On 7th of April 2023, Tom Lane committed patch:
Add array_sample() and array_shuffle() functions. These are useful in Monte Carlo applications. Martin Kalcher, reviewed/adjusted by Daniel Gustafsson and myself Discussion: https://postgr.es/m/9d160a44-7675-51e8-60cf-6d64b76db831@aboutsource.net
Continue reading Waiting for PostgreSQL 16 – Add array_sample() and array_shuffle() functions.
On 9th of January 2023, Tom Lane committed patch:
Invent random_normal() to provide normally-distributed random numbers. There is already a version of this in contrib/tablefunc, but it seems sufficiently widely useful to justify having it in core. Paul Ramsey Discussion: https://postgr.es/m/CACowWR0DqHAvOKUCNxTrASFkWsDLqKMd6WiXvVvaWg4pV1BMnQ@mail.gmail.com
Whenever I'm doing some testing I need sample data. Easiest way to do it is to generate data using some random/generate_series queries.
But what if I need specific frequencies?
For example, I need to generate 10,000,000 rows, where there will be 10% of ‘a', 20% of ‘b', and the rest will be split equally between ‘c' and ‘d'?
On 3rd of April 2019, Alvaro Herrera committed patch:
Log all statements from a sample of transactions This is useful to obtain a view of the different transaction types in an application, regardless of the durations of the statements each runs. Author: Adrien Nayrat
Continue reading Waiting for PostgreSQL 12 – Log all statements from a sample of transactions
Couple of people asked, on irc, about how to generate unique, short, ids for rows.
Since I wrote code for this for explain.depesz.com, I figured that instead of pointing to sources, and letting everyone to extract the functions, I will, instead, write a set of functions that what is needed in reusable way.
On 15th of May, Simon Riggs committed patch:
TABLESAMPLE, SQL Standard and extensible Add a TABLESAMPLE clause to SELECT statements that allows user to specify random BERNOULLI sampling or block level SYSTEM sampling. Implementation allows for extensible sampling functions to be written, using a standard API. Basic version follows SQLStandard exactly. Usable concrete use cases for the sampling API follow in later commits. Petr Jelinek Reviewed by Michael Paquier and Simon Riggs
Continue reading Waiting for 9.5 – TABLESAMPLE, SQL Standard and extensible
In previous posts in this series, I talked about how to read EXPLAIN output, and what each line (operation/node) means.
Now, in the final post, I will try to explain how it happens that Pg chooses “Operation X" over “Operation Y".