The main idea is to log queries that take "too long" to complete.
The "too long" is above the given threshold.
To achieve the above this patch does the following:
- Introduce two new properties to the tracing::trace_state:
- "Full tracing": when the tracing of this query was explicitly requested.
In this state we will record all possible traces related to this query:
both on the coordinator and on any replica involved.
- "Log slow query": when slow query logging is enabled.
If slow query logging is enabled and a session's "duration" is above
the specified threshold we will create a record in the "slow queries log"
and write all trace records created on the coordinator and on a replica
if a replica's session lasts longer than that threshold.
(We will propagate the Coordinator's slow query logging threshold to replicas
in the context of a specific tracing/logging session).
The properties above are independent, namely they may be enabled and/or disabled
independently and any combination of them is legal (naturally, creating a tracing
session when both states above are disabled makes no sense).
- Instrument the tracing::tracing service to allow the following:
- Enable/disable slow query logging.
- Set/get the slow query duration threshold (in microseconds).
- Set/get the slow query log record TTL value (in seconds).
- Instrument the trace_keyspace_helper to write a slow query log entry
when requested.
- The slow query logging is disabled by default and the threshold is set to half a second.
- The TTL of a slow log record is set to 86400 seconds by default.
- It makes sense to use the same "slow query logging threshold" and a "slow query record TTL"
both on a coordinator and on a replica Nodes in a context of the same tracing session:
- Pass both TTL and a threshold to the replica in a trace_info.
This patch also implements the new slow query logging specific logic:
- Don't write the pending tracing records before the end of a tracing session
until "duration" reaches the logging threshold.
- Don't build the parameters<sstring, sstring> map unless we know we will write it
to I/O.
Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
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