This commit fixes the `MaxSelectSeriesN` limit which was broken by
the implementation of lazy iterators. The setting previously limited
the total number of series but the new implementation limits the
concurrent number of series being processed.
The `SHOW MEASUREMENTS` and `SHOW TAG VALUES` cannot go through the
query engine to get the speed they need. They also only need access to
the database index and do not need access to specific shards. This
removes the query rewriting that was done to turn these two queries into
a select statement and reimplements them inside of the coordinator as an
interface on the TSDBStore.
This commit optimizes `SHOW TAG VALUES` so that it avoids the
`SELECT` query engine execution and iterator creation. There
are also optimizations to reduce individual memory allocations
and to reduce in-memory heap size by only operating on one
measurement at a time.
Execution time has been reduce to approximately 900ms for
500,000 rows. This is about 2µs per row. Of this time,
approximately 1µs is spent retrieving and sorting the row
and 1µs is spent encoding into JSON and writing to the
response body.
For restoring a shard, we need to be able to have the shard open,
but disabled. It was racy to open it and then disable it separately
since writes/queries could occur in between that time.
This allows us to add additional options to ExecuteQuery without
creating parameter bloat.
Removing the unused Series structs. Their necessity was removed by a
previous commit, but the structs were not removed yet.
Add another type of interrupt iterator that monitors the interrupt
channel and calls `Close()` on the iterator when the interrupt happens.
It will primarily be used for asynchronously closing the ReaderIterator,
but it will only close the read side of the connection properly. More
work needs to be done to allow closing the write side efficiently.
Casting syntax is done with the PostgreSQL syntax `field1::float` to
specify which type should be used when selecting a field. You can also
do `field1::field` or `tag1::tag` to specify that a field or tag should
be selected.
This makes it possible to select a tag when a field key and a tag key
conflict with each other in a measurement. It also means it's possible
to choose a field with a specific type if multiple shards disagree. If
no types are given, the same ordering for how a type is chosen is used
to determine which type to return.
The FieldDimensions method has been updated to return the data type for
the fields that get returned. The SeriesKeys function has also been
removed since it is no longer needed. SeriesKeys was originally used for
the fill iterator, but then expanded to be used by auxiliary iterators
for determining the channel iterator types. The fill iterator doesn't
need it anymore and the auxiliary types are better served by
FieldDimensions implementing that functionality, so SeriesKeys is no
longer needed.
Fixes#6519.
Ben Johnson
Jonathan A. Sternberg
Jason Wilder