I have a DB with high cardinality (in the process of resolving this; but
trying to export my old data first!)
Per: SELECT sum(numSeries) AS "total_series" FROM "_internal".."database"
WHERE time > now() - 10s
I have 4.2M series.
I'm running on a server with 128GB ram.
Normally, at startup -- it uses 20GB-40GB of ram.
If I run a select statement on a field, RAM usage increases to 56GB, and it
returns the answers.
If I run a select statement on a tag, I get an empty-set returned to me,
after lots of CPU-chugging; but RAM usage doesn't exceed 56GB.
{"results":[{}]}
If I try to run a select statement like select *, RAM usage exceeds 128GB,
swaps another 60GB, never returns.
I'm running 0.13
I understand high cardinality is 'bad' -- but typically recommendations
call for just adding more RAM, and hoping for the best. I've not seen
mention of differentiation in RAM usage based on select parameters, nor the
behavior of returning an empty-set.
All selects are done on a 10min period from two days ago, with typically 3M
data points per day. I use 1d shard size. There's one measurement I'm doing
these selects from. I have a handful of other measurements being generated
by continuous queries.
Using show queries and kill query ID, I can successfully kill the select *
query (no longer shows in show queries) -- however ram usage does not drop;
and I'm forced to restart influxdb to get back to a base-line state.
Is this run-away ram usage considered a bug? or expected behavior somehow
based on cardinality, only triggered by certain select queries?
I've heard of others with higher series cardinality on the list... never
heard them speak of issues like this.
Due to this issue, I'm unable to export my data.
Appreciate any insight; happy to debug further if its a bug, and I can be
of assistance tracking it down (and happy to open a github issue if more
appropriate than discussion here)
Thanks!
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