This would reduce the randomness from 16B to 8B. Would be almost perfectly sequential, but there are two issues with it: For example, we might take a sequence or a timestampĪnd add random data until we have 16B in total. The easiest way to make UUIDs more sequential is to use some sequential Information about the meaning of those parameters. See the next section explaining the design for additional The default values for parameters are selected to work well for a range Uuid_time_nextval(interval_length int default 60, interval_count int default 65536) RETURNS uuid Uuid_sequence_nextval(sequence regclass, block_size int default 65536, block_count int default 65536) The extension provides two functions generating sequential UUIDs using (combined-time GUID) and is more more thoroughly explained in. This idea is pretty much what the UUID wikipedia article calls COMB Randomness too much (which could increase the probability of collisionĪnd predictability of the generated UUIDs). Generating UUIDS in a more sequential pattern, but without reducing the The main goal of the two generators implemented by this extension, is This results in a nicer and cache-friendlier behavior,īut the values are predictable and may easily collide cross machines. The index (new sequence value is larger than all preceding values, sameįor timestamp). Pattern and the new data almost always end up in the right-most part of The index size exceeds shared buffers (or RAM), the cache hit ratioĬompare this to sequences and timestamps, which have a more sequential Indexes - all index leaf pages are equally likely to be hit, forcing This results in poor locality when inserting data into Regular random UUIDs are distributed uniformly over the whole range of Patterns, which helps to reduce random I/O patterns associated with This PostgreSQL extension implements two UUID generators with sequential This idea is not new, and is described as Released By tomasv License BSD Resources The main goal of the two generators implemented by this extension, is generating UUIDS in a more sequential pattern, but without reducing the randomness too much (which could increase the probability of collision and predictability of the generated UUIDs). With small indexes that's fine, but once the index size exceeds shared buffers (or RAM), the cache hit ratio quickly deteriorates. This results in poor locality when inserting data into indexes - all index leaf pages are equally likely to be hit, forcing the whole index into memory. Description Regular random UUIDs are distributed uniformly over the whole range of possible values. Sequential_uuids 1.0.1 This Release sequential_uuids 1.0.1 Date Status Stable Latest Stable sequential_uuids 1.0.2 - Other Releases Abstract UUID generators with sequential patterns, which helps to reduce random I/O patterns associated with regular entirely-random UUID.
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