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Diffstat (limited to 'src/backend/access/heap/README.tuplock')
| -rw-r--r-- | src/backend/access/heap/README.tuplock | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/src/backend/access/heap/README.tuplock b/src/backend/access/heap/README.tuplock index 6441e8baf0e..ddb2defd28b 100644 --- a/src/backend/access/heap/README.tuplock +++ b/src/backend/access/heap/README.tuplock @@ -153,3 +153,14 @@ The following infomask bits are applicable: We currently never set the HEAP_XMAX_COMMITTED when the HEAP_XMAX_IS_MULTI bit is set. + +Reading inplace-updated columns +------------------------------- + +Inplace updates create an exception to the rule that tuple data won't change +under a reader holding a pin. A reader of a heap_fetch() result tuple may +witness a torn read. Current inplace-updated fields are aligned and are no +wider than four bytes, and current readers don't need consistency across +fields. Hence, they get by with just fetching each field once. XXX such a +caller may also read a value that has not reached WAL; see +systable_inplace_update_finish(). |