On Fri, Mar 17, 2023 at 12:20 AM Bharath Rupireddy <bharath.rupireddyforpostg...@gmail.com> wrote: > +1 for pg_get_wal_block_info emitting per-record WAL info too along > with block info, attached v2 patch does that. IMO, usability wins the > race here.
I think that this direction makes a lot of sense. Under this scheme, we still have pg_get_wal_records_info(), which is more or less an SQL interface to the information that pg_waldump presents by default. That's important when the record view of things is of primary importance. But now you also have a "block oriented" view of WAL presented by pg_get_wal_block_info(), which is useful when particular blocks are of primary interest. I think that I'll probably end up using both, while primarily using pg_get_wal_block_info() for more advanced analysis that focuses on what happened to particular blocks over time. It makes sense to present pg_get_wal_block_info() immediately after pg_get_wal_records_info() in the documentation under this scheme, since they're closely related. It would make sense to explain the relationship directly: pg_get_wal_block_info() doesn't have the block_ref column because it breaks that same information out by block instead, occasionally showing multiple rows for particular record types (which is what its "extra" columns describe). And, pg_get_wal_block_info() won't show anything for those records whose block_ref column is null according to pg_get_wal_records_info(), such as commit records. (Checks pg_walinspect once more...) Actually, I now see that block_ref won't be NULL for those records that have no block references at all -- it just outputs an empty string. But wouldn't it be better if it actually output NULL? Better for its own sake, but also better because doing so enables describing the relationship between the two functions with reference to block_ref. It seems particularly helpful to me to be able to say that pg_get_wal_block_info() doesn't show anything for precisely those WAL records whose block_ref is NULL according to pg_get_wal_records_info(). -- Peter Geoghegan