Hello, is there a way to limit the maximum number of memory mapped files that quest db leaves in memory?

Hi @Matthew Halko. Do you mean the number of file descriptors or the amount of memory used to mmap them ? The former is generally a function of number of workers x number of tables . The latter could use all available free memory but should release it if there's pressure . You could set memory limit with qdb running in docker though .

ulimit on linux allows both limiting the amount of memory and number of open files on a per process basis: https://ss64.com/bash/ulimit.html I think it's -n and -m

I am on windows server 2019. I have a very simple database setup, a single table with time and sales data. As I query the database, questdb leaves files in memory and eventually will consume all the memory on the machine

Mmaped files are held by cached readers and writers . You can make questdb release them earlier by changing these server.conf properties :

# how often the writer maintenance job gets run,  in milliseconds
#cairo.idle.check.interval=300000

# defines frequency with which the reader pool checks for inactive readers. In milliseconds
#cairo.inactive.reader.ttl=120000

# defines frequency with which the writer pool checks for inactive readers. In milliseconds
#cairo.inactive.writer.ttl=600000

Are you getting memory errors from other applications running on the same box once questdb consumes all memory ?

That worked!

Keep in mind that mmaping a file is slow in Windows so releasing readers more often is likely to slow down queries .

ahhh