*`1 errors` -- how many errors there are in total. Action is required for every error, this number must be zero. The number of errors includes slower tests, tests that are too long, errors while running the tests and building reports, etc. Please look at the main report page to investigate these errors.
The report page itself consists of a several tables. Some of them always signify errors, e.g. "Run errors" -- the very presence of this table indicates that there were errors during the test, that are not normal and must be fixed. Some tables are mostly informational, e.g. "Test times" -- they reflect normal test results. But if a cell in such table is marked in red, this also means an error, e.g., a test is taking too long to run.
Informational, no action required. Log messages for the commits that are tested. Note that for the right commit, we show nominal tested commit `pull/*/head` and real tested commit `pull/*/merge`, which is generated by GitHub by merging latest master to the `pull/*/head` and which we actually build and test in CI.
The errors that occurred when running some test queries. For more information about the error, download test output archive and see `test-name-err.log`. To reproduce, see 'How to run' below.
Action required for every item -- these are errors that must be fixed.
This table shows queries that take significantly longer to process on the client than on the server. A possible reason might be sending too much data to the client, e.g., a forgotten `format Null`.
A query is supposed to run longer than 0.1 second. If your query runs faster, increase the amount of processed data to bring the run time above this threshold. You can use a bigger table (e.g. `hits_100m` instead of `hits_10m`), increase a `LIMIT`, make a query single-threaded, and so on. Queries that are too fast suffer from poor stability and precision.
Shows the queries we are unable to run on an old server -- probably because they contain a new function. You should see this table when you add a new function and a performance test for it. Check that the run time and variance are acceptable (run time between 0.1 and 1 seconds, variance below 10%). If not, they will be highlighted in red.
Action required for the cells marked in red, and some cheering is appropriate for the cells marked in green.
These are the queries for which we observe a statistically significant change in performance. Note that there will always be some false positives -- we try to filter by p <0.001,andhave2000queries,sotwofalsepositivesperrunareexpected.Inpracticewehavemore--e.g.codelayoutchangedbecauseofsomeunknowablejitterincompilerinternals,sothechangeweobserveisreal,butitisa'falsepositive'inthesensethatitisnotdirectlycausedbyyourchanges.If,basedonyourknowledgeofClickHouseinternals,youcandecidethattheobservedtestchangesarenotrelevanttothechangesmadeinthetestedPR,youcanignorethem.
You can find flame graphs for queries with performance changes in the test output archive, in files named as 'my_test_0_Cpu_SELECT 1 FROM....FORMAT Null.left.svg'. First goes the test name, then the query number in the test, then the trace type (same as in `system.trace_log`), and then the server version (left is old and right is new).
These are the queries for which we did not observe a statistically significant change in performance, but for which the variance in query performance is very high. This means that we are likely to observe big changes in performance even in the absence of real changes, e.g. when comparing the server to itself. Such queries are going to have bad sensitivity as performance tests -- if a query has, say, 50% expected variability, this means we are going to see changes in performance up to 50%, even when there were no real changes in the code. And because of this, we won't be able to detect changes less than 50% with such a query, which is pretty bad. The reasons for the high variability must be investigated and fixed; ideally, the variability should be brought under 5-10%.
The most frequent reason for instability is that the query is just too short -- e.g. below 0.1 seconds. Bringing query time to 0.2 seconds or above usually helps.
Other reasons may include:
* using a lot of memory which is allocated differently between servers, so the access time may vary. This may apply to your queries if you have a `Memory` engine table that is bigger than 1 GB. For example, this problem has plagued `arithmetic` and `logical_functions` tests for a long time.
* having some threshold behavior in the query, e.g. you insert to a Buffer table and it is flushed only on some query runs, so you get a much higher time for them.
Investigating the instablility is the hardest problem in performance testing, and we still have not been able to understand the reasons behind the instability of some queries. There are some data that can help you in the performance test output archive. Look for files named 'my_unstable_test_0_SELECT 1...FORMAT Null.{left,right}.metrics.rep'. They contain metrics from `system.query_log.ProfileEvents` and functions from stack traces from `system.trace_log`, that vary significantly between query runs. The second column is array of \[min, med, max] values for the metric. Say, if you see `PerfCacheMisses` there, it may mean that the code being tested has not-so-cache-local memory access pattern that is sensitive to memory layout.
Shows the tests that were skipped, and the reason for it. Normally it is because the data set required for the test was not loaded, or the test is marked as 'long' -- both cases mean that the test is too big to be ran per-commit.
This table summarizes the changes in performance of queries in each test -- how many queries have changed, how many are unstable, and what is the magnitude of the changes.
1) Average query run time is too long -- probably means that the preparatory steps such as creating the table and filling them with data are taking too long. Try to make them faster.
2) Longest query run time is too long -- some particular queries are taking too long, try to make them faster. The ideal query run time is between 0.1 and 1 s.
These are changes in median values of metrics from `system.asynchronous_metrics_log`. These metrics are prone to unexplained variation and you can safely ignore this table unless it's interesting to you for some particular reason (e.g. you want to compare memory usage). There are also graphs of these metrics in the performance test output archive, in the `metrics` folder.
#### Errors while Building the Report
Ask a maintainer for help. These errors normally indicate a problem with testing infrastructure.
1\. Box, Hunter, Hunter "Statistics for exprerimenters", p. 78: "A Randomized Design Used in the Comparison of Standard and Modified Fertilizer Mixtures for Tomato Plants."
