Where Does My INSERT Go? A Logical Replication Story
summary
Follows one INSERT from executor to subscriber, showing WAL construction, why wal_level=logical adds column and relation metadata, and how ReorderBuffer groups interleaved WAL by XID and LSN to emit ordered changes. Covers WAL sender, logical decoding, replication slots that retain required WAL, output plugins (pgoutput, wal2json/test_decoding) and the apply worker that replays changes and updates confirm_flush_lsn. Notes large transactions can spill reorder buffer to disk and full-page-image writes for crash safety.
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chapters (12)
- 0:00Music & introduction
- 0:41Roadmap: end-to-end replication flow
- 1:53From SQL insert to heap tuple
- 4:00Writing data into shared buffers
- 5:23WAL creation and durability explained
- 7:06Inside a WAL record and crash safety
- 9:02Logical vs physical replication differences
- 11:27WAL sender and logical decoding layer
- 14:07Reordering transactions with reorderbuffer
- 20:14The commit triggers decoding and plugins
- 24:18Applying changes on the subscriber
- 25:11End-to-end journey recap
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