Hello Remi,
Am 15.05.20 um 16:10 schrieb Remi Gacogne via Pdns-dev:
Hi Oliver,
In itself, opening the CDB file is not an expensive operation, it mostly
consists of one stat() call to see if the file exists, one open() call
to open it then one mmap() call to map the content of the file into the
memory of the process. Doing that once per minute should not be too bad,
it might be perceptible on the latency on the request triggering the
reload but that should not kill your performance since dnsdist does not
parse the whole file at once. Note however that the content of the new
file might not be in the file system cache, so there might a noticeable
cost when subsequent queries trigger a cache miss, asking the content of
the file to be loaded from the disk into memory. Whether that cost will
make a noticeable impact mostly depends on the size of your file and the
memory pressure of your system, a small file (~a few MBytes) will likely
still have its content loaded in cache if it was very recently generated
or copied.
thanks, this assessment helps me to understand the CDB format and its
internal working.
Is there any reason you are not considering KVS with LMDB instead? For a
database whose content changes that often, that might be a better option.
Yes, but just my little knowledge about LMDB and my wrong thinking. I
thought that this would be a "static" file which is read by dnsdist only
once on startup.
But after a closer look, this seems to be exactly what we need. Thanks
for your hints! I think we will try LMDB.
Wish you all the best,
Oliver
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