What is "Unaccounted Wait"?
Unaccounted Wait shows the time spent waiting for system calls (mostly blocking I/O), that cannot be accounted for by data collected for the timeline trace, such as SQL queries or HTTP calls.
This is often the case when the servers resources are congested or core system functionality like DNS resolution stall or certain system calls and network I/O blocks. It can also be the case when Tideways is missing automatic instrumentation for a database, cache, or any other kind of service you talk to over using local or network I/O.
Unaccounted Wait is calculated using the following formula:
Wall-Time - CPU-Time - Known I/O operations (e.g., SQL, Memcache, File I/O)To find sources of unaccounted wait time, trigger a trace or add a tracepoints to generate a callgraph that contains all the PHP functions called during a request.