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While reviewing Tomas' extended statistics patch I noticed that the new
docbook toolchain produces additional links for each indexterm, based on
the <secondary> tags there are.  For instance, in 9.5 I see this:

statistics, Aggregate Functions, The Statistics Collector
    of the planner, Statistics Used by the Planner, Updating Planner Statistics
https://www.postgresql.org/docs/9.5/static/bookindex.html#AEN186176

while in 10 I see this for the same source:

statistics, Aggregate Functions, Statistics Used by the Planner, Updating Planner Statistics, The Statistics Collector
    of the planner, Statistics Used by the Planner, Updating Planner Statistics
https://www.postgresql.org/docs/devel/static/bookindex.html#indexdiv-S

Note that the links for entries on the <secondary>of the planner</> also
show up in the first list of links.

Is this intended?  As we get more <secondary> entries, this gets busy
real quick, for no gain that I can see.  For instance, I added this
entry:

  <indexterm zone="extended-statistics">
   <primary>statistics</primary>
   <secondary>of the planner</secondary>
   <tertiary>extended</tertiary>
  </indexterm>

and this results in:

statistics, Aggregate Functions, Statistics Used by the Planner, Updating Planner Statistics, The Statistics Collector,
ExtendedStatistics 
    of the planner, Statistics Used by the Planner, Updating Planner Statistics, Extended Statistics
        extended, Extended Statistics

which seems altogether excessive.  Perhaps this is a bug in the index
generation?


FWIW I'm leaning towards removing the <tertiary> in the new entry, which
results in this:

statistics, Aggregate Functions, Statistics Used by the Planner, Updating Planner Statistics, The Statistics Collector,
ExtendedStatistics 
    of the planner, Statistics Used by the Planner, Updating Planner Statistics, Extended Statistics

I think this would be better:

statistics, Aggregate Functions, The Statistics Collector
    of the planner, Statistics Used by the Planner, Updating Planner Statistics, Extended Statistics

--
Álvaro Herrera                         Developer, https://www.PostgreSQL.org/
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