Reasonable or Unreasonable Memory occupation?

Couchbase Server
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  • We have 3 nodes with 16GB memory and 100GB disk for data.
  • Each node hosts around 30M documents
  • each documents has 6 fields or so.
  • We have one view, no index
    function (doc,meta) {
    if (doc.className == “something”) {
    emit(doc.ui, {ui: doc.ui, ts: doc.ts}
    }
    }
  • Looking at the memory consumption the meta data (other data) seems to explode

Is it rather weird or as expected, i.e. we are really running low in ressources?
I also start getting Memory warnings: Metadata overhead warning. Over 50% of RAM allocated to bucket “dump” on node “172.x.x.x” is taken up by keys and metadata.

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The metadata cost (in bytes) is approximately:

number_of_documents * (average_key_length + 100) * (1 + replica_count)

I looks like you don’t have replicas configured; and assuming a key length of say 20 bytes that would come out at approximately:

30,000,000 * (20 + 100) 
~= 3.6GB per node.

Given you have ~11GB per-node Bucket Quota (or which ~50% is currently used), my rough numbers would put you at around 60% of RAM used for metadata.

This isn’t necessarily an issue; assuming your dataset isn’t growing; it’s just highlighting that a large percentage is used for storing metadata. Couple of suggestions:

  • Increase the bucket quota to make more available for values.
  • Look into using Full Eviction instead of Value Eviction; note there’s trade-offs in each mode.
1 Like
3

Thanks for your answer. This is actually quite helpful. I was just surprised of the metadata growing so quickly.

In fact we are growing around 10M documents a day.
I guess, the recommendation is probably to just add more nodes going along more data?

To understand correctly:

  • Increasing the quota for data may help in keep the meta data in control?
  • “Full Eviction instead of Value Eviction”: What do you mean here, emitting the entire document in the view?
  • yes, we have no replication.
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See Couchbase SDKs