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pg_upgrade: improve C comment about what old/new oids match

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This commit is contained in:
Bruce Momjian 2014-03-05 10:43:45 -05:00
parent dd917bb793
commit 65b9671411
1 changed files with 6 additions and 7 deletions
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13
contrib/pg_upgrade/pg_upgrade.c
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@ -15,13 +15,12 @@
* oids are the same between old and new clusters. This is important
* because toast oids are stored as toast pointers in user tables.
*
* FYI, while pg_class.oid and pg_class.relfilenode are initially the same
* in a cluster, but they can diverge due to CLUSTER, REINDEX, or VACUUM
* FULL. The new cluster will have matching pg_class.oid and
* pg_class.relfilenode values and be based on the old oid value. This can
* cause the old and new pg_class.relfilenode values to differ. In summary,
* old and new pg_class.oid and new pg_class.relfilenode will have the
* same value, and old pg_class.relfilenode might differ.
* While pg_class.oid and pg_class.relfilenode are initially the same
* in a cluster, they can diverge due to CLUSTER, REINDEX, or VACUUM
* FULL. In the new cluster, pg_class.oid and pg_class.relfilenode will
* be the same and will match the old pg_class.oid value. Because of
* this, old/new pg_class.relfilenode values will not match if CLUSTER,
* REINDEX, or VACUUM FULL have been performed in the old cluster.
*
* We control all assignments of pg_type.oid because these oids are stored
* in user composite type values.