问题描述
我试图在 MSsql 中检索聚集列存储索引所需的确切字节数。 不幸的是,与 sys.allocation_units 上的简单查询相比,我从 sp_spaceused 得到了不同的结果。
这里是简单的脚本:
-- create table
CREATE TABLE TestColumnStore (Id INT IDENTITY(1,1) NOT NULL,Val VARCHAR(128));
CREATE CLUSTERED COLUMNSTORE INDEX [IX_TestColumnStore] ON [TestColumnStore];
GO
-- append 1000 rows
DECLARE @i INT = 0;
WHILE @i < 1000
BEGIN
INSERT INTO dbo.TestColumnStore (Val) VALUES ('Jhon');
SET @i = @i+1;
END
这里是 sp_spaceused
结果:
name rows reserved data index_size unused
---------------- ---------- ----------- ------------- ------------------ ------------------
TestColumnStore 1000 144 KB 48 KB 16 KB 80 KB
然后我尝试使用此查询直接获取已占用页面的数量sys.allocation_units
:
SELECT
al.total_pages * 8 AS TotalSpaceKB,al.used_pages * 8 AS UsedspaceKB,(al.total_pages - al.used_pages) * 8 AS UnusedspaceKB,al.allocation_unit_id,p.partition_id,o.[name],al.type_desc,p.data_compression_desc
FROM
sys.allocation_units al
JOIN sys.partitions p ON al.container_id = p.partition_id
LEFT JOIN sys.objects o ON o.object_id = p.object_id
WHERE
o.name = 'TestColumnStore'
当然,结果显然正是 sp_spaceused 返回的一半。
TotalSpaceKB UsedspaceKB UnusedspaceKB allocation_unit_id partition_id name type_desc data_compression_desc
-------------------- -------------------- -------------------- -------------------- -------------------- --------------------- ------------------ ----------------------
0 0 0 72057594050183168 72057594043629568 TestColumnStore IN_ROW_DATA COLUMNSTORE
72 16 56 72057594050248704 72057594043629568 TestColumnStore LOB_DATA COLUMNSTORE
谁能帮我弄清楚我错过了什么?获取以字节为单位的确切表大小的正确方法是什么?
解决方法
这是返回与 sp_spaceused 完全相同大小的最终查询:
SELECT
SUM(TotalSpaceKB) TotalSpaceKB,SUM(UsedSpaceKB) UsedSpaceKB,SUM(UnusedSpaceKB) UnusedSpaceKB
FROM (
SELECT
al.total_pages * 8 AS TotalSpaceKB,al.used_pages * 8 AS UsedSpaceKB,(al.total_pages - al.used_pages) * 8 AS UnusedSpaceKB,al.allocation_unit_id,p.partition_id,o.[name],al.type_desc,p.data_compression_desc
FROM
sys.allocation_units al
JOIN sys.partitions p ON al.container_id = p.partition_id
JOIN sys.objects o ON o.object_id = p.object_id
WHERE
o.name = 'TestColumnStore'
UNION
SELECT
al.total_pages * 8 AS TotalSpaceKB,NULL AS partition_id,NULL AS data_compression_desc
FROM
sys.column_store_row_groups csrg
JOIN sys.allocation_units al ON al.container_id = csrg.delta_store_hobt_id
JOIN sys.objects o ON csrg.object_id = o.object_id
WHERE
o.name = 'TestColumnStore'
) a
GROUP BY a.name