This commit makes a number of performance improvements to
reduce allocations during query execution. Several objects
and buffers are now reused across the components to avoid
allocations.
Previously a simple `count(value)` query across 1M points
would require 26,000+ allocations. After the changes in
this commit that number has been reduced to 88.
Send nil values from the tsm1 cursor at the end of the cursor. After the
cursor reached tsm1, the `nextAt()` call would always return the default
value rather than a nil value.
Descending also didn't work correctly because the seeking functionality
for tsm1 iterators would always act like they were ascending instead of
descending when choosing which value to select. This resulted in very
strange output from the emitter since it couldn't figure out if it was
ascending or descending.
Fixes#6206.
This commit adds a buffer for stats to be updated without
requiring a mutex lock/unlock on every point. The tradeoff
is that stats are not exactly precise. This works for our
use case because stats are only periodically checked.
After reading the initial buffer, ORDER BY desc would read the next
block into the buffer and only read the first element. It's because the
code that was copied from the ascending cursor wasn't modified correctly
to set the position to the last element in the buffer.
The buffer size has also been lowered from 1000 to 10 to match with the
ascending cursor for performance with limit queries.
Fixes#6055.
This commit adds an `IteratorStats` that holds aggregate
iterator processing information. A method is also added to
`Iterator` to return the stats:
Stats() influxql.IteratorStats
The remote iterators will also emit their stats in the point
stream upon first connection, on a given interval, and then
finally once the last point has been sent.
Slices of tsm1.Value interfaces are only ever used with all the same
types, and the previous code would switch on the type returned from a
call to Value(), which allocated and returned an interface{} object for
the underlying value.
This change instead type-switches on the tsm1.Value object itself,
allowing it direct access to the underlying value field, eliminating the
unecessary allocations.
There was a fix in 5b1791, but is not present in the current branch likely due to a rebase issue.
The current code panics with a query like:
select value from cpu group by host order by time desc limit 1
This fixes the panic as well as prevents #5193 from re-occurring. The issue is that agressively
closing the cursors clears out the seeks slice so re-seeking will fail.
Ben Johnson
Jonathan A. Sternberg
Joe LeGasse
Jason Wilder