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List:       pgsql-performance
Subject:    [PERFORM] Feature Request: No pg_dump lock on unlogged tables
From:       "McGehee, Robert" <Robert.McGehee () geodecapital ! com>
Date:       2012-03-11 17:38:04
Message-ID: 17B09E7789D3104E8F5EEB0582A8D66FBAA6006CF5 () MSGRTPCCRF2WIN ! DMN1 ! FMR ! COM
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Hello,
Due to a large database size, my weekend database backup (pg_dumpall) takes about 12 \
hours to complete. Additionally, I add the --no-unlogged-table-data option to skip \
any volatile tables. One UNLOGGED table in the database is completely regenerated \
every day with a TRUNCATE TABLE/INSERT command. However, despite the \
--no-unlogged-table-data option, the table still gets locked by the pg_dump(all), \
preventing the operation from completing for several hours during backups.

To the extent possible, I would like to request a way to prevent certain (UNLOGGED) \
tables from being locked against truncate/schema changes for the extent of an entire \
database backup.

For example:
. pg_dump does not lock unlogged tables if --no-unlogged-table-data is set 
. pg_dump supports sequential table locks / unlocks during backups (only the table \
that is currently being copied is locked, rather than all tables for the entire \
                backup).
. Support a way to automatically replace the TRUNCATE command with DELETE if TRUNCATE \
cannot immediately obtain a lock.

Thanks, Robert

Robert McGehee, CFA
Geode Capital Management, LLC
One Post Office Square, 28th Floor | Boston, MA | 02109
Direct: (617)392-8396

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