VdbScan Clean Has Failed

When a query that shouldn’t be using up a lot of memory but is check the network maintenance logs. Especially if it is a read only query. Especially if it seems impossible to recover that memory from within the session.

Troubleshooting

Failing to recover memory within a session looks like:

# run query here
AdminTools displayMemoryStats;
"COLLECTING GARBAGE" printNL;
Utility collectSessionGarbage;
AdminTools displayMemoryStats;

with output:

  Current allocation level:      3,639,834,928
  Session maximum:               3,648,481,697
  Heap limit:                    3,708,354,560
  Total size of mapped segments  8,828,141,976
COLLECTING GARBAGE
  Current allocation level:      3,644,079,204
  Session maximum:               3,648,493,713
  Heap limit:                    3,708,354,560
  Total size of mapped segments  8,828,141,976

The current allocation WENT UP!

Fixing

Here you need to find the underlying structure and force clean to complete on it.

Brute Force cleanSpace

If an ObjectSpace cleanSpace is running out of memory you can try:

• cleaning parts of the space using cleanStore
• forcing parts of the space to be cleaned by accessing those stores then commiting a bit at a time
• increasing the datasize limit and running the cleanSpace

We often use the limit datasize option for the sake of expediency. First you bump the limit datasize by a signficant factor (5x usually) then run the following:

GlobalWorkspace AdminTools setAllocationThresholdTo: 100000000;
10 asObjectSpace cleanSpace;

Which completed successfully. After forcing a cleanSpace to complete a full database clean and GC should be performed to make sure there are no other database problems lurking.