diff options
Diffstat (limited to 'src/backend/commands/cluster.c')
| -rw-r--r-- | src/backend/commands/cluster.c | 11 |
1 files changed, 7 insertions, 4 deletions
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c index 997449ef29e..9408f259a61 100644 --- a/src/backend/commands/cluster.c +++ b/src/backend/commands/cluster.c @@ -787,16 +787,19 @@ copy_heap_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex, * When doing swap by content, any toast pointers written into NewHeap * must use the old toast table's OID, because that's where the toast * data will eventually be found. Set this up by setting rd_toastoid. - * This also tells tuptoaster.c to preserve the toast value OIDs, - * which we want so as not to invalidate toast pointers in system - * catalog caches. + * This also tells toast_save_datum() to preserve the toast value + * OIDs, which we want so as not to invalidate toast pointers in + * system catalog caches, and to avoid making multiple copies of a + * single toast value. * * Note that we must hold NewHeap open until we are done writing data, * since the relcache will not guarantee to remember this setting once * the relation is closed. Also, this technique depends on the fact * that no one will try to read from the NewHeap until after we've * finished writing it and swapping the rels --- otherwise they could - * follow the toast pointers to the wrong place. + * follow the toast pointers to the wrong place. (It would actually + * work for values copied over from the old toast table, but not for + * any values that we toast which were previously not toasted.) */ NewHeap->rd_toastoid = OldHeap->rd_rel->reltoastrelid; } |