Alvaro Herrera wrote: > pg_clog is allocated in pages of 8kB apiece(*). On allocation, pages are > zeroed, which is the bit pattern for "transaction in progress". So when > a transaction starts, it only needs to ensure that the pg_clog page that > corresponds to it is allocated, but it need not write anything to it. Of course, in 8.3 it's not when the transaction starts, but when the Xid is assigned (i.e. when the transaction first calls a read-write command). In previous versions it happens when the first snapshot is taken (i.e. normally on the first command of any type, with very few exceptions.) -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc.
