Function BlockSampler_Init

src/backend/utils/misc/sampling.c:38–55

* BlockSampler_Init -- prepare for random sampling of blocknumbers * * BlockSampler provides algorithm for block level sampling of a relation * as discussed on pgsql-hackers 2004-04-02 (subject "Large DB") * It selects a random sample of samplesize blocks out of * the nblocks blocks in the table. If the table has less than * samplesize blocks, all blocks are selected. * * Since we know the

 * Returns the number of blocks that BlockSampler_Next will return.
 */
BlockNumber
BlockSampler_Init(BlockSampler bs, BlockNumber nblocks, int samplesize,
				  long randseed)
{
	bs->N = nblocks;			/* measured table size */

	/*
	 * If we decide to reduce samplesize for tables that have less or not much
	 * more than samplesize blocks, here is the place to do it.
	 */
	bs->n = samplesize;
	bs->t = 0;					/* blocks scanned so far */
	bs->m = 0;					/* blocks selected so far */

	sampler_random_init_state(randseed, bs->randstate);

	return Min(bs->n, bs->N);
}

bool
BlockSampler_HasMore(BlockSampler bs)