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From Boyan Kolev <bko...@leanxcale.com>
Subject Problem querying a sharded MongoDB cluster
Date Wed, 14 Oct 2020 16:20:15 GMT
Hello,

I am running a MongoDB cluster with 8 shards (8 mongod instances running on
the same machine) and one mongo router.
On the same machine, there is a drillbit started.
I have enabled the mongodb storage, pointing it to the mongos router
through the "connection" configuration parameter.
There is a sharded collection named customer.

1) SELECT COUNT(*) FROM CUSTOMER
works as expected, i.e. returns the total number of docs, e.g. 1200000;

However:

2) SELECT * FROM CUSTOMER
returns no rows;

3) SELECT * FROM CUSTOMER WHERE c_custkey = 1503;
returns no rows too;

If I connect with mongo shell to the mongo router:

4) db.customer.find({c_custkey: 1503})
returns 1 row as expected;

If I update the mongodb storage configuration to point directly to a mongod
shard instance instead of the mongo router, queries 2) and 3) work
correctly;

Any help to make Drill query correctly (and hopefully in parallel) mongodb
shards will be appreciated.

Thanks,

--
Boyan Kolev

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