* Automatic sizing for GroupBy dictionary sizes.
Merging and selector dictionary sizes currently both default to 100MB.
This is not optimal, because it can lead to OOM on small servers and
insufficient resource utilization on larger servers. It also invites
end users to try to tune it when queries run out of dictionary space,
which can make things worse if the end user sets it to too high.
So, this patch:
- Adds automatic tuning for selector and merge dictionaries. Selectors
use up to 15% of the heap and merge buffers use up to 30% of the heap
(aggregate across all queries).
- Updates out-of-memory error messages to emphasize enabling disk
spilling vs. increasing memory parameters. With the memory parameters
automatically sized, it is more likely that an end user will get
benefit from enabling disk spilling.
- Removes the query context parameters that allow lowering of configured
dictionary sizes. These complicate the calculation, and I don't see a
reasonable use case for them.
* Adjust tests.
* Review adjustments.
* Additional comment.
* Remove unused import.
* ConcurrentGrouper: Add option to always slice up merge buffers thread-locally.
Normally, the ConcurrentGrouper shares merge buffers across processing
threads until spilling starts, and then switches to a thread-local model.
This minimizes memory use and reduces likelihood of spilling, which is
good, but it creates thread contention. The new mergeThreadLocal option
causes a query to start in thread-local mode immediately, and allows us
to experiment with the relative performance of the two modes.
* Fix grammar in docs.
* Fix race in ConcurrentGrouper.
* Fix issue with timeouts.
* Remove unused import.
* Add "tradeoff" to dictionary.
* Reduce allocations due to Jackson serialization.
This patch attacks two sources of allocations during Jackson
serialization:
1) ObjectMapper.writeValue and JsonGenerator.writeObject create a new
DefaultSerializerProvider instance for each call. It has lots of
fields and creates pressure on the garbage collector. So, this patch
adds helper functions in JacksonUtils that enable reuse of
SerializerProvider objects and updates various call sites to make
use of this.
2) GroupByQueryToolChest copies the ObjectMapper for every query to
install a special module that supports backwards compatibility with
map-based rows. This isn't needed if resultAsArray is set and
all servers are running Druid 0.16.0 or later. This release was a
while ago. So, this patch disables backwards compatibility by default,
which eliminates the need to copy the heavyweight ObjectMapper. The
patch also introduces a configuration option that allows admins to
explicitly enable backwards compatibility.
* Add test.
* Update additional call sites and add to forbidden APIs.
* GroupBy: Cap dictionary-building selector memory usage.
New context parameter "maxSelectorDictionarySize" controls when the
per-segment processing code should return early and trigger a trip
to the merge buffer.
Includes:
- Vectorized and nonvectorized implementations.
- Adjustments to GroupByQueryRunnerTest to exercise this code in
the v2SmallDictionary suite. (Both the selector dictionary and
the merging dictionary will be small in that suite.)
- Tests for the new config parameter.
* Fix issues from tests.
* Add "pre-existing" to dictionary.
* Simplify GroupByColumnSelectorStrategy interface by removing one of the writeToKeyBuffer methods.
* Adjustments from review comments.
As part of #12078 one of the followup's was to have a specific config which does not allow accidental unnesting of multi value columns if such columns become part of the grouping key.
Added a config groupByEnableMultiValueUnnesting which can be set in the query context.
The default value of groupByEnableMultiValueUnnesting is true, therefore it does not change the current engine behavior.
If groupByEnableMultiValueUnnesting is set to false, the query will fail if it encounters a multi-value column in the grouping key.
* refactor and link fixes
* add sql docs to left nav
* code format for needle
* updated web console script
* link fixes
* update earliest/latest functions
* edits for grammar and style
* more link fixes
* another link
* update with #12226
* update .spelling file
* Remove OffheapIncrementalIndex and clarify aggregator thread-safety needs.
This patch does the following:
- Removes OffheapIncrementalIndex.
- Clarifies that Aggregators are required to be thread safe.
- Clarifies that BufferAggregators and VectorAggregators are not
required to be thread safe.
- Removes thread safety code from some DataSketches aggregators that
had it. (Not all of them did, and that's OK, because it wasn't necessary
anyway.)
- Makes enabling "useOffheap" with groupBy v1 an error.
Rationale for removing the offheap incremental index:
- It is only used in one rare scenario: groupBy v1 (which is non-default)
in "useOffheap" mode (also non-default). So you have to go pretty deep
into the wilderness to get this code to activate in production. It is
never used during ingestion.
- Its existence complicates developer efforts to reason about how
aggregators get used, because the way it uses buffer aggregators is so
different from how every other query engine uses them.
- It doesn't have meaningful testing.
By the way, I do believe that the given way the offheap incremental index
works, it actually didn't require buffer aggregators to be thread-safe.
It synchronizes on "aggregate" and doesn't call "get" until it has
stopped calling "aggregate". Nevertheless, this is a bother to think about,
and for the above reasons I think it makes sense to remove the code anyway.
* Remove things that are now unused.
* Revert removal of getFloat, getLong, getDouble from BufferAggregator.
* OAK-related warnings, suppressions.
* Unused item suppressions.
* First draft of grouping_id function
* Add more tests and documentation
* Add calcite tests
* Fix travis failures
* bit of a change
* Add documentation
* Fix typos
* typo fix
* subtotalsSpec results with null values
Document the format change in results of a groupBy query with a subtotalsSpec. This update applies to 0.18 and later.
* Review catches
* Refresh query docs.
Larger changes:
- New doc: querying/datasource.md describes the various kinds of
datasources you can use, and has examples for both SQL and native.
- New doc: querying/query-execution.md describes how native queries
are executed at a high level. It doesn't go into the details of specific
query engines or how queries run at a per-segment level. But I think it
would be good to add or link that content here in the future.
- Refreshed doc: querying/sql.md updated to refer to joins, reformatted
a bit, added a new "Query translation" section that explains how
queries are translated from SQL to native, and removed configuration
details (moved to configuration/index.md).
- Refreshed doc: querying/joins.md updated to refer to join datasources.
Smaller changes:
- Add helpful banners to the top of query documentation pages telling
people whether a given page describes SQL, native, or both.
- Add SQL metrics to operations/metrics.md.
- Add some color and cross-links in various places.
- Add native query component docs to the sidebar, and renamed them so
they look nicer.
- Remove Select query from the sidebar.
- Fix Broker SQL configs in configuration/index.md. Remove them from
querying/sql.md.
- Combined querying/searchquery.md and querying/searchqueryspec.md.
* Updates.
* Fix numbering.
* Fix glitches.
* Add new words to spellcheck file.
* Assorted changes.
* Further adjustments.
* Add missing punctuation.
* groupBy query: optional limit push down to segment scan
* make segment level limit push down configurable
* fix teamcity errors
* fix segment limit pushdown flag handling on query level config override
* use equals for comparator check
* fix sql and null handling
* fix unused imports
* handle null offset in NullableValueGroupByColumnSelectorStrategy for buffer comparator similar to RowBasedGrouperHelper.NullableRowBasedKeySerdeHelper
Clint Wylie
317brian
Gian Merlino
Gian Merlino
Karan Kumar
Victoria Lim
sthetland
Abhishek Agarwal
Jonathan Wei
Vadim Ogievetsky
Himanshu
Chi Cao Minh