random generator extension

This PostgreSQL extension implements a couple of functions to generate random values for various data types, which may be useful for testing purposes etc.

Reproducible output

To allow generating repeatable data sets, all functions take a seed and nvalues parameters. The seed determines a subset of possible values to generate, while nvalues determines the number of distinct values.

You can imagine this as as a random number generator initialized with

(seed, k)

where k is one of the nvalues values, picked randomly. The generator is reseeded after every single value. Alternatively, this can be seen as a pair of random number generators PRNG1 and PRNG2, and each function call does this (in pseudocode):

/* get K from global PRNG */
K = generate_value(PRNG1) % nvalues;

/* seed the "local" PRNG with a combination of seed and K */
set_seed(PRNG2, seed + K);

/* generate a value from the "local" PRNG (can be more complex) */
return generate_value(PRNG1);

Note: This does not necessarily mean data sets generated using the same seed will be exactly same. It will contain the same sets of values, but the order of values may be different, the combinations of values inserted into different columns of a table may be different, etc.

Note: The actual number of distinct values generated may be lower than nvalues, due to collisions of the PRNG. The code does not attempt for correct for this.

Functions

random_string(seed, nvalues, min_length, max_length)

Generates a string with the specified length, using ASCII characters, symbols and control characters (newline, carriage return, tabulator).

random_bytea(seed, nvalues, min_length, max_length)

Generates a bytea with the specified length.

random_int(seed, nvalues, min_value, max_value)

Generates a random 32-bit integer in the specified interval.

random_bigint(seed, nvalues, min_value, max_value)

Generates a random 64-bit integer in the specified interval.

random_real(seed, nvalues, min_value, max_value)

Generates a random 32-bit floating point value in the specified interval.

random_double_recision(seed, nvalues, min_value, max_value)

Generates a random 64-bit floating point value in the specified interval.

random_inet(seed, nvalues)

Generates a random INET address. The generated addresses have /32 mask.

random_cnet(seed, nvalues)

Generates a random CNET address. The generated addresses have masks set to 8, 16, 24 or 32, and the addresses are picked with the same probability. This means that addresses with short masks are much less common in the output - for every /8 address we expect 16M /32 addresses.

random_cnet2(seed, nvalues)

Generates a random CNET address. The generated addresses have masks set to 8, 16, 24 or 32, but the addresses don't have the same probability. Instead, data is generates so that each mask length represents the same fraction of the produced values (1/4 for each mask length).

This however means that longer masks will have namy more distinct values, to compensate for this skew (the shorter the mask, the fewer distinct values it can accomodate).

random_macaddr(seed, nvalues)

Generates a random MACADDR value (6B variant).

random_macaddr8(seed, nvalues)

Generates a random MACADDR8 value (8B variant).

License

This software is distributed under the terms of PostgreSQL license. See LICENSE or http://www.opensource.org/licenses/bsd-license.php for more details.