Deadlock Detection | Oracle Scratchpad on Deadlock Caused by Row Cache and Library Cache Locks.

WINDOW SORT PUSHED RANK Performance Regression in Oracle 21c.

Troubleshooting ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired.

Kernel Memory Leak due to ACFS Snapshots.

Undocumented Implicit Partition Statistics Gathering.

A Data Model Fix for Suboptimal Semi-Join and Anti-Join Cardinality Estimates.

Bind Variable Length in PL/SQL, C, Java and Python.

Performance Improvement on Dictionary Views in Oracle 21c.

Millsap, Mastering Oracle Trace Data, 2nd edition. Convert the timestamp to the human readable format ( convert_tim_to_localtime.py tim t_hr0). Get the high-resolution time reference in Unix Epoch Time ( get_t_hr0.c)ģ. In summary, take the following steps to convert the timestamp from SQL trace ( tim) to the human readable format:ġ. The script takes the timestamp from SQL trace and high-resolution reference time expressed in Unix Epoch time (in microseconds) as its arguments, sums them and displays the time in a human readable format. Another possible source of error is a wall clock time drift, so it’s best to run get_t_hr0 during or immediately after tracing.įinally, convert_tim_to_localtime.py converts the timestamp from the trace file to a human readable format. However, as the program is written in C, this error is negligible. Of course, there’ll inevitably be some marginal error, because the calls to get the current high-resolution and Unix Epoch time are executed sequentially. The returned time is in microseconds – to match the timestamp in the SQL trace. So, I wrote get_t_hr0.c which, basically, gets the current Unix Epoch and high-resolution times and calculates their difference: get_t_hr0 1558015736559599 The equation (2) tells us that, if we get both Unix Epoch and high-resolution time at the “same” time, we can calculate the high-resolution reference time in Epoch.

While t_hr and t_epoch(t_hr) can be easily retrieved from OS, t_epoch(0) is unknown.īut, the equation (1) can be rewritten as follows: T_epoch(0) : high-resolution reference time expressed as UNIX Epoch time.Īs the units in both time systems are the same, any high-resolution time t_hr can be converted to Unix Epoch time as follows: T_epoch(t_hr): current time expressed as UNIX Epoch time, I visualized both time systems in order to work out the high-resolution time reference point: In other words, although the reference point is arbitrary, it doesn’t change over time until the server reboot.

Hi-res timer is ideally suited to performance measurement tasks, whereĬheap, accurate interval timing is required. To resetting or drifting by way of adjtime(2) or settimeofday(3C). Not correlated in any way to the time of day, and thus is not subject It does not necessarily represent time elapsed since boot, nor it is Time is expressed as nanoseconds since some arbitrary time in the past. The gethrtime() function returns the current high-resolution real time. The other is that, unlike wall clock time, high-resolution time isn’t a subject to adjustments:

All programs compile on Linux and Solaris – I used conditional compiling for calling specific low-level OS kernel functions.īut, in the first place, why would somebody use arbitrary timestamps instead of wall clock time for measuring time intervals? One reason is efficiency – the former introduces far less overhead, which can be easily measured with benchmark_timer.c: benchmark_timer I chose C because of its low overhead, which is relevant when measuring time in microseconds. In this blog post, I’ll be presenting the methodology I came up with, and provide a couple of C programs as well. However, once I had to correlate a single wait event outlier to OS performance data and ASH, and therefore, had to find a way to convert the high-resolution time to a human readable format. Normally, that isn’t an issue, because high-resolution timestamps are used for measuring intervals, not for timestamping. Consequently, it can’t be simply converted to Unix Epoch time. In other words, it isn’t correlated in any way to the time of the day or boot time. The high-resolution time is elapsed time since some arbitrary time in the past. This timestamp is derived from an OS kernel high-resolution time.

Convert epoch time to wall clock