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When (1) autovacuum = off and (2) there's at least one database with an XID age greater than autovacuum_freeze_max_age and (3) all tables in that database that need vacuuming are already being processed by a worker and (4) the autovacuum launcher is started, a kind of infinite loop occurs. The launcher starts a worker and immediately exits. The worker, finding no worker to do, immediately starts the launcher, supposedly so that the next database can be processed. But because datfrozenxid for that database hasn't been advanced yet, the new worker gets put right back into the same database as the old one, where it once again starts the launcher and exits. High-speed ping pong ensues. There are several possible ways to break the cycle; this seems like the safest one. Amit Khandekar (code) and Robert Haas (comments), reviewed by Álvaro Herrera. Discussion: http://postgr.es/m/CAJ3gD9eWejf72HKquKSzax0r+epS=nAbQKNnykkMA0E8c+rMDg@mail.gmail.com
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/.