til/postgres/set-a-seed-for-the-random-number-generator.md

Set A Seed For The Random Number Generator

In PostgreSQL, the internal seed for the random number generator is a run-time configuration parameter. This seed parameter can be set to a particular seed in order to get some determinism from functions that utilize the random number generator. The seed needs to be something between 0 and 1.

We can see this in action by setting the seed and then invoking random() a couple times. Doing this twice, we will see the reproducibility we can achieve with a seed.

> set seed to 0.1234;
SET

> select random();
      random
-------------------
 0.397731185890734

> select random();
      random
------------------
 0.39575699577108
(1 row)

> set seed to 0.1234;
SET

> select random();
      random
-------------------
 0.397731185890734

> select random();
      random
------------------
 0.39575699577108

The seed can also be configured with the setseed() function.

See the PostgreSQL docs for more details.