doc PG 18 relnotes: Add incompatibility note about checksums now default

Reviewed-by: Tomas Vondra 
Discussion: https://www.postgresql.org/message-id/flat/CAKAnmmKwiMHik5AHmBEdf5vqzbOBbcwEPHo4-PioWeAbzwcTOQ%40mail.gmail.com

diff --git a/doc/src/sgml/release-18.sgml b/doc/src/sgml/release-18.sgml
index d7340465e7925d0cddd4ba5fd3d4897701b7c07f..19e770c65b5dc5ac96a047669bfe956a9036f759 100644 (file)
--- a/doc/src/sgml/release-18.sgml
+++ b/doc/src/sgml/release-18.sgml
@@ -192,6 +192,27 @@ Change pg_backend_memory_contexts.level and pg_log_backend_memory_contexts() to
 
 These were previously zero-based.
 
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+initdb defaults to enabling data checksums
+§
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+The previous default behavior (checksums disabled) can be obtained using the
+new option --no-data-checksums.  Note that pg_upgrade will reject upgrading
+between clusters with different checksum settings, so if the old cluster does
+not have checksums enabled (the previous default), then the new cluster will
+need to be initialized with --no-data-checksums in order to allow pg_upgrade
+to succeed.
+