One idea I had from this is actually truncating pg_log at some point if
we know all the tuples have the special committed xid. It would prevent
the file from growing without bounds.
Vadim, can you explain how WAL will make pg_log unnecessary someday?
> We've expended a lot of worry and discussion in the past about what
> happens if the OID generator wraps around. However, there is another
> 4-byte counter in the system: the transaction ID (XID) generator.
> While OID wraparound is survivable, if XIDs wrap around then we really
> do have a Ragnarok scenario. The tuple validity checks do ordered
> comparisons on XIDs, and will consider tuples with xmin > current xact
> to be invalid. Result: after wraparound, your whole database would
> instantly vanish from view.
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