Nick Vatamaniuc created COUCHDB-2959:
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Summary: Deadlock condition in replicator with remote source and
configured 1 http connection
Key: COUCHDB-2959
URL: https://issues.apache.org/jira/browse/COUCHDB-2959
Project: CouchDB
Issue Type: Bug
Components: Replication
Reporter: Nick Vatamaniuc
A deadlock that occurs that can get the starting replications to get stuck (and
never update their state to triggered). This happens with a remote source and
when using a single http connection and single worker.
The deadlock occurs in this case:
- Replication process starts, it starts the changes reader:
https://github.com/apache/couchdb-couch-replicator/blob/master/src/couch_replicator.erl#L276
- Changes reader consumes the worker from httpc pool. At some point it will
make a call back to the replication process to report how much work it has done
using gen_server call {{report_seq_done}}
- In the meantime, main replication process calls {{get_pending_changes}} to
get changes from the source. If the source is remote it will attempt to
consumer a worker from httpc pool. However the worker is used by the change
feed process. So get_pending_changes is blocked waiting for a worker to be
released.
- So changes feed is waiting for report_seq_done call to replication process
to return while holding a worker and main replication process is waiting for
httpc pool to release the worker and it never responds to report_seq_done.
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