11/22/2023 0 Comments Postgresql non sequential primary keyThe unique_rowid() function creates a unique integer composed of the current time at a 10-microsecond granularity and the instance-id. This behavior is statistically likely to be globally unique except in extreme cases (see this FAQ entry for more details). This function produces a 64-bit integer (i.e., INT8) from the current timestamp and ID of the node executing the INSERT or UPSERT operation. However, in both cases the unique_rowid() function is ultimately used to generate new values. The difference between rowid and virtual_sequence is that the latter setting also creates a virtual (pseudo) sequence in the database. In both modes rowid and virtual_sequence, a value is automatically generated using the unique_rowid() function. Generated values for modes rowid and virtual_sequence This allows you to set a default value for all users for any session variable that applies during login, making the sql.defaults.* cluster settings redundant. Use ALTER ROLE ALL SET instead of the sql.defaults.* cluster settings. These modes can be configured with the session variable serial_normalization. When this mode is set, the _sequences_cache_size cluster setting controls the number of values to cache in a user's session, with a default of 256. When the cache is empty, the underlying sequence will only be incremented once to populate the cache. The real data type depends on SERIAL variant. SERIAL creates a regular SQL sequence and implies DEFAULT nextval(), caching the results for reuse in the current session. SERIAL creates a regular SQL sequence and implies DEFAULT nextval(). The real data type is always INT8, regardless of the default_int_size session variable or _int_size cluster setting. SERIAL creates a virtual sequence and implies DEFAULT nextval(). SERIAL implies DEFAULT unordered_unique_rowid(). There are five possible translation modes for SERIAL: Mode These are not guaranteed to increase monotonically, see this section below for details. The chosen DEFAULT expression ensures that different values are automatically generated for the column during row insertion. The result of this translation is then used internally by CockroachDB, and can be observed using SHOW CREATE. The keyword SERIAL is recognized in CREATE TABLE and is automatically translated to a real data type and a DEFAULT expression during table creation. UUIDs ensure more effectively that multiple nodes share the insert load when a UUID column is used in an index or primary key. In most cases, we recommend using the UUID data type with the gen_random_uuid() function as the default value, which generates 128-bit values (larger than SERIAL's maximum of 64 bits) and more uniformly scatters them across all of a table's underlying key-value ranges. New applications should use real data types and a suitable DEFAULT expression. SERIAL is provided only for compatibility with PostgreSQL.
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