{"id":1031,"date":"2012-07-08T18:45:23","date_gmt":"2012-07-08T22:45:23","guid":{"rendered":"http:\/\/sqlity.net\/en\/?p=1031"},"modified":"2014-11-13T13:57:13","modified_gmt":"2014-11-13T18:57:13","slug":"partitions-boundaries-filgroups","status":"publish","type":"post","link":"https:\/\/sqlity.net\/en\/1031\/partitions-boundaries-filgroups\/","title":{"rendered":"Partitions, Boundaries and Filegroups"},"content":{"rendered":"
\n

Introduction<\/h3>\n

\nEarlier today on twitter I ran across an interesting question. The question was, how to identify all partitions and their boundaries for a given filegroup. The solution is not as trivial as it may sound, so I will expand on it here a little.\n<\/p>\n

Partitions and Filegroups<\/h3>\n

\nFirst we need to find out which filegroup a partition is on. All partitions are listed in the sys.partitions<\/span> view. That view has an object_id<\/span> column that we can use to join to sys.tables<\/span>. Joining to sys.tables<\/span> makes sure we are dealing only with partitions of user tables. sys.partitions<\/span> has a hobt_id<\/span> column that allows us to join to sys.allocation_units<\/span> on its container_id<\/span> column. Each table and each index has at least one partition. All normal data pages of a partition are stored together in a single allocation unit. The sys.allocation_units<\/span> view also has a data_space_id<\/span> column that can be used to join to sys.filegroups<\/span>.\n<\/p>\n

Partition Functions<\/h3>\n

\nTo get from a partition to its partition function we need to first join sys.partitions<\/span> with sys.indexes<\/span> on both the object_id<\/span> and on the index_id<\/span> columns. sys.indexes<\/span> also has a data_space_id<\/span> column that we can use to join to sys.partition_schemes.data_space_id<\/span>. From sys.partition_schemes<\/span> we get to sys.partition_functions<\/span> using the function_id<\/span> column of both tables.\n<\/p>\n

Boundaries<\/h3>\n

\nA partition function defines the boundaries of the partitions. The first partition does not have a lower boundary and the last partition does not have an upper boundary. Wether the boundary value itself belongs to its left or its right partition is specified by the LEFT<\/span> or the RIGHT<\/span> key word that was used at the time the partition function was created. It is always the same for all boundaries of a single partition function. Which one was used can be seen in the boundary_value_on_right<\/span> column of the sys.partition_functions<\/span> view. The actual boundary values can be found in the value<\/span> column of the sys.partition_range_values<\/span> view.\n<\/p>\n

\nAs each partition has up to two boundaries, we need to join to sys.partition_range_values<\/span> twice. The function_id<\/span> column ties it to the sys.partition_functions<\/span> view. The boundary_id<\/span> can be correlated with the partition_number<\/span> column of sys.partitions<\/span>. The first partition has boundary one as upper boundary; the second partition has boundary one as lower boundary and boundary two as upper boundary. So for the lower boundary the join condition has to be sys.partition_range_values.boundary_id + 1 = sys.partitions.partition_number<\/span> and for the upper boundary it is sys.partition_range_values.boundary_id = sys.partitions.partition_number<\/span>.\n<\/p>\n

Final Solution<\/h3>\n

\nWhen putting this all together, you need to pay attention to the fact, that while every table has at least one partition, not everyone is located on a partition scheme. Also, not every partition of a partitioned table has both the upper and the lower boundary defined. That means that the four joins to the partition scheme related views have to be outer joins.\n<\/p>\n

\nThe final query can be found below.\n<\/p>\n

\n[sql]\nSELECT f.data_space_id,
\n f.NAME AS file_group_name,
\n SCHEMA_NAME(t.schema_id) AS table_schema,
\n t.name AS table_name,
\n p.partition_number,
\n ps.name AS partition_schem_name,
\n pf.name AS partition_function_name,
\n pf.boundary_value_on_right,
\n left_prv.value AS left_range,
\n right_prv.value AS right_value,
\n ISNULL(STR(CAST(left_prv.value AS BIGINT)), '-INF')
\n + CASE WHEN pf.boundary_value_on_right = 0 THEN ' < '
\n ELSE ' <= '
\n END + 'X' + CASE WHEN pf.boundary_value_on_right = 0 THEN ' <= '
\n ELSE ' < '
\n END + ISNULL(STR(CAST(right_prv.value AS BIGINT)), 'INF') AS range_desc
\nFROM sys.partitions p
\nJOIN sys.tables t
\n ON p.object_id = t.object_id
\nJOIN sys.indexes i
\n ON p.object_id = i.object_id
\n AND p.index_id = i.index_id
\nJOIN sys.allocation_units au
\n ON p.hobt_id = au.container_id
\nJOIN sys.filegroups f
\n ON au.data_space_id = f.data_space_id
\nLEFT JOIN sys.partition_schemes ps
\n ON ps.data_space_id = i.data_space_id
\nLEFT JOIN sys.partition_functions pf
\n ON ps.function_id = pf.function_id
\nLEFT JOIN sys.partition_range_values left_prv
\n ON left_prv.function_id = ps.function_id
\n AND left_prv.boundary_id + 1 = p.partition_number
\nLEFT JOIN sys.partition_range_values right_prv
\n ON right_prv.function_id = ps.function_id
\n AND right_prv.boundary_id = p.partition_number;
\n[\/sql]\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

This post shows a way to link table and index partitions in SQL Server to their filegroups as well as their boundary values. 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