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Database / CouchDB Interview Questions

What are the key CouchDB configuration parameters to tune for production (max_dbs_open, os_process_limit, etc.)?

CouchDB's default configuration targets a single-developer workstation. Production deployments require tuning several parameters across different configuration sections:

Key CouchDB Production Configuration Parameters
Section / KeyDefaultWhat it controls
[couchdb] max_dbs_open500Maximum number of database files open simultaneously. Each open database holds a file descriptor. Increase for servers with many databases; ensure OS ulimits allow it.
[couchdb] os_process_limit100Maximum JavaScript OS processes for the query server (views, VDU). Each concurrent JavaScript request consumes one process. Increase for high-concurrency view workloads.
[chttpd] workers100HTTP request handler pool size. Increase for high concurrent request rates.
[couch_httpd_auth] timeout600Session cookie timeout in seconds.
[smoosh] *variousAuto-compaction daemon thresholds. min_priority controls when a database qualifies for compaction based on data/file size ratio.
[rexi] buffer_count2000Internal message buffer for cluster inter-node RPC. Increase if you see rexi_buffer errors in logs.
[fabric] request_timeout60000msTimeout for cluster-level requests. Increase for slow queries over large datasets.

OS-level tuning is equally important: set ulimit -n to at least 65535 for file descriptors (each open database + each view index file counts). On Linux, set vm.swappiness=1 to prevent Erlang heap from being swapped. For high write throughput, ensure the storage device has noatime mount option to avoid inode update I/O on every read.

What does the CouchDB [couchdb] max_dbs_open parameter control?
What resource does each active CouchDB JavaScript query server process consume that requires os_process_limit tuning?

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