Hello, I'm still a bit confused with shards versus partitions, is this
correct ?
- A database is composed of Q shards, shards splice the database
"automatically"
- A shard is composed of 1 or more partitions, partitions splice the
database according to the user's choice. A partition should thus be made
so that it is not huge, in fact must be under (total size/Q)
- When querying a view, the whole database needs to be processed, that
means all Q shards
- When querying a view only on documents inside a partition, since one
partition is on 1 shard, only one shard is queried
- Whatever the number of shards, quorum still needs to be verified, ie
for Q=2 and N=3 I still need to wait for (3+1)/2 = 2 replies for each shard
On 12/06/2024 19:54, Nick Vatamaniuc wrote:
Another feature related to efficient view querying are partitioned
databases: https://docs.couchdb.org/en/stable/partitioned-dbs/index.html.
It's a bit of a niche, as you'd need to have a good partition key, but
aside from that, it can speed up your queries as responses would be coming
from a single shard only instead of Q shards.
On Wed, Jun 12, 2024 at 1:30 PM Markus Doppelbauer
<[email protected]> wrote:
Hi Nick,
Thank you very much for your reply.This is exactly what we are looking
for.There are so many DBs that store the secondary indexlocally
(Cassandra, Aerospike, SyllaDB, ...)
Thanks again for the answerMarcus
Am Mittwoch, dem 12.06.2024 um 13:23 -0400 schrieb Nick Vatamaniuc:
Hi Marcus,
The node handling the request only queries the nodes with shard
copies ofthat database. In a 100 node cluster the shards for that
particulardatabase might be present on only 6 nodes, depending on the
Q and Nsharding factors, so it will query 6 out 100 nodes. For
instance, for N=3and Q=2 sharding factors, it will first send N*Q=6
requests, and wait untilit gets at least one response for each of the
Q=2 shard ranges. Thishappens very quickly. Then, for the duration of
the response, it will onlystream responses from those Q=2 workers.
So, to summarize for a Q=2database, it will be a streaming response
from 2 workers. For Q=4, from 4workers, etc...
Cheers,-Nick
On Wed, Jun 12, 2024 at 1:00 PM Markus Doppelbauer<
[email protected]> wrote:
Hello,
Is the CouchDB-view a "global" or "local" index?For example, if a
cluster has 100 nodes, would the query askfor a single node - or
100 nodes?
/.../_view/posts?startkey="foobar"&endkey="foobaz"
Best wishesMarcus
