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base repository: postgresql-cfbot/postgresql
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  • 2 commits
  • 4 files changed
  • 2 contributors

Commits on Aug 9, 2025

  1. no table rewrite when set column type to constrained domain 

    per https://www.postgresql.org/docs/devel/sql-altertable.html
says changing the type of an existing column to a constrained domain
will trigger a table rewrite. However, after reviewing the relevant context [1]
and experimenting with it, I found that it's doable to just a table scan.

the main gotcha is struct NewColumnValue.
we do ``palloc0(sizeof(NewColumnValue));`` in ATExecAddColumn,
ATExecSetExpression, ATPrepAlterColumnType.
ATExecAddColumn:  Adding a new column with domain with constraints will cause
                  table rewrite.
ATExecSetExpression: for stored generated column will cause table rewrite, we do
                     not support domain over virtual generated columns now.
ATPrepAlterColumnType: we only do table rewriting occasionally.see ATColumnChangeRequiresRewrite.

If table rewrite is required, then there is nothing we can do.
we can add a new boolean field, coerce_to_domain, to NewColumnValue. this field
is set to true only when changing an existing column's type to a constrained
domain. In such cases, a table scan is enough—no table rewrite is needed.

[1]: https://www.postgresql.org/message-id/[email protected]
discussion: https://postgr.es/m/XXX
commitfest: https://commitfest.postgresql.org/patch/XXX
    @jianhe-fun
    jianhe-fun authored and Commitfest Bot committed Aug 9, 2025
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  2. [CF 5907] v1 - no table rewrite when set column type to constrained d… 

    …omain

This branch was automatically generated by a robot using patches from an
email thread registered at:

https://commitfest.postgresql.org/patch/5907

The branch will be overwritten each time a new patch version is posted to
the thread, and also periodically to check for bitrot caused by changes
on the master branch.

Patch(es): https://www.postgresql.org/message-id/CACJufxFX0DupbF5+DBNF3mXCFNTZ1Y7jpT11+tCD_FcyADHs2A@mail.gmail.com
Author(s): Jian He
    Commitfest Bot committed Aug 9, 2025
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