Warn when distributing unenforceable constraints

[citus-github-bot]

Issue by jasonmp85
Saturday Dec 27, 2014 at 08:15 GMT
Originally opened as citusdata/pg_shard#48

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Certain constraints are unenforceable in a distributed setting: UNIQUE indexes foremost among them. pg_shard will happily propagate a UNIQUE index with nary a peep.

The extension should either warn when propagating these constraints or refuse to distribute tables altogether which contain such constraints.

[ozgune]

@onderkalaci -- did we change this behavior for UPSERT changes? If so, could you document the email thread on this and close this item?

[onderkalaci]

Yes, we had to change the behaviour for UPSERTs.
The new behaviour is as follows:

• Allow unique indexes which include partition column for hash and range partitioned tables.
• Allow unique indexes which include partition column for append partitioned tables with a warning that CitusDB cannot enforce this.
• Do not allow unique indexes/constraints if the constraint does not include the partition column. Without this check, it would be very likely that UPSERTs lead to wrong results.