Hello, > PostgreSQL can't currently avoid reading the table, because that's > where the tuple visibility information is stored. We've been making > progress toward having some way to avoid reading the table for all > except very recently written tuples, but we're not there yet (in any > production version or in the 9.0 version to be released this > summer). More doubts on how indexes are used by PostgreSQL. It is mentioned that table data blocks have data about tuple visibility and hence table scans are always necessary. So how does PostgreSQL reduce the number of blocks to be read by using indexes? Does this mean that indexes will have references to all the 'possible' blocks which may contain the data one is searching for, and then scans all those blocks and eliminates records which should not be 'visible' to the query being executed? Do index data get updated as and when data is committed and made 'visible' or is it that index data get updated as soon as data is changed, before commit is issued and rollback of transaction results in a rollback of the index data changes too? Regards, Jayadevan DISCLAIMER: "The information in this e-mail and any attachment is intended only for the person to whom it is addressed and may contain confidential and/or privileged material. If you have received this e-mail in error, kindly contact the sender and destroy all copies of the original communication. IBS makes no warranty, express or implied, nor guarantees the accuracy, adequacy or completeness of the information contained in this email or any attachment and is not liable for any errors, defects, omissions, viruses or for resultant loss or damage, if any, direct or indirect." -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
