Bucardo/Sequences

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Postgres sequences can be replicated.

Pushdelta syncs and sequences

In most cases, you will not need to replicate sequences, unless your slaves are not read only, or if you want your slaves to be ready for failover. If you do decide to replicate them, just treat them like you would a table - add them to the goat table, gather them into herds, and associate them with one or more syncs.

Swap syncs and sequences

If you are using a swap sync, the best practice is to *not* replicate sequences, but to make sure that they are different on both sides, such that an insert on database A will never conflict with an insert on database B. There are three general ways to do this:

  1. Use interleaving sequences. On database A, define the sequence as START WITH 1 INCREMENT BY 2. On database B, define the sequence as START WITH 2 INCREMENT BY 2. Thus, the two sequences will never have the same value.
  2. Use different ranges. For example, database A would use a sequence of START WITH 1, while database B uses START WITH 100000000. This is not foolproof, as A can eventually catch up with B, although you can define A as MAXVALUE 99999999.
  3. Use a common sequence. This relies on one or both of the databases using a function that makes a call to an external sequence.
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