decoder_raw, Output plugin for logical replication
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This output plugin for logical replication generates raw queries based
on the logical changes it finds. Those queries can be consumed as they
are by any remote source.

UPDATE and DELETE queries are generated for relations using a level of
REPLICA IDENTITY sufficient to ensure that tuple selectivity is guaranteed:
- FULL, all the old tuple values are decoded from WAL all the time so
they are used for WHERE clause generation.
- DEFAULT, when relation has an index usable for selectivity like a
primary key.
- USING INDEX, because the UNIQUE index on NOT NULL values ensures
that tuples are uniquely identified.
In those cases, for DEFAULT and USING INDEX, WHERE clause is generated
with new tuple values if no columns mused by the selectivity index are
updated as server does not need to provide old tuple values. If at least
one column is updated, new tuple values are added, of course only on the
columns managing tuple selectivity.
Based on that, UPDATE and DELETE queries are not generated for the following
cases of REPLICA IDENTITY:
- NOTHING
- DEFAULT without a selectivity index

INSERT queries are generated for all relations everytime using the new
tuple values fetched from WAL.

Options
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The following options can be used:
- include_transaction, 'on' will print BEGIN and COMMIT messages, while
'off' bypasses them and generates nothing.
- output_format, 'textual' for textual format, or 'binary' for binary
format. Default is 'textual'.

This worker is compatible with PostgreSQL 9.4 and newer versions.

TODO
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- Implement options filtering INSERT generation depending on REPLICA
IDENTITY level of relation involved.