Handle VM and FSM truncation WAL records in the page server.

Fixes issue #190.

Original patch by Konstantin Knizhnik.

test_runner/zenith_regress/expected/zenith-rel-truncate.out

@@ -17,3 +17,29 @@ SELECT * FROM truncatetest;
 (0 rows)
 
 DROP TABLE truncatetest;
+--
+-- Test that the FSM is truncated along with the table.
+--
+-- Create a test table and delete and vacuum away most of the rows.
+-- This leaves the FSM full of pages with plenty of space
+create table tt(i int);
+insert into tt select g from generate_series(1, 100000) g;
+delete from tt where i%100 != 0 and i > 10000;
+vacuum freeze tt;
+-- Delete the rest of the rows, and vacuum again. This truncates the
+-- heap to 0 blocks, and should also truncate the FSM.
+delete from tt;
+vacuum tt;
+-- This can be used to look at the FSM directly, if the 'pg_freespace' contrib module
+-- is installed
+--SELECT blkno, avail from generate_series(1, 450) blkno, pg_freespace('tt'::regclass, blkno) AS avail;
+-- Insert a row again. It should go on block #0. If the FSM was not truncated,
+-- the insertion would find a higher-numbered block in the FSM and use that instead.
+insert into tt values (0);
+select ctid, * from tt;
+ ctid  | i 
+-------+---
+ (0,1) | 0
+(1 row)
+
+drop table tt;

test_runner/zenith_regress/sql/zenith-rel-truncate.sql

@@ -16,3 +16,31 @@ VACUUM truncatetest;
 SELECT * FROM truncatetest;
 
 DROP TABLE truncatetest;
+
+
+--
+-- Test that the FSM is truncated along with the table.
+--
+
+-- Create a test table and delete and vacuum away most of the rows.
+-- This leaves the FSM full of pages with plenty of space
+create table tt(i int);
+insert into tt select g from generate_series(1, 100000) g;
+delete from tt where i%100 != 0 and i > 10000;
+vacuum freeze tt;
+
+-- Delete the rest of the rows, and vacuum again. This truncates the
+-- heap to 0 blocks, and should also truncate the FSM.
+delete from tt;
+vacuum tt;
+
+-- This can be used to look at the FSM directly, if the 'pg_freespace' contrib module
+-- is installed
+--SELECT blkno, avail from generate_series(1, 450) blkno, pg_freespace('tt'::regclass, blkno) AS avail;
+
+-- Insert a row again. It should go on block #0. If the FSM was not truncated,
+-- the insertion would find a higher-numbered block in the FSM and use that instead.
+insert into tt values (0);
+select ctid, * from tt;
+
+drop table tt;