Re: First draft of PG 19 release notes

Hi Bruce,

While looking for bugs in new 19 features, I found some changes that
look intended, but I think the notes do not tell an upgrading user about
them. I checked the notes as of 58d16be8acd and ran each one on 19 and
18.6.

1. io_workers was removed (d1c01b79d4a). The item lists the new
variables but not that the old one is gone. An 18 postgresql.conf that
sets it stops 19 from starting.

2. The Snowball item (7dc95cc3b94) names only Dutch, but English and
German stems changed too. "biologist" now stems to "biolog" and
"arbeitet" to "arbeit". A tsvector stored by 18 for "biologist" no
longer matches a 19 query for the same word. Jeff asked about this in
[1].

3. With lz4 as the default (34dfca29343), some long text keys that fit
in a btree with pglz no longer fit. Restoring an 18 dump fails at ADD
PRIMARY KEY with "index row size 3344 exceeds btree version 4 maximum
2704", and the table is left without its key. Setting
default_toast_compression to pglz avoids it.

4. The hash join change (1811f1af98f) can write outer rows with NULL
keys to a temp file, even with one batch. A LEFT JOIN with 297000 NULL
keys wrote 33 MB of temp files, 18.6 wrote none. With temp_file_limit at
1MB it fails.

5. The wait event item gives only the type rename. The event BufferPin
is now BufferCleanup (6c5c393b740), and LWLock BufferContent became the
Buffer events BufferShared, BufferShareExclusive and BufferExclusive
(fcb9c977aa5). The old names are gone from pg_wait_events.

6. The checkpoint log line now carries the request flags (5b93a5987bd).

18.6: checkpoint complete: wrote 3783 buffers
19: checkpoint complete: fast force wait: wrote 6659 buffers

The 18 notes had a sentence when this line changed, maybe 19 needs one
too.

7. LSNs are now zero padded (2633dae2e48), in pg_lsn output and
pg_controldata.

18.6: 0/31CFA58
19: 0/031CFA58

So '0/31CFA58'::pg_lsn::text = '0/31CFA58' is now false.

8. DETACH PARTITION CONCURRENTLY no longer adds a CHECK constraint to
the detached table (3231fd04552). There is no item, and alter_table.sgml
still says it does. I can send a patch for that sentence.

[1]
https://postgr.es/m/0da578e3c70dcfd92d2fdd33f4bac549b3f97bca.camel@j-davis.com

Thanks,
Shihao