Tag: covering

Waiting for PostgreSQL 11 – Indexes with INCLUDE columns and their support in B-tree

On 7th of April 2018, Teodor Sigaev committed patch:

Indexes with INCLUDE columns and their support in B-tree
 
This patch introduces INCLUDE clause to index definition.  This clause
specifies a list of columns which will be included as a non-key part in
the index.  The INCLUDE columns exist solely to allow more queries to
benefit from index-only scans.  Also, such columns don't need to have
appropriate operator classes.  Expressions are not supported as INCLUDE
columns since they cannot be used in index-only scans.
 
Index access methods supporting INCLUDE are indicated by amcaninclude flag
in IndexAmRoutine.  For now, only B-tree indexes support INCLUDE clause.
 
In B-tree indexes INCLUDE columns are truncated from pivot index tuples
(tuples located in non-leaf pages and high keys).  Therefore, B-tree indexes
now might have variable number of attributes.  This patch also provides
generic facility to support that: pivot tuples contain number of their
attributes in t_tid.ip_posid.  Free 13th bit of t_info is used for indicating
that.  This facility will simplify further support of index suffix truncation.
The changes of above are backward-compatible, pg_upgrade doesn't need special
handling of B-tree indexes for that.
 
Bump catalog version
 
Author: Anastasia Lubennikova with contribition by Alexander Korotkov and me
Reviewed by: Peter Geoghegan, Tomas Vondra, Antonin Houska, Jeff Janes,
             David Rowley, Alexander Korotkov
Discussion: https://www.postgresql.org/message-id/flat/.4010101@postgrespro.ru

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Waiting for 9.2 – Index only scans

On 8th of October, Tom Lane committed patch:

Support index-only scans using the visibility map to avoid heap fetches.
 
When a btree index contains all columns required by the query, and the
visibility map shows that all tuples on a target heap page are
visible-to-all, we don't need to fetch that heap page.  This patch depends
on the previous patches that made the visibility map reliable.
 
There's a fair amount left to do here, notably trying to figure out a less
chintzy way of estimating the cost of an index-only scan, but the core
functionality seems ready to commit.
 
Robert Haas and Ibrar Ahmed, with some previous work by Heikki Linnakangas.

Continue reading Waiting for 9.2 – Index only scans