Blog Post: How To Split Non-Empty Partitions When A Clustered Columnstore Index Exists on The Table

Another pithily titled blog post, but this one revisits the feature of SQL Server 2014 that piqued my interest the most: Clustered Columnstore Indexes. I’ve been working with Clustered Columnstore Indexes for the past few months and recently a colleague had to split a non empty partition, only for the error message below to appear. Msg 35346, Level 15, State 1, Line 390 SPLIT clause of ALTER PARTITION statement failed because the partition is not empty. Only empty partitions can be split in when a columnstore index exists on the table. Consider disabling the columnstore index before issuing the ALTER PARTITION statement, then rebuilding the columnstore index after ALTER PARTITION is complete. Ok, so it looks like we cannot split non empty partitions with a Clustered Columnstore Index on the table, or at least an enabled clustered columnstore index. So the topic for todays post is to find out how can we split a non empty partition when a clustered columnstore index exists on the table. We can create a test database/tables/Clustered Columnstore Indexes and disable the indexes before we split to see if that is the solution, as suggested in the error that it might be. Let’s start at the beginning using the database I created for my previous post on  SQL Server 2014 Clustered Columnstore Indexes and Partitioning . The script below will create the database and the objects necessary. I’m going to state the obvious, but read through the scripts first before you run them; things like file locations on boxes are always different: /* *************** CREATE DATABASE *************** */ CREATE DATABASE [Phoebix] CONTAINMENT = NONE ON PRIMARY ( NAME = N'Phoebix', FILENAME = N'C:\Program Files\Microsoft SQL Server\MSSQL12.MSSQLSERVER\MSSQL\DATA\Phoebix.mdf' , SIZE = 5120KB , FILEGROWTH = 1024KB ) LOG ON ( NAME = N'Phoebix_log', FILENAME = N'C:\Program Files\Microsoft SQL Server\MSSQL12.MSSQLSERVER\MSSQL\DATA\Phoebix_log.ldf' , SIZE = 2048KB , FILEGROWTH = 10%) GO ALTER DATABASE [Phoebix] SET COMPATIBILITY_LEVEL = 120 GO ALTER DATABASE [Phoebix] SET READ_WRITE GO ALTER DATABASE [Phoebix] SET RECOVERY SIMPLE GO ALTER DATABASE [Phoebix] SET MULTI_USER GO /* *************** CREATE FILEGROUPS *************** */ USE [Phoebix] GO IF NOT EXISTS (SELECT name FROM sys.filegroups WHERE is_default=1 AND name = N'PRIMARY') ALTER DATABASE [Phoebix] MODIFY FILEGROUP [PRIMARY] DEFAULT GO use Phoebix go ALTER DATABASE Phoebix ADD FILEGROUP [FGPhoebix] /* *************** CREATE FILES *************** */ ALTER DATABASE Phoebix ADD FILE (NAME = N'Phoebix_F01', FILENAME = N'S:\Data\PhoebixData\Phoebix1.ndf', SIZE = 5GB, FILEGROWTH = 1GB) TO FILEGROUP [FGPhoebix] ALTER DATABASE Phoebix ADD FILE (NAME = N'Phoebix_F02', FILENAME = N'S:\Data\PhoebixData\Phoebix2.ndf', SIZE = 5GB, FILEGROWTH = 1GB) TO FILEGROUP [FGPhoebix] /* *************** CREATE PARTITION FUNCTION *************** */ USE Phoebix GO CREATE PARTITION FUNCTION pfnPhoebix (int) AS RANGE LEFT FOR VALUES (12116, 12146, 12765, 13258, 13267, 13278, 13441) GO /* *************** CREATE PARTITION SCHEMA *************** */ USE Phoebix GO CREATE PARTITION SCHEME pscPhoebix AS PARTITION pfnPhoebix ALL TO (FGPhoebix) GO /* *************** CREATE TABLES *************** */ use Phoebix go CREATE TABLE dbo.B_Phoebix ( Id INT NOT NULL, MonthEndDate DATE NOT NULL, memberId BIGINT NOT NULL, BSKey VARCHAR (4) NOT NULL, value FLOAT NOT NULL ) ON pscPhoebix (Id) WITH (DATA_COMPRESSION = PAGE); GO CREATE TABLE dbo.S_Phoebix ( Id INT NOT NULL, MonthEndDate DATE NOT NULL, memberId BIGINT NOT NULL, SbId INT NOT NULL, flow FLOAT NOT NULL, vesting FLOAT NULL ) ON pscPhoebix (Id) WITH (DATA_COMPRESSION = PAGE); GO /* *************** CREATE CLUSTERED COLUMNSTORE INDEXES *************** */ CREATE CLUSTERED COLUMNSTORE INDEX [B_Custard] ON [dbo].[B_Phoebix] WITH (DROP_EXISTING = OFF) GO CREATE CLUSTERED COLUMNSTORE INDEX [S_Custard] ON [dbo].[S_Phoebix] WITH (DROP_EXISTING = OFF) GO This database has two tables sharing the same partition schema, which itself is on its own secondary filegroup. The script will create 7 partitions with distinct ranges. Let’s populate some of those partitions with data. This is going to load into staging tables and switch the tables into the partitions, so we can be confident that everything is set up correctly. /* **************** CREATE LOAD DATA **************** */ CREATE TABLE dbo.B_Phoebix_Load ( Id INT NOT NULL, MonthEndDate DATE NOT NULL, memberId BIGINT NOT NULL, BSKey VARCHAR (4) NOT NULL, value FLOAT NOT NULL ) WITH (DATA_COMPRESSION = PAGE); GO CREATE TABLE dbo.S_Phoebix_Load ( Id INT NOT NULL, MonthEndDate DATE NOT NULL, memberId BIGINT NOT NULL, SbId INT NOT NULL, flow FLOAT NOT NULL, vesting FLOAT NULL ) WITH (DATA_COMPRESSION = PAGE); GO declare @i as int; set @i = 1; begin tran while @i = 3200000 begin INSERT INTO dbo.B_Phoebix_Load (Id, monthEndDate, memberId, bsKey, value) values ( 13258, GETDATE(), RAND ()*12, 'FFOS', RAND ()*13), ( 13267, DATEADD(MONTH,1,GETDATE()), RAND ()*12, 'FFOS', RAND ()*13), ( 13278, DATEADD(MONTH,2,GETDATE()), RAND ()*12, 'FFOS', RAND ()*13) INSERT INTO dbo.S_Phoebix_Load (Id, monthEndDate, memberId, sbId, flow, vesting) values ( 13258, GETDATE(), RAND ()*12, RAND ()*50, RAND ()*13, RAND ()*13), ( 13267, DATEADD(MONTH,1,GETDATE()), RAND ()*12, RAND ()*50, RAND ()*13, RAND ()*13), ( 13278, DATEADD(MONTH,2,GETDATE()), RAND ()*12, RAND ()*50, RAND ()*13, RAND ()*13) set @i = @i + 1; end; commit; /* ************************* LOAD DATA INTO PARTITIONS USING STAGING TABLES ************************* */ /**** RUN 1 ****/ -- create the empty rowset from the table we will switch into select top 0 * into dbo.B_Phoebix_13258 from dbo.B_Phoebix select top 0 * into dbo.S_Phoebix_13258 from dbo.S_Phoebix --do ourselves a favour and make this temporary table as small as possible --and add page compression ALTER TABLE dbo.B_Phoebix_13258 REBUILD WITH (DATA_COMPRESSION = PAGE) ALTER TABLE dbo.S_Phoebix_13258 REBUILD WITH (DATA_COMPRESSION = PAGE) --empty rowset is created on primary by default --move to the filegroup the partitioned table is on ALTER TABLE dbo.B_Phoebix_13258 ADD CONSTRAINT CONS_dbo_B_Phoebix_13258 PRIMARY KEY (Id) on FGPhoebix ALTER TABLE dbo.S_Phoebix_13258 ADD CONSTRAINT CONS_dbo_S_Phoebix_13258 PRIMARY KEY (Id) on FGPhoebix -- we don't need it (or can even keep it as we are adding CCI) ALTER TABLE dbo.B_Phoebix_13258 DROP CONSTRAINT CONS_dbo_B_Phoebix_13258 ALTER TABLE dbo.S_Phoebix_13258 DROP CONSTRAINT CONS_dbo_S_Phoebix_13258 --add constraint on temp table so that we can switch in to main table ALTER TABLE dbo.B_Phoebix_13258 WITH CHECK ADD CONSTRAINT CK_B_Phoebix_13258 CHECK (([Id]=(13258))) ALTER TABLE dbo.S_Phoebix_13258 WITH CHECK ADD CONSTRAINT CK_s_Phoebix_13258 CHECK (([Id]=(13258))) --add data to temp table from loading tables --remember IRL this would be SSIS or HPC or data loader of choice INSERT INTO dbo.B_Phoebix_13258 (Id, monthEndDate, memberId, bsKey, value) select Id, monthEndDate, memberId, bsKey, value from dbo.B_Phoebix_Load WITH (NOLOCK) where id = 13258 INSERT INTO dbo.S_Phoebix_13258 (Id, monthEndDate, memberId, sbId, flow, vesting) select Id, monthEndDate, memberId, sbId, flow, vesting from dbo.S_Phoebix_Load WITH (NOLOCK) where id = 13258 --add CCI CREATE CLUSTERED COLUMNSTORE INDEX [PK_B_Phoebix_13258] ON dbo.B_Phoebix_13258 WITH (DROP_EXISTING = OFF) CREATE CLUSTERED COLUMNSTORE INDEX [PK_S_Phoebix_13258] ON dbo.S_Phoebix_13258 WITH (DROP_EXISTING = OFF) --switch in to main table ALTER TABLE dbo.B_Phoebix_13258 SWITCH TO dbo.B_Phoebix PARTITION $PARTITION.pfnPhoebix(13258) ALTER TABLE dbo.S_Phoebix_13258 SWITCH TO dbo.S_Phoebix PARTITION $PARTITION.pfnPhoebix(13258) DROP TABLE dbo.B_Phoebix_13258 DROP TABLE dbo.S_Phoebix_13258 /**** RUN 2 ****/ -- create the empty rowset from the table we will switch into select top 0 * into dbo.B_Phoebix_13267 from dbo.B_Phoebix select top 0 * into dbo.S_Phoebix_13267 from dbo.S_Phoebix --do ourselves a favour and make this temporary table as small as possible --and add page compression ALTER TABLE dbo.B_Phoebix_13267 REBUILD WITH (DATA_COMPRESSION = PAGE) ALTER TABLE dbo.S_Phoebix_13267 REBUILD WITH (DATA_COMPRESSION = PAGE) --empty rowset is created on primary by default --move to the filegroup the partitioned table is on ALTER TABLE dbo.B_Phoebix_13267 ADD CONSTRAINT CONS_dbo_B_Phoebix_13267 PRIMARY KEY (Id) on FGPhoebix ALTER TABLE dbo.S_Phoebix_13267 ADD CONSTRAINT CONS_dbo_S_Phoebix_13267 PRIMARY KEY (Id) on FGPhoebix -- we don't need it (or can even keep it as we are adding CCI) ALTER TABLE dbo.B_Phoebix_13267 DROP CONSTRAINT CONS_dbo_B_Phoebix_13267 ALTER TABLE dbo.S_Phoebix_13267 DROP CONSTRAINT CONS_dbo_S_Phoebix_13267 --add constraint on temp table so that we can switch in to main table ALTER TABLE dbo.B_Phoebix_13267 WITH CHECK ADD CONSTRAINT CK_B_Phoebix_13267 CHECK (([Id]=(13267))) ALTER TABLE dbo.S_Phoebix_13267 WITH CHECK ADD CONSTRAINT CK_s_Phoebix_13267 CHECK (([Id]=(13267))) --add data to temp table from loading tables --remember IRL this would be SSIS or HPC or data loader of choice INSERT INTO dbo.B_Phoebix_13267 (Id, monthEndDate, memberId, bsKey, value) select Id, monthEndDate, memberId, bsKey, value from dbo.B_Phoebix_Load WITH (NOLOCK) where id = 13267 INSERT INTO dbo.S_Phoebix_13267 (Id, monthEndDate, memberId, sbId, flow, vesting) select Id, monthEndDate, memberId, sbId, flow, vesting from dbo.S_Phoebix_Load WITH (NOLOCK) where id = 13267 --add CCI CREATE CLUSTERED COLUMNSTORE INDEX [PK_B_Phoebix_13267] ON dbo.B_Phoebix_13267 WITH (DROP_EXISTING = OFF) CREATE CLUSTERED COLUMNSTORE INDEX [PK_S_Phoebix_13267] ON dbo.S_Phoebix_13267 WITH (DROP_EXISTING = OFF) --switch in to main table ALTER TABLE dbo.B_Phoebix_13267 SWITCH TO dbo.B_Phoebix PARTITION $PARTITION.pfnPhoebix(13267) ALTER TABLE dbo.S_Phoebix_13267 SWITCH TO dbo.S_Phoebix PARTITION $PARTITION.pfnPhoebix(13267) DROP TABLE dbo.B_Phoebix_13267 DROP TABLE dbo.S_Phoebix_13267 /**** RUN 3 ****/ -- create the empty rowset from the table we will switch into select top 0 * into dbo.B_Phoebix_13278 from dbo.B_Phoebix select top 0 * into dbo.S_Phoebix_13278 from dbo.S_Phoebix --do ourselves a favour and make this temporary table as small as possible --and add page compression ALTER TABLE dbo.B_Phoebix_13278 REBUILD WITH (DATA_COMPRESSION = PAGE) ALTER TABLE dbo.S_Phoebix_13278 REBUILD WITH (DATA_COMPRESSION = PAGE) --empty rowset is created on primary by default --move to the filegroup the partitioned table is on ALTER TABLE dbo.B_Phoebix_13278 ADD CONSTRAINT CONS_dbo_B_Phoebix_13278 PRIMARY KEY (Id) on FGPhoebix ALTER TABLE dbo.S_Phoebix_13278 ADD CONSTRAINT CONS_dbo_S_Phoebix_13278 PRIMARY KEY (Id) on FGPhoebix -- we don't need it (or can even keep it as we are adding CCI) ALTER TABLE dbo.B_Phoebix_13278 DROP CONSTRAINT CONS_dbo_B_Phoebix_13278 ALTER TABLE dbo.S_Phoebix_13278 DROP CONSTRAINT CONS_dbo_S_Phoebix_13278 --add constraint on temp table so that we can switch in to main table ALTER TABLE dbo.B_Phoebix_13278 WITH CHECK ADD CONSTRAINT CK_B_Phoebix_13278 CHECK (([Id]=(13278))) ALTER TABLE dbo.S_Phoebix_13278 WITH CHECK ADD CONSTRAINT CK_s_Phoebix_13278 CHECK (([Id]=(13278))) --add data to temp table from loading tables --remember IRL this would be SSIS or HPC or data loader of choice INSERT INTO dbo.B_Phoebix_13278 (Id, monthEndDate, memberId, bsKey, value) select Id, monthEndDate, memberId, bsKey, value from dbo.B_Phoebix_Load WITH (NOLOCK) where id = 13278 INSERT INTO dbo.S_Phoebix_13278 (Id, monthEndDate, memberId, sbId, flow, vesting) select Id, monthEndDate, memberId, sbId, flow, vesting from dbo.S_Phoebix_Load WITH (NOLOCK) where id = 13278 --add CCI CREATE CLUSTERED COLUMNSTORE INDEX [PK_B_Phoebix_13278] ON dbo.B_Phoebix_13278 WITH (DROP_EXISTING = OFF) CREATE CLUSTERED COLUMNSTORE INDEX [PK_S_Phoebix_13278] ON dbo.S_Phoebix_13278 WITH (DROP_EXISTING = OFF) --switch in to main table ALTER TABLE dbo.B_Phoebix_13278 SWITCH TO dbo.B_Phoebix PARTITION $PARTITION.pfnPhoebix(13278) ALTER TABLE dbo.S_Phoebix_13278 SWITCH TO dbo.S_Phoebix PARTITION $PARTITION.pfnPhoebix(13278) DROP TABLE dbo.B_Phoebix_13278 DROP TABLE dbo.S_Phoebix_13278 Now we have data loaded, we need a method of viewing the partitions. The script below will create a stored proc that we can run to view the data by partition. This sproc is modified from my  SQL Server Partitioning 101  post. /**** ************************************************ CREATE STORED PROC WE CAN VIEW THE PARTITIONS BY ************************************************ ****/ USE Phoebix GO CREATE PROCEDURE [dbo].[LatestPartitionPreview] ( @partitionName nvarchar(100), @sampleTable sysname ) AS declare @sql nvarchar(max) declare @pscName nvarchar(100) declare @pfnName nvarchar(100) SET @pscName = 'psc' + @partitionName SET @pfnName = 'pfn' + @partitionName declare @partitonedTableId int SELECT @partitonedTableId = t.object_id FROM sys.TABLES t with (nolock) JOIN sys.indexes i with (nolock) ON t.object_id = i.object_id JOIN sys.partition_schemes ps with (nolock) ON i.data_space_id = ps.data_space_id WHERE i.index_id 2 and ps.name = @pscName and t.name like @sampleTable + '%' declare @currentPartitions table(partitionNumber int, [rows] int, value sql_variant, ranking int) ;with ranges (boundaryId, value) as ( select prv.boundary_id, prv.value from sys.partition_functions f with (nolock) inner join sys.partition_schemes s with (nolock) on s.function_id = f.function_id inner join sys.partition_range_values prv with (nolock) on prv.function_id = f.function_id where f.name = @pfnName ) INSERT INTO @currentPartitions SELECT partition_number, [rows], [value], ROW_NUMBER() OVER (ORDER BY partition_number desc) ranking FROM (select top 1000 p.partition_number, [rows], [value] FROM sys.partitions p with (nolock) left join ranges on ranges.boundaryid = p.partition_number where p.[object_id] = @partitonedTableId order by p.partition_number desc ) latestPartitions order by partition_number desc select * from @currentPartitions GO Execute the sproc to view the runs by partition: /**** ************************************************ EXECUTE SPROC ************************************************ ****/ USE [Phoebix] GO EXEC [dbo].[LatestPartitionPreview] @partitionName = N'Phoebix', @sampleTable = N'B_Phoebix' GO The result will look the same as this: Ok great, we’ve now got 2 partitioned tables stored as CCI. Now what happens when we try to split a non empty partition? ALTER PARTITION SCHEME pscPhoebix NEXT USED [FGPhoebix]; ALTER PARTITION FUNCTION pfnPhoebix() SPLIT RANGE(13261); I’ve omitted some of the error, it is the same as at the top of the page : Msg 35346, Level 15, State 1, Line 390 SPLIT clause of ALTER PARTITION statement failed because the partition is not empty. Only empty partitions can be split in when a columnstore index exists on the table. Consider disabling the columnstore index before issuing the ALTER PARTITION statement, then rebuilding the columnstore index after ALTER PARTITION is complete. Ok, we’ve got the same error message as before; this is expected as we know we cannot split non-empty partitions on tables that are stored as CCI. The syntax for disabling an index is straightforward, and we need to disable indexes on both tables. ALTER INDEX [B_Custard] ON [dbo].[B_Phoebix] DISABLE GO ALTER INDEX [S_Custard] ON [dbo].[S_Phoebix] DISABLE GO We’ve disabled the index, so let’s try splitting the partition again: ALTER PARTITION SCHEME pscPhoebix NEXT USED [FGPhoebix]; ALTER PARTITION FUNCTION pfnPhoebix() SPLIT RANGE(13261); Ah, looks like disabling does not solve the issue. This is actually documented in the ‘Limitations and Restrictions’ section regarding altering partitions on   Books Online . So this somewhat contradicts the suggestion in the original error message. The error message I got is in full below. Msg 7725, Level 16, State 1, Line 398 Alter partition function statement failed. Cannot repartition table ‘B_Phoebix’ by altering partition function ‘pfnPhoebix’ because its clustered index ‘B_Custard’ is disabled. So, what are we to do? Well the first thing we should do is enable the index. Then we can look into workarounds. ALTER INDEX [B_Custard] ON [dbo].[B_Phoebix] REBUILD GO ALTER INDEX [S_Custard] ON [dbo].[S_Phoebix] REBUILD GO There’s no way around it, we need to drop the index. Or do we? Seeing as we’re using partitioned tables here, the pragmatic, and faster, way of splitting a non-empty partition is to switch out the partition into a staging table, split the now empty partition, and switch the data back in. Really, it’s a case of modifying the import process above. If you get any errors from running the script below, make sure you have rebuilt the indexes after disabling them. -- create the empty rowset from the table we will switch into select top 0 * into dbo.B_Phoebix_13267 from dbo.B_Phoebix select top 0 * into dbo.S_Phoebix_13267 from dbo.S_Phoebix --empty rowset is created on primary by default --move to the filegroup the partitioned table is on ALTER TABLE dbo.B_Phoebix_13267 ADD CONSTRAINT CONS_dbo_B_Phoebix_13267 PRIMARY KEY (Id) on FGPhoebix ALTER TABLE dbo.S_Phoebix_13267 ADD CONSTRAINT CONS_dbo_S_Phoebix_13267 PRIMARY KEY (Id) on FGPhoebix -- we don't need it (or can even keep it as we are adding CCI) ALTER TABLE dbo.B_Phoebix_13267 DROP CONSTRAINT CONS_dbo_B_Phoebix_13267 ALTER TABLE dbo.S_Phoebix_13267 DROP CONSTRAINT CONS_dbo_S_Phoebix_13267 --add CCI CREATE CLUSTERED COLUMNSTORE INDEX [PK_B_Phoebix_13267] ON dbo.B_Phoebix_13267 WITH (DROP_EXISTING = OFF) CREATE CLUSTERED COLUMNSTORE INDEX [PK_S_Phoebix_13267] ON dbo.S_Phoebix_13267 WITH (DROP_EXISTING = OFF) At this juncture we have a staging table that is exactly the same as the main table, so we can now switch the non empty partition we want to split into this new table. ALTER TABLE [dbo].[B_Phoebix] SWITCH PARTITION $PARTITION.pfnPhoebix(13267) TO [dbo].[B_Phoebix_13267] ALTER TABLE [dbo].[S_Phoebix] SWITCH PARTITION $PARTITION.pfnPhoebix(13267) To [dbo].[S_Phoebix_13267] Running the stored proc again will confirm that the partition is now empty: USE [Phoebix] GO EXEC [dbo].[LatestPartitionPreview] @partitionName = N'Phoebix', @sampleTable = N'B_Phoebix' GO Great, split the partition and run the sproc again: ALTER PARTITION SCHEME pscPhoebix NEXT USED [FGPhoebix]; ALTER PARTITION FUNCTION pfnPhoebix() SPLIT RANGE(13261); USE [Phoebix] GO EXEC [dbo].[LatestPartitionPreview] @partitionName = N'Phoebix', @sampleTable = N'B_Phoebix' GO My result is below: We’re nearly done. All we need to do is switch in the staging table and we’ll be back the way we were. ALTER TABLE dbo.B_Phoebix_13267 WITH CHECK ADD CONSTRAINT CK_B_Phoebix_13267 CHECK (([Id]=(13267))) ALTER TABLE dbo.S_Phoebix_13267 WITH CHECK ADD CONSTRAINT CK_s_Phoebix_13267 CHECK (([Id]=(13267))) --switch in to main table ALTER TABLE dbo.B_Phoebix_13267 SWITCH TO dbo.B_Phoebix PARTITION $PARTITION.pfnPhoebix(13267) ALTER TABLE dbo.S_Phoebix_13267 SWITCH TO dbo.S_Phoebix PARTITION $PARTITION.pfnPhoebix(13267) Execute the sproc one last time to verify that the data has been switched in. USE [Phoebix] GO EXEC [dbo].[LatestPartitionPreview] @partitionName = N'Phoebix', @sampleTable = N'B_Phoebix' GO So now we’ve been able to split the partition without having to drop the index. Great! And thanks to partitioning being so quick, it was a swift operation. It would get more complicated if you wanted to split the data in one partition into two partitions as you’d need to split the data out of the staging table into two staging tables, which won’t be as quick an operation as the example above. At any rate, the example above shows that you can avoid having to drop clustered columnstore indexes on tables in order to split non-empty partitions. Follow @rPh0enix