pgsql: Fast ALTER TABLE ADD COLUMN with a non-NULL default - Mailing list pgsql-committers
| From | Andrew Dunstan |
|---|---|
| Subject | pgsql: Fast ALTER TABLE ADD COLUMN with a non-NULL default |
| Date | |
| Msg-id | E1f0zNq-00064z-Sn@gemulon.postgresql.org Whole thread Raw |
| Responses |
Re: pgsql: Fast ALTER TABLE ADD COLUMN with a non-NULL default
|
| List | pgsql-committers |
Fast ALTER TABLE ADD COLUMN with a non-NULL default Currently adding a column to a table with a non-NULL default results in a rewrite of the table. For large tables this can be both expensive and disruptive. This patch removes the need for the rewrite as long as the default value is not volatile. The default expression is evaluated at the time of the ALTER TABLE and the result stored in a new column (attmissingval) in pg_attribute, and a new column (atthasmissing) is set to true. Any existing row when fetched will be supplied with the attmissingval. New rows will have the supplied value or the default and so will never need the attmissingval. Any time the table is rewritten all the atthasmissing and attmissingval settings for the attributes are cleared, as they are no longer needed. The most visible code change from this is in heap_attisnull, which acquires a third TupleDesc argument, allowing it to detect a missing value if there is one. In many cases where it is known that there will not be any (e.g. catalog relations) NULL can be passed for this argument. Andrew Dunstan, heavily modified from an original patch from Serge Rielau. Reviewed by Tom Lane, Andres Freund, Tomas Vondra and David Rowley. Discussion: https://postgr.es/m/31e2e921-7002-4c27-59f5-51f08404c858@2ndQuadrant.com Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/16828d5c0273b4fe5f10f42588005f16b415b2d8 Modified Files -------------- doc/src/sgml/catalogs.sgml | 27 ++ doc/src/sgml/ref/alter_table.sgml | 34 +- src/backend/access/common/heaptuple.c | 629 ++++++++++++++++++++++------ src/backend/access/common/tupdesc.c | 60 +++ src/backend/catalog/aclchk.c | 2 +- src/backend/catalog/heap.c | 171 +++++++- src/backend/catalog/index.c | 4 +- src/backend/commands/cluster.c | 12 +- src/backend/commands/functioncmds.c | 2 +- src/backend/commands/indexcmds.c | 4 +- src/backend/commands/tablecmds.c | 51 ++- src/backend/commands/typecmds.c | 2 +- src/backend/executor/execExprInterp.c | 2 +- src/backend/executor/execMain.c | 13 +- src/backend/executor/execTuples.c | 28 +- src/backend/executor/execUtils.c | 2 + src/backend/optimizer/util/clauses.c | 4 +- src/backend/optimizer/util/plancat.c | 8 +- src/backend/rewrite/rewriteHandler.c | 3 +- src/backend/statistics/extended_stats.c | 2 +- src/backend/utils/adt/ri_triggers.c | 29 +- src/backend/utils/adt/ruleutils.c | 6 +- src/backend/utils/cache/relcache.c | 82 +++- src/backend/utils/fmgr/fmgr.c | 4 +- src/backend/utils/fmgr/funcapi.c | 8 +- src/include/access/htup_details.h | 4 +- src/include/access/tupdesc.h | 3 + src/include/access/tupdesc_details.h | 29 ++ src/include/catalog/heap.h | 6 +- src/include/catalog/pg_attribute.h | 30 +- src/include/catalog/pg_class.h | 2 +- src/test/regress/expected/event_trigger.out | 4 +- src/test/regress/expected/fast_default.out | 515 +++++++++++++++++++++++ src/test/regress/parallel_schedule | 2 +- src/test/regress/serial_schedule | 1 + src/test/regress/sql/fast_default.sql | 357 ++++++++++++++++ 36 files changed, 1898 insertions(+), 244 deletions(-)
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