skip WAL on COPY patch
От | Steve Singer |
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Тема | skip WAL on COPY patch |
Дата | |
Msg-id | 4E53E7D5.6030808@ca.afilias.info обсуждение исходный текст |
Ответы |
Re: skip WAL on COPY patch
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Список | pgsql-hackers |
The attached patch adds an option to the COPY command to skip writing WAL when the following conditions are all met: 1) The table is empty (zero size on disk) 2) The copy command can obtain an access exclusive lock on the table with out blocking. 3) The WAL isn't needed for replication For example COPY a FROM '/tmp/a.txt' (SKIP_WAL); A non-default option to the copy command is required because the copy will block out any concurrent access to the table which would be undesirable in some cases and is different from the current behaviour. This can safely be done because if the transaction does not commit the empty version of the data files are still available. The COPY command already skips WAL if the table was created in the current transaction. There was a discussion on something similar before[1] but I didn't see any discussion of having it only obtain the lock if it can do so without waiting (nor could I find in the archives what happened to that patch). I'm not attached to the SKIP_WAL vs LOCK as the option 1- see http://archives.postgresql.org/pgsql-patches/2005-12/msg00206.php Steve
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