The -Z flag specifies optional, comma-separated key-value configuration parameters, called "proxy_behavior"'s in the codebase. For example:

-Z downstream_max=8,time_stats=1,downstream_protocol=ascii

Here's some of the more useful -Z flags:

port_listen                 // IL: Default port to listen on.
cycle                       // IL: Clock resolution in millisecs.
downstream_max              // PL: Downstream concurrency per worker thread.
downstream_retry            // SL: How many times to retry a cmd, defaults to 1.
downstream_protocol         // SL: Favored downstream protocol, defaults to binary.
downstream_timeout          // SL: Millisecs.
wait_queue_timeout          // PL: Millisecs.
time_stats                  // IL: Capture timing stats (for histograms).

connect_max_errors          // IL: Pause when too many connect() errors.
connect_retry_interval      // IL: Time in millisecs before retrying
                            // when too many connect() errors, to not
                            // overwhelm the downstream servers.

front_cache_max             // PL: Max # of front cachable items.
front_cache_lifespan        // PL: In millisecs.
front_cache_spec            // PL: Matcher prefixes for front caching.
front_cache_unspec          // PL: Don't front cache prefixes.

key_stats_max               // PL: Max # of key stats entries.
key_stats_lifespan          // PL: In millisecs.
key_stats_spec              // PL: Matcher prefixes for key-level stats.
key_stats_unspec            // PL: Don't key stat prefixes.

optimize_set                // PL: Matcher prefixes for SET optimization.

usr                         // SL: User name for REST or SASL auth.
pwd                         // SL: Password for REST or SASL auth.
bucket                      // SL: Bucket name for bucket selection.

default_bucket_name         // ML: The named bucket (proxy->name)
                            // that upstream conn's should start on.
                            // When empty (""), then only binary SASL
                            // clients can actually do anything useful.

The IL/ML/PL/SL markers above in the -Z flags refer to a behavior inheritance design in moxi. More information on how behavior/configuration values are inherited at various levels in the system (initialization-level, pool-level, server-level...) is available at:

http://github.com/couchbase/moxi/blob/master/doc/moxi/configuration.org