SQL Server Table with 4 Million Rows – 40GB Size Analysis

database-sizeperformancesql server

I have been trying to figure out why our production database has grown so much recently and have found the cause to be an audit table. We are going to archive the table to fix the problem but I just wanted to check if the size of the table looked normal for a large SQL server table like this.
It has 4,000,000 rows with the following structure…

Name                    Type        Nullable
AuditLogId              bigint      no
UserName                nvarchar    no
TimeOfChange            datetime    no
ObjectName              nvarchar    no
ChangeName              nvarchar    no
RecordId                int         yes
OriginalValues          nvarchar    yes
ResultingValues         nvarchar    no

With a primary key on the AuditLogId

ALTER TABLE [dbo].[AuditLog] ADD  CONSTRAINT [PK_AuditLog] PRIMARY KEY CLUSTERED 
(
    [AuditLogId] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 80) ON [PRIMARY]
GO

There is also a foreign key to the record that was updated on RecordId.
The nvarchar fields seem to have up to 12,0000 characters with an average of around 8000 characters.
The table is currently 40GB in size, does that seem right? I can provide more information on the table if that question can’t be answered with what I have posted above.

Thanks

Best Answer

You have 4,000,000 rows and one of the columns averages 8,000 characters (16,000 bytes, I assume).

SELECT CONVERT(bigint,4000000) * /* b */ 16000 / /*kb*/ 1024 / /*mb*/ 1024;
------
61,035

If your stats are accurate, I'd expect this table to be 61 GB. (I wonder if you mean 8,000 bytes, not 8,000 characters, in which case I'd expect > 30 GB.)

Other factors include:

  • data in other columns I didn't account for in the above calculation
  • additional indexes
  • fill factor > 0 and < 100
  • fragmentation and space still occupied by deleted rows or page splits
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