注意
聚簇表需要重写表，可能会对业务有影响；聚簇完成后新写入的数据不会再按聚簇的索引排序，对于数据变更频繁的表并不适用。

以下是关于该场景的测试情况：

1. 重新聚簇前SQL执行计划和耗时：

   可以看到聚簇前要扫描的block数为5869（Buffers: shared hit=5869），耗时25ms。

   teledb=# explain (analyze,buffers) select count(1) from t1 where f2=1;"
                                                              QUERY PLAN                        
   ---------------------------------------------------------------------------------------------------------------------------------
    Aggregate  (cost=7208.99..7209.00 rows=1 width=8) (actual time=25.505..25.505 rows=1 loops=1)
      Buffers: shared hit=5869
      ->  Bitmap Heap Scan on t1  (cost=124.87..7185.62 rows=9348 width=0) (actual time=3.567..23.002 rows=10051 loops=1)
            Recheck Cond: (f2 = 1)
            Heap Blocks: exact=5838
            Buffers: shared hit=5869
            ->  Bitmap Index Scan on t1_f2_idx  (cost=0.00..122.53 rows=9348 width=0) (actual time=2.405..2.405 rows=10051 loops=1)
                  Index Cond: (f2 = 1)
                  Buffers: shared hit=31
    Planning time: 0.626 ms
    Execution time: 25.659 ms
   (11 rows)
   

2. 按索引t1_f2_idx重新聚簇：

   teledb=# CLUSTER t1 USING t1_f2_idx; 
   CLUSTER
   

3. 重新聚簇后SQL执行计划和耗时：

   可以看到聚簇后扫描的block数为116（Buffers: shared hit=116），耗时9.9ms。性能提升了2倍以上。

   teledb=# explain (analyze,buffers) select count(1) from t1 where f2=1;
                                                              QUERY PLAN                                            
   ---------------------------------------------------------------------------------------------------------------------------------
    Aggregate  (cost=7201.23..7201.24 rows=1 width=8) (actual time=9.808..9.808 rows=1 loops=1)
      Buffers: shared hit=116
      ->  Bitmap Heap Scan on t1  (cost=124.87..7177.86 rows=9348 width=0) (actual time=1.312..7.348 rows=10051 loops=1)
            Recheck Cond: (f2 = 1)
            Heap Blocks: exact=85
            Buffers: shared hit=116
            ->  Bitmap Index Scan on t1_f2_idx  (cost=0.00..122.53 rows=9348 width=0) (actual time=1.219..1.219 rows=10051 loops=1)
                  Index Cond: (f2 = 1)
                  Buffers: shared hit=31
    Planning time: 0.696 ms
    Execution time: 9.969 ms
   (11 rows)