Global sequence management interfaces

Global sequence management interfaces#

PGD provides an interface for converting between a standard PostgreSQL sequence and the PGD global sequence.

The following functions are considered to be DDL , so DDL replication and global locking applies to them.

Sequence functions#

bdr.alter_sequence_set_kind#

Allows the owner of a sequence to set the kind of a sequence. Once set, seqkind is visible only by way of the bdr.sequences view. In all other ways, the sequence appears as a normal sequence.

PGD treats this function as DDL , so DDL replication and global locking applies, if it’s currently active. See Running DDL safely .

Synopsis#

bdr.alter_sequence_set_kind(seqoid regclass, seqkind text, start bigint DEFAULT NULL)

Parameters#

  • seqoid — Name or Oid of the sequence to alter.

  • seqkind — local for a standard PostgreSQL sequence, snowflakeid or galloc for globally unique PGD sequences, or timeshard for legacy globally unique sequence.

  • start — Allows specifying new starting point for galloc and local sequences.

Notes#

When changing the sequence kind to galloc , the first allocated range for that sequence uses the sequence start value as the starting point. When there are existing values that were used by the sequence before it was changed to galloc , we recommend moving the starting point so that the newly generated values don’t conflict with the existing ones using the following command:

ALTER SEQUENCE seq_name START starting_value RESTART

This function uses the same replication mechanism as DDL statements. This means that the replication is affected by the DDL filters

configuration.

The function takes a global DDL lock. It also locks the sequence locally.

This function is transactional. You can roll back the effects with the ROLLBACK of the transaction. The changes are visible to the current transaction.

Only the owner of the sequence can execute the bdr.alter_sequence_set_kind function, unless bdr.backwards_compatibility is set to 30618 or lower.

bdr.extract_timestamp_from_snowflakeid#

This function extracts the timestamp component of the snowflakeid sequence. The return value is of type timestamptz .

Synopsis#

bdr.extract_timestamp_from_snowflakeid(snowflakeid bigint)

Parameters#

  • snowflakeid — Value of a snowflakeid sequence.

Notes#

This function executes only on the local node.

bdr.extract_nodeid_from_snowflakeid#

This function extracts the nodeid component of the snowflakeid sequence.

Synopsis#

bdr.extract_nodeid_from_snowflakeid(snowflakeid bigint)

Parameters#

  • snowflakeid — Value of a snowflakeid sequence.

Notes#

This function executes only on the local node.

bdr.extract_localseqid_from_snowflakeid#

This function extracts the local sequence value component of the snowflakeid sequence.

Synopsis#

bdr.extract_localseqid_from_snowflakeid(snowflakeid bigint)

Parameters#

  • snowflakeid — Value of a snowflakeid sequence.

Notes#

This function executes only on the local node.

bdr.timestamp_to_snowflakeid#

This function converts a timestamp value to a dummy snowflakeid sequence value.

This is useful for doing indexed searches or comparisons of values in the snowflakeid column and for a specific timestamp.

For example, given a table foo with a column id that’s using a snowflakeid sequence, you can get the number of changes since yesterday midnight like this:

SELECT count(1) FROM foo WHERE id > bdr.timestamp_to_snowflakeid(yesterday)

A query formulated this way uses an index scan on the column id .

Synopsis#

bdr.timestamp_to_snowflakeid(ts timestamptz)

Parameters#

  • ts — Timestamp to use for the snowflakeid sequence generation.

Notes#

This function executes only on the local node.

bdr.extract_timestamp_from_timeshard#

This function extracts the timestamp component of the timeshard sequence. The return value is of type timestamptz .

Synopsis#

bdr.extract_timestamp_from_timeshard(timeshard_seq bigint)

Parameters#

  • timeshard_seq — Value of a timeshard sequence.

Notes#

This function executes only on the local node.

bdr.extract_nodeid_from_timeshard#

This function extracts the nodeid component of the timeshard sequence.

Synopsis#

bdr.extract_nodeid_from_timeshard(timeshard_seq bigint)

Parameters#

  • timeshard_seq — Value of a timeshard sequence.

Notes#

This function executes only on the local node.

bdr.extract_localseqid_from_timeshard#

This function extracts the local sequence value component of the timeshard sequence.

Synopsis#

bdr.extract_localseqid_from_timeshard(timeshard_seq bigint)

Parameters#

  • timeshard_seq — Value of a timeshard sequence.

Notes#

This function executes only on the local node.

bdr.timestamp_to_timeshard#

This function converts a timestamp value to a dummy timeshard sequence value.

This is useful for doing indexed searches or comparisons of values in the timeshard column and for a specific timestamp.

For example, given a table foo with a column id that’s using a timeshard sequence, you can get the number of changes since yesterday midnight like this:

SELECT count(1) FROM foo WHERE id > bdr.timestamp_to_timeshard(yesterday)

A query formulated this way uses an index scan on the column id .

Synopsis#

bdr.timestamp_to_timeshard(ts timestamptz)

Parameters#

  • ts — Timestamp to use for the timeshard sequence generation.

Notes#

This function executes only on the local node.

bdr.galloc_chunk_info#

This function retrieves the ranges allocated to a galloc sequence on the local node.

An empty result set will be returned if the sequence has not yet been accessed on the local node.

An ERROR will be raised if the provided sequence name is not a galloc sequence.

Synopsis#

bdr.galloc_chunk_info(seqname regclass)

Parameters#

  • seqname - the name of the galloc sequence to query

Notes#

This function executes only on the local node.

KSUUID v2 functions#

Functions for working with KSUUID v2 data, K-Sortable UUID data. See also KSUUID in the sequences documentation .

bdr.gen_ksuuid_v2#

This function generates a new KSUUID v2 value using the value of timestamp passed as an argument or current system time if NULL is passed. If you want to generate KSUUID automatically using the system time, pass a NULL argument.

The return value is of type UUID.

Synopsis#

bdr.gen_ksuuid_v2(timestamptz)

Notes#

This function executes only on the local node.

bdr.ksuuid_v2_cmp#

This function compares the KSUUID v2 values.

It returns 1 if the first value is newer, -1 if the second value is lower, or zero if they are equal.

Synopsis#

bdr.ksuuid_v2_cmp(uuid, uuid)

Parameters#

  • UUID — KSUUID v2 to compare.

Notes#

This function executes only on the local node.

bdr.extract_timestamp_from_ksuuid_v2#

This function extracts the timestamp component of KSUUID v2. The return value is of type timestamptz .

Synopsis#

bdr.extract_timestamp_from_ksuuid_v2(uuid)

Parameters#

  • UUID — KSUUID v2 value to extract timestamp from.

Notes#

This function executes only on the local node.

KSUUID v1 functions#

Functions for working with KSUUID v1 data, K-Sortable UUID data(v1). Deprecated - See KSUUID in the sequences documentation for details.

bdr.gen_ksuuid#

This function generates a new KSUUID v1 value, using the current system time. The return value is of type UUID.

Synopsis#

bdr.gen_ksuuid()

Notes#

This function executes only on the local node.

bdr.uuid_v1_cmp#

This function compares the KSUUID v1 values.

It returns 1 if the first value is newer, -1 if the second value is lower, or zero if they are equal.

Synopsis#

bdr.uuid_v1_cmp(uuid, uuid)

Notes#

This function executes only on the local node.

Parameters#

  • UUID — KSUUID v1 to compare.

bdr.extract_timestamp_from_ksuuid#

This function extracts the timestamp component of KSUUID v1 or UUIDv1 values. The return value is of type timestamptz .

Synopsis#

bdr.extract_timestamp_from_ksuuid(uuid)

Parameters#

  • UUID — KSUUID v1 value to extract timestamp from.

Notes#

This function executes on the local node.

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