DB2：

DB2有个reorgchk的命令，是从SYSSTAT.TABLES和syscat.indexes这两个系统表中查表和索引的信息，并给出是否需要reorg表和索引的建议。

[db2inst1@t3-ucm-ucm-rdb ~]$ db2 reorgchk CURRENT STATISTICS on table DB2ADMIN.ACAGENTTREE

Table statistics:

F1: 100 * OVERFLOW / CARD < 5
F2: 100 * (Effective Space Utilization of Data Pages) > 70
F3: 100 * (Required Pages / Total Pages) > 80

SCHEMA.NAME                     CARD     OV     NP     FP ACTBLK    TSIZE  F1  F2  F3 REORG
----------------------------------------------------------------------------------------
Table: DB2ADMIN.ACAGENTTREE
                             1730802      0  25762  25763      - 8.33e+08   0  98 100 --- 
----------------------------------------------------------------------------------------

Index statistics:

F4: CLUSTERRATIO or normalized CLUSTERFACTOR > 80
F5: 100 * (Space used on leaf pages / Space available on non-empty leaf pages) > MIN(50, (100 - PCTFREE))
F6: (100 - PCTFREE) * (Amount of space available in an index with one less level / Amount of space required for all keys) < 100
F7: 100 * (Number of pseudo-deleted RIDs / Total number of RIDs) < 20
F8: 100 * (Number of pseudo-empty leaf pages / Total number of leaf pages) < 20

SCHEMA.NAME                 INDCARD  LEAF ELEAF LVLS  NDEL    KEYS LEAF_RECSIZE NLEAF_RECSIZE LEAF_PAGE_OVERHEAD NLEAF_PAGE_OVERHEAD  PCT_PAGES_SAVED  F4  F5  F6  F7  F8 REORG  
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Table: DB2ADMIN.ACAGENTTREE
Index: DB2ADMIN.SQL220506215117880
                            1730802  2700     0    3     0 1730802           31            31               3938                3938                0  68  91  19   0   0 *---- 
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

CLUSTERRATIO or normalized CLUSTERFACTOR (F4) will indicate REORG is necessary 
for indexes that are not in the same sequence as the base table. When multiple 
indexes are defined on a table, one or more indexes may be flagged as needing 
REORG.  Specify the most important index for REORG sequencing.

Tables defined using the ORGANIZE BY clause and the corresponding dimension 
indexes have a '*' suffix to their names. The cardinality of a dimension index 
is equal to the Active blocks statistic of the table.

[db2inst1@t3-ucm-ucm-rdb ~]$ db2 "SELECT
> CARD,  --记录数量
> FPAGES,  --表所占页面数量,包含删除记录后的空页面
> NPAGES,  --含有记录的页面数量
> OVERFLOW,  --溢出记录数量
> AVGROWSIZE  --平均记录宽度
> FROM
> SYSSTAT.TABLES
> WHERE
> TABSCHEMA = 'DB2ADMIN'
> AND TABNAME = 'ACAGENTTREE'"

CARD                 FPAGES               NPAGES               OVERFLOW             AVGROWSIZE
-------------------- -------------------- -------------------- -------------------- ----------
             1730802                25763                25762                    0        481

  1 record(s) selected.

  二、MySQL 中如何找出碎片化严重的表
  https://blog.csdn.net/weixin_42018518/article/details/109303800
  
  INFOMATION_SCHEMA架构下的TABLES或STATISTICS存储这表和索引的统计信息，并提供了show index、ANALYZE TABLE、SHOW TABLE STATUS命令来直接显示结果。
关于 MySQL 中的碎片化，一般有两种方法找出碎片：

1、使用 show table status from db_name like 'tb_name' \G
单个表的碎片化情况查询。如果没有 DML 操作，Data_free 的大小为 0（单位 KB）。

2、查询 information_schema.TABLES 获取表的碎片化信息

mysql> SELECT 
    CONCAT(table_schema, '.', table_name) as 'TABLE_NAME', 
    engine as TABLE_ENGINE,
    table_type as TABLE_TYPE,
    table_rows as TABLE_ROWS, 
    CONCAT(ROUND(data_length / ( 1024 * 1024 * 1024 ), 2), 'G') TABLE_DATA_SIZE, 
       CONCAT(ROUND(index_length / ( 1024 * 1024 * 1024 ), 2), 'G') TABLE_IDX_SIZE, 
    CONCAT(ROUND(( data_length + index_length ) / ( 1024 * 1024 * 1024 ), 2), 'G') 'TOTAL SIZE', 
    ROUND(index_length / data_length, 2)  TABLE_IDX_FRAC, 
    CONCAT(ROUND(( data_free / 1024 / 1024 / 1024),2), 'G') AS TABLE_DATA_FREE 
FROM information_schema.TABLES  
WHERE table_name='message_test_wufei';
+---------------------------+--------------+------------+------------+-----------------+----------------+------------+----------------+-----------------+
| TABLE_NAME                | TABLE_ENGINE | TABLE_TYPE | TABLE_ROWS | TABLE_DATA_SIZE | TABLE_IDX_SIZE | TOTAL SIZE | TABLE_IDX_FRAC | TABLE_DATA_FREE |
+---------------------------+--------------+------------+------------+-----------------+----------------+------------+----------------+-----------------+
| testdb.message_test_wufei | InnoDB       | BASE TABLE |   36302847 | 30.62G          | 6.30G          | 36.92G     |           0.21 | 1.05G           |
+---------------------------+--------------+------------+------------+-----------------+----------------+------------+----------------+-----------------+

三、MySQL 中如何减低表的碎片
在 MySQL 中可以使用 OPTIMIZE TABLE XXXX、ALTER TABLE XXXX ENGINE = INNODB 这两种方法降低碎片