java - What does Oracle CONCURRENCY_WAIT_TIME mean here? -


question

  • for simple select query takes longer concurrency_wait_time, while accessing table not inserted, updated, or deleted, there way can kind of dirty read row in specific table in oracle?
  • what concurrency_wait_time mean here exactly? can guess concurrency_wait_time occur when accessing same row(record) on table multiple sessions? when using read only?

situation

i've been doing load tests on web , rest api server, found simple select query taking time longer expected.

how it's tested

  • jmeter desktop, 500 concurrent post request repeat 3 times , more

throughput result

  • 30/sec when use 100 maxactive per instance
  • 22/sec when use 200 maxactive per instance

how find slow query

  1. spring aspectj on application write method process time @around annotation
  2. python script analyze log rank list methods avg, min, max time
  3. found db select calls take long (2~20 secs) takes less second.
  4. look v$sqlarea find slow query
  5. top 4 queries found average time 2076 ms, had 1970 ms concurrency_wait_time

enter image description here

concurrency_wait_time : concurrency wait time (in microseconds)

oracle v$sqlarea definition

i recommend looking bottleneck somewhere else looking into:

concurrency_wait_time : concurrency wait time (in microseconds)

microsecond 1 millionth of second should not cause significant delays, internal oracle synchronisation mechanism based on i.e. latches, simple , fast.

  1. ensure have baseline os health metrics monitoring in place both java application server , database server, maybe reason banal lack of resources (cpu, ram, network or disk). can use jmeter perfmon plugin this.
  2. if systems not overloaded , still not happy processing time consider using java profilers yourkit or jprofiler find associated heavy methods.
  3. finally can report slow queries dbas take ways of queries optimization.

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