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VACUUM and ANALYZE update the target table's pg_class row in-place, that is nontransactionally. This is OK, more or less, for the statistical columns, which are mostly nontransactional anyhow. It's not so OK for the DDL hint flags (relhasindex etc), which might get changed in response to transactional changes that could still be rolled back. This isn't a problem for VACUUM, since it can't be run inside a transaction block nor in parallel with DDL on the table. However, we allow ANALYZE inside a transaction block, so if the transaction had earlier removed the last index, rule, or trigger from the table, and then we roll back the transaction after ANALYZE, the table would be left in a corrupted state with the hint flags not set though they should be. To fix, suppress the hint-flag updates if we are InTransactionBlock(). This is safe enough because it's always OK to postpone hint maintenance some more; the worst-case consequence is a few extra searches of pg_index et al. There was discussion of instead using a transactional update, but that would change the behavior in ways that are not all desirable: in most scenarios we're better off keeping ANALYZE's statistical values even if the ANALYZE itself rolls back. In any case we probably don't want to change this behavior in back branches. Per bug #11638 from Casey Shobe. This has been broken for a good long time, so back-patch to all supported branches. Tom Lane and Michael Paquier, initial diagnosis by Andres Freund |
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README
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: http://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at http://www.postgresql.org/download/. For more information look at our web site located at http://www.postgresql.org/.