Hi !
I'm working with @adrienverge and I continue to investigate the "black matter"
issue.
As @adrienverge said, shard files (`db.1520354435.couch`) constantly keep
growing (by several kB per day), even though there are no requests done to them.
This is a problem because we have *many* small, untouched databases.
Compaction helps to free space on a regular basis, but it takes a bunch of cpu
time.
So we would like to understand what is happening in our `.couch` files.
In a node of our cluster we monitored output of `strings
/var/lib/couchd/shards/xxx/db.1520354435.couch`.
In one night, it had ~800 new rows like this one:
```
kv_nodel
?_local/shard-sync-VNaRvSQnMLpUSzV8iZvcow-IOHL5NIdglwNQCT0DL_V0Ah
seqa} ],
target_uuid
cef8fe0a2eac1f0f7af0d5e0c56fbbd8 7
historyh
@;couchdb@node1l
142-216
-$!7
source
x2a65d174d772861e4cd085e9e347729-
$ timestamp!7|
2018-10-02T22:21:13.181557Zjjjj ~Jd
TgKo_QqiB9XPEFr08HvUC2Q
98-214
M/Uf|e0dc03c296d3847efd92e964053e5f1b 7
P15:23:01.533200Zjjjjj
kp_nodel
?_local/shard-sync-IOHL5NIdglwNQCT0DL_V0A-gKo_QqiB9XPEFr08HvUC2Qh
-IOHLFj
db_headera
size_infob
nilb
cef8fe0a2eac1f0f7af0d5e0c56fbbd8l
<couchdb@node2a
```
As we have ~34k dbs, multiplied by 8 shards by node, it quickly sum up and
takes a lot of space and a lot of compaction time, which sometimes ends up
saturating our disks and CPU.
Can you advise us ?
[ Full content available at: https://github.com/apache/couchdb/issues/1621 ]
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