[jkaczman]

The 1st PR (#1788) introduced support for parsing logical decoding messages from the XLogData payload. The 2nd PR (#1797) added the event triggers that write each DDL statement to the source's WAL as one of those messages.

This 3rd PR extends on that by now actually replaying them. When resharding_replay_ddl = true (off by default), we ask the source for logical messages (by adding "messages" 'true' in START_REPLICATION), and for each one we get from our event trigger, we run the DDL on every destination shard at the same point in the stream inside the transaction being replicated.

Follow up PRs will cover these:

• column added with a default like now() or random() gets different values on the destination
• multi-shard source

[codecov]

Codecov Report

❌ Patch coverage is 93.90863% with 12 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../src/backend/replication/logical/subscriber/ddl.rs	93.22%	8 Missing ⚠️
...c/backend/replication/logical/subscriber/stream.rs	90.24%	4 Missing ⚠️

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