Deleting Lots Of Data

Kenneth Fisher wants to delete a lot of rows:

I recently had the task of deleting a bit over a billion rows from a table. Now I could have done just this:

DELETE FROM tablename WHERE createdate >= '1/1/2017'

But I have a few problems here. The table has no index on createdate, potentially causing problems with tempdb (the sort on createdate). Although in this case tempdb is pretty large because of some large batch work done at various times. I’m also going to be deleting > billion rows of ~6 billion which is probably going to fill up the log of the database (which fortunately isn’t in use yet) and end up rolling back my delete anyway. Even if I don’t fill up the log, I’m still going to bloat it pretty badly (autogrowth). And last, and anything but least, this is on a production server. Even if this database was on its own drive (meaning growth of the log can’t cause a problem with any other databases) that tempdb thing (let alone other resource usage) is going to be an issue.

Read on to see how to delete in batches.  My pattern is to have an explicit transaction within the WHILE loop, opening and closing for each deletion operation.  That has worked pretty well in the past when deleting large numbers of rows from a table.  It might also make sense to put a temporary filtered index on the table, dropping it afterward.

Related Posts

External Memory Pressure In SQL Server 2019 On Linux

Anthony Nocentino walks us through memory pressure in SQL Server on Linux: Now in SQL Server 2017 with that 7GB program running would cause Linux to need to make room in physical memory for this process. Linux does this by swapping least recently used pages from memory out to disk. So under external memory pressure, let’s look […]

Read More

Automating Azure SQL Database Scaling

Arun Sirpal shows how to use Azure Logic Apps to auto-scale Azure SQL Database: When I was presenting my Azure SQL Database session at DataRelay (used to be SQLRelay) I was asked (over coffee) about auto scaling capabilities. Quite simply there is nothing out of the box to achieve this. The idea of auto scaling […]

Read More

Categories

April 2018
MTWTFSS
« Mar May »
 1
2345678
9101112131415
16171819202122
23242526272829
30