Speed up ruleutils' name de-duplication code, and fix overlength-name case.

Since commit 11e131854f, ruleutils.c has
attempted to ensure that each RTE in a query or plan tree has a unique
alias name.  However, the code that was added for this could be quite slow,
even as bad as O(N^3) if N identical RTE names must be replaced, as noted
by Jeff Janes.  Improve matters by building a transient hash table within
set_rtable_names.  The hash table in itself reduces the cost of detecting a
duplicate from O(N) to O(1), and we can save another factor of N by storing
the number of de-duplicated names already created for each entry, so that
we don't have to re-try names already created.  This way is probably a bit
slower overall for small range tables, but almost by definition, such cases
should not be a performance problem.

In principle the same problem applies to the column-name-de-duplication
code; but in practice that seems to be less of a problem, first because
N is limited since we don't support extremely wide tables, and second
because duplicate column names within an RTE are fairly rare, so that in
practice the cost is more like O(N^2) not O(N^3).  It would be very much
messier to fix the column-name code, so for now I've left that alone.

An independent problem in the same area was that the de-duplication code
paid no attention to the identifier length limit, and would happily produce
identifiers that were longer than NAMEDATALEN and wouldn't be unique after
truncation to NAMEDATALEN.  This could result in dump/reload failures, or
perhaps even views that silently behaved differently than before.  We can
fix that by shortening the base name as needed.  Fix it for both the
relation and column name cases.

In passing, check for interrupts in set_rtable_names, just in case it's
still slow enough to be an issue.

Back-patch to 9.3 where this code was introduced.

src/test/regress/expected/create_view.out

@@ -1475,6 +1475,33 @@ select * from int8_tbl i where i.* in (values(i.*::int8_tbl));
  4567890123456789 | -4567890123456789
 (5 rows)
 
+-- check unique-ification of overlength names
+create view tt18v as
+  select * from int8_tbl xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxy
+  union all
+  select * from int8_tbl xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz;
+NOTICE:  identifier "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxy" will be truncated to "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+NOTICE:  identifier "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz" will be truncated to "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
+select pg_get_viewdef('tt18v', true);
+                                  pg_get_viewdef                                   
+-----------------------------------------------------------------------------------
+  SELECT xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.q1,      +
+     xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.q2           +
+    FROM int8_tbl xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx +
+ UNION ALL                                                                        +
+  SELECT xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.q1,      +
+     xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.q2           +
+    FROM int8_tbl xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx;
+(1 row)
+
+explain (costs off) select * from tt18v;
+                                         QUERY PLAN                                         
+--------------------------------------------------------------------------------------------
+ Append
+   ->  Seq Scan on int8_tbl xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+   ->  Seq Scan on int8_tbl xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx_1
+(3 rows)
+
 -- clean up all the random objects we made above
 set client_min_messages = warning;
 DROP SCHEMA temp_view_test CASCADE;

src/test/regress/sql/create_view.sql

@@ -487,6 +487,15 @@ select * from tt17v;
 select pg_get_viewdef('tt17v', true);
 select * from int8_tbl i where i.* in (values(i.*::int8_tbl));
 
+-- check unique-ification of overlength names
+
+create view tt18v as
+  select * from int8_tbl xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxy
+  union all
+  select * from int8_tbl xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz;
+select pg_get_viewdef('tt18v', true);
+explain (costs off) select * from tt18v;
+
 -- clean up all the random objects we made above
 set client_min_messages = warning;
 DROP SCHEMA temp_view_test CASCADE;