count filtered items in tables.

Watch out with headers! If you have headers in your table, add -1 to your formula.

(for this post some formulas and menu names are in spanish as my excel and computer are in spanish and excel formulas depend on this).

Here is how to find and mark differences in unequal, really long lists or tables in Excel. For my example, one list is a partial list from other. Some items are missing and you’ve to find which ones are.

This is the full list.

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Authentication process of verifying an identity. We confirm they’re who they say they are. (username & pwd).

Authorization process of verifying what someone is allowed to do. (Permissions and access control).

Past solutions

From worst one to best one and the problems they originate:

Credential Sharing

The worst one. An App is not able to differentiate between real user access and programmatical access.
Permissions are typically too broad. It also the ability to access more content than it should.

Cookie

We could redirect the user off to the API where they could enter their credentials and get a cookie. This allows an app to access the API.

Dangerous because CSRF attacks. We’ve authorised the whole browser and not the app.

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How to solve the problem “Low disk space on ‘Filesystem root’. The volume has only xMB disk space remaining” when you completely fill a virtual disk in VirtualBox.

(You have to delete all your snapshots first)

Open a cmd terminal and run the following command:

"c:\Program Files\Oracle\VirtualBox\VBoxManage.exe" modifymedium  
"c:\Users\mario\VirtualBox VMs\Ubuntu OTAN\Ubuntu OTAN.vdi" --resize 30000

The first path is an executable included with VirtualBox.
The second one is where your VDI actually is. --resize takes the size in MBs.

Open gpartitioner and resize it.

JMeter is a testing tool to simulate thousands of users for web testing purposes. It uses Java Threads for this.

1. JMeter
2. JMeter performance testing

Notes on the course “Mobile Design Course - UX, UI and Design Thinking” from Udemy.

Color Theory
Typography
UI Design
UX Design
Mobile Design Workflow

Notes from the course General UI Design

Design ground rules
Design base properties
Design using color and contrast appropiately
Design with typography and imagery
Creating and simplifying visual cues
UI Design Mantras