-This directory contains libpq++, the C++ language interface to POSTGRES95.
+This directory contains libpq++, the C++ language interface to POSTGRESQL.
libpq++ is implemented on of the libpq library. Users would benefit
-from reading the chapter on libpq in the postgres95 users manual
+from reading the chapter on libpq in the PostgreSQL users manual
before using libpq++.
The initial version of this implementation was done by William Wanders
This is only a preliminary attempt at providing something useful for
people who would like to use C++ to build frontend applications to
-postgres95. The API provided herein is subject to change in later
-versions of postgres95.
+PostgreSQL. The API provided herein is subject to change in later
+versions of PostgreSQL.
For details on how to to use libpq++, see the man page in the man/
subdirectory and the test programs in the examples/ subdirectory.
.\" This is -*-nroff-*-
.\" XXX standard disclaimer belongs here....
-.\" $Header: /cvsroot/pgsql/src/man/Attic/cluster.l,v 1.4 1998/01/11 22:17:10 momjian Exp $
+.\" $Header: /cvsroot/pgsql/src/man/Attic/cluster.l,v 1.5 1998/03/14 21:57:56 momjian Exp $
.TH CLUSTER SQL 01/23/93 PostgreSQL PostgreSQL
.SH NAME
cluster - give storage clustering advice to Postgres
.IR classname.
.PP
When a class is clustered, it is physically reordered based on the index
-information. The clustering is static. In other words, if the class is
-updated, it may become unclustered. No attempt is made to keep new
+information. The clustering is static. In other words, as the class is
+updated, the changes are not clusterd. No attempt is made to keep new
instances or updated tuples clustered. If desired, the user can
recluster manually by issuing the command again.
.PP
-The table is actually copied to temporary table in index order,
-then renamed back to the original name. For this reason, all
-grant permissions and other indexes are lost when cluster is performed.
+The table is actually copied to temporary table in index order, then
+renamed back to the original name. For this reason, all grant
+permissions and other indexes are lost when cluster is performed.
+.PP
+In cases where you are accessing single rows randomly within a table,
+the actual order of the data in the heap table unimportant. However, if
+you tend to access some data more than others, and there is an index
+that groups them together, you will benefit from using the CLUSTER
+command.
+.PP
+Another place CLUSTER is good is in cases where you use an index to pull
+out several rows from a table. If you are requesting a range of indexed
+values from a table, or a single indexed value that has multiple rows
+that match, CLUSTER will help because once the index identifies the heap
+page for the first row that matches, all other rows that match are
+probably already on the same heap page, saving disk accesses and speeding up
+the query.
+.PP
+There are two ways to cluster data. The first is with the CLUSTER
+command, which reoreders the original table with the ordering of the
+index you specify. This can be slow on large tables because the rows
+are fetched from the heap in index order, and if the heap table is
+unordered, the entries are on random pages, so there is one disk page
+retrieved for every row moved. PostgreSQL has a cache, but the majority
+of a big table will not fit in the cache.
+.PP
+Another way is to use SELECT ... INTO TABLE temp FROM ... This uses the
+PostgreSQL sorting code, and is much faster for unordered data. You
+then drop the old table, use ALTER TABLE RENAME to rename 'temp' to the
+old name, and recreate the indexes. From then on, CLUSTER should be
+fast because most of the heap data is ordered.
.SH EXAMPLE
.nf
/*
cluster emp_ind on emp
.fi
-
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