Doc: Tweak description of B-Tree duplicate tuples.
Defining duplicates as "close by" to each other was unclear.  Simplify
the definition.
Backpatch: 13-, where deduplication was introduced (by commit 0d861bbb)
@@ -635,10 +635,10 @@ options(<replaceable>relopts</replaceable> <type>local_relopts *</type>) returns
A duplicate is a leaf page tuple (a tuple that points to a table
row) where <emphasis>all</emphasis> indexed key columns have values
that match corresponding column values from at least one other leaf
- page tuple that's close by in the same index. Duplicate tuples are
- quite common in practice. B-Tree indexes can use a special,
- space-efficient representation for duplicates when an optional
- technique is enabled: <firstterm>deduplication</firstterm>.
+ page tuple in the same index. Duplicate tuples are quite common in
+ practice. B-Tree indexes can use a special, space-efficient
+ representation for duplicates when an optional technique is
+ enabled: <firstterm>deduplication</firstterm>.
</para>
<para>
Deduplication works by periodically merging groups of duplicate
