* initial commits for finalizeFieldAccess #2433
* fix some bugs to run a query
* change name of method Queries.verifyAggregations to Queries.prepareAggregations
* add Uts
* fix Ut failures
* rebased to master
* address comments and add a Ut for arithmetic post aggregators
* rebased to the master
* address the comment of injection within arithmetic post aggregator
* address comments and introduce decorate() in the PostAggregator interface.
* Address comments. 1. Implements getComparator in FinalizingFieldAccessPostAggregator and add Uts for it 2. Some minor changes like renaming a method name.
* Fix a code style mismatch.
* Rebased to the master
* Removing Integer.MAX column size limit.
* On demand creation of headerLong, use v2 instead of v3
* Avoid reusing the same object from a previous test.
* Avoid reusing the same object from a previous test part#2
* code formatting.
* GenericIndexed/Writer code review changes.
* GenericIndexed/writer code review requested changes.
* checkIndex() to static
* native endianess for genericIndexedV2, code review requested changes.
* Formatting
* Hll fix.
* use native endianess during bag size calculation.
* Code review requested changes.
* IOPeon close() changes.
* use different tmp directory path for testing.
* Code review requested changes.
* Less use of File.deleteOnExit()
* removed deleteOnExit from most of the tests/benchmarks/iopeon
* Made IOpeon closable
* Formatting.
* Revert DeterminePartitionsJobTest, remove cleanup method from IOPeon
* Close all aggregators when closing onHeapIncrementalIndex
* Aggregators are now handled as Closeables, remove unnecessary mock in test
* Fix variable shadowing
* Add PostAggregators to generator cache keys for top-n queries
* Add tests for strings
* Remove debug comments
* Add type keys and list sizes to cache key
* Make post aggregators used for sort are considered for cache key generation
* Use assertArrayEquals()
* Improve findPostAggregatorsForSort()
* Address comments
* fix test failure
* address comments
* Simplify LikeFilter implementation of getBitmapIndex, estimateSelectivity.
LikeFilter:
- Reduce code duplication, and simplify methods, at the cost of incurring an extra box
of ImmutableBitmap into a SingletonImmutableList. I think this is fine, since this
should be cheap and the code path is not hot (just once per filter).
Filters:
- Make estimateSelectivity public since it seems intended that they be used by Filter
implementations, and Filters from extensions may want to use them too. Removed
@VisibleForTesting for the same reason.
- Rename one of the estimatePredicateSelectivity overloads to estimateSelectivity, since
predicates aren't involved.
* Address PR comments.
* Remove unused import
* Change List to Collection
* Add filter selectivity estimation for auto search strategy
* Addressed comments
* Lazy bitmap materialization for bitmap sampling and java docs
* Addressed comments.
- Fix wrong non-overlap ratio computation and added unit tests.
- Change Iterable<Integer> to IntIterable
- Remove unnecessary Iterable<Integer>
* Addressed comments
- Split a long ternary operation into if-else blocks
- Add IntListUtils.fromTo()
* Fix test failure and add a test for RangeIntList
* fix code style
* Diabled selectivity estimation for multi-valued dimensions
* Address comment
* Introduce SegmentizerFactory
- that knows how to deserialize specific type of segment
- Default implementation is MMappedQueryableSegmentizerFactory which creates QueryableIndexSegment
- Unit test for the default behavior
* review comments
* Add virtual column types, holder serde, and safety features.
Virtual columns:
- add long, float, dimension selectors
- put cache IDs in VirtualColumnCacheHelper
- adjust serde so VirtualColumns can be the holder object for Jackson
- add fail-fast validation for cycle detection and duplicates
- add expression virtual column in core
Storage adapters:
- move virtual column hooks before checking base columns, to prevent surprises
when a new base column is added that happens to have the same name as a
virtual column.
* Fix ExtractionDimensionSpecs with virtual dimensions.
* Fix unused imports.
* CR comments
* Merge one more time, with feeling.
* * Add DimensionSelector.idLookup() and nameLookupPossibleInAdvance() to allow better inspection of features DimensionSelectors supports, and safer code working with DimensionSelectors in BaseTopNAlgorithm, BaseFilteredDimensionSpec, DimensionSelectorUtils;
* Add PredicateFilteringDimensionSelector, to make BaseFilteredDimensionSpec to be able to decorate DimensionSelectors with unknown cardinality;
* Add DimensionSelector.makeValueMatcher() (two kinds) for DimensionSelector-side specifics-aware optimization of ValueMatchers;
* Optimize getRow() in BaseFilteredDimensionSpec's DimensionSelector, StringDimensionIndexer's DimensionSelector and SingleScanTimeDimSelector;
* Use two static singletons, TrueValueMatcher and FalseValueMatcher, instead of BooleanValueMatcher;
* Add NullStringObjectColumnSelector singleton and use it in MapVirtualColumn
* Rename DimensionSelectorUtils.makeNonDictionaryEncodedIndexedIntsBasedValueMatcher to makeNonDictionaryEncodedRowBasedValueMatcher
* Make ArrayBasedIndexedInts constructor private, replace it's usages with of() static factory method
* Cache baseIdLookup in ForwardingFilteredDimensionSelector
* Fix a bug in DimensionSelectorUtils.makeRowBasedValueMatcher(selector, predicate, matchNull)
* Employ precomputed BitSet optimization in DimensionSelector.makeValueMatcher(value, matchNull) when lookupId() is not available, but cardinality is known and lookupName() is available
* Doc fixes
* Addressed comments
* Fix
* Fix
* Adjust javadoc of DimensionSelector.nameLookupPossibleInAdvance() for SingleScanTimeDimSelector
* throw UnsupportedOperationException instead of IAE in BaseTopNAlgorithm
* Removing unused code from io.druid.java.util.common.guava package; fix#3563 (more consistent and paranoiac resource handing in Sequences subsystem); Add Sequences.wrap() for DRY in MetricsEmittingQueryRunner, CPUTimeMetricQueryRunner and SpecificSegmentQueryRunner; Catch MissingSegmentsException in SpecificSegmentQueryRunner's yielder.next() method (follow up on #3617)
* Make Sequences.withEffect() execute the effect if the wrapped sequence throws exception from close()
* Fix strange code in MetricsEmittingQueryRunner
* Add comment on why YieldingSequenceBase is used in Sequences.withEffect()
* Use Closer in OrderedMergeSequence and MergeSequence to close multiple yielders
* streaming version of select query
* use columns instead of dimensions and metrics;prepare for valueVector;remove granularity
* respect query limit within historical
* use constant
* fix thread name corrupted bug when using jetty qtp thread rather than processing thread while working with SpecificSegmentQueryRunner
* add some test for scan query
* add scan query document
* fix merge conflicts
* add compactedList resultFormat, this format is better for json ser/der
* respect query timeout
* respect query limit on broker
* use static consts and remove unused code
* SQL support for nested groupBys.
Allows, for example, doing exact count distinct by writing:
SELECT COUNT(*) FROM (SELECT DISTINCT col FROM druid.foo)
Contrast with approximate count distinct, which is:
SELECT COUNT(DISTINCT col) FROM druid.foo
* Add deeply-nested groupBy docs, tests, and maxQueryCount config.
* Extract magic constants into statics.
* Rework rules to put preconditions in the "matches" method.
* Add an option to SearchQuery to choose a search query execution strategy.
Supported strategies are
1) Index-only query execution
2) Cursor-based scan
3) Auto: choose an efficient strategy for a given query
* Add SearchStrategy and SearchQueryExecutor
* Address comments
* Rename strategies and set UseIndexesStrategy as the default strategy
* Add a cost-based planner for auto strategy
* Add document
* Fix code style
* apply code style
* apply comments
* Filters: Use ColumnSelectorFactory directly for building row-based matchers.
* Adjustments based on code review.
- BoundDimFilter: fewer volatiles, rename matchesAnything to !matchesNothing.
- HavingSpecs: Clarify that they are not thread-safe, and make DimFilterHavingSpec
not thread safe.
- Renamed rowType to rowSignature.
- Added specializations for time-based vs non-time-based DimensionSelector in RBCSF.
- Added convenience method DimensionHanderUtils.createColumnSelectorPlus.
- Added singleton ZeroIndexedInts.
- Added test cases for DimFilterHavingSpec.
* Make ValueMatcherColumnSelectorStrategy actually use the associated selector.
* Add RangeIndexedInts.
* DimFilterHavingSpec: Fix concurrent usage guard on jdk7.
* Add assertion to ZeroIndexedInts.
* Rename no-longer-volatile members.
* add first and last aggregator
* add test and fix
* moving around
* separate aggregator valueType
* address PR comment
* add finalize inner query and adjust v1 inner indexing
* better test and fixes
* java-util import fixes
* PR comments
* Add first/last aggs to ITWikipediaQueryTest
* GroupByBenchmark: Add serde, spilling, all-gran benchmarks.
Also use more iterations.
* groupBy v2: Ignore timestamp completely when granularity = all, except for the final merge.
Specifically:
- Remove timestamp from RowBasedKey when not needed
- Set timestamp to null in MapBasedRows that are not part of the final merge.
* sortByDimsFirst flag for groupBy query
* Remove need for KeyType in Grouper<KeyType> to be Comparable<KeyType>
* fix review comments
* fix review comments regarding removing code duplication of dim/time comparison
* move comparator for KeyType object to KeySerdeFactory so that creation of comparator does not need KeySerde
* remove unnecessary system.out.println
* make access static var NATURAL_NULLS_FIRST directly
* further review comments addressing
* More robust Filter tests.
All Filter tests now exercise the CNF and post-filtering features.
* Fixes to RowBasedValueMatcherFactory and to bound filters.
- Change Comparables to Strings in ValueMatcher related code.
- Break out RowBasedValueMatcherFactory, fix a variety of issues around nulls, and add tests.
- Fix bound filters on long columns with non-numeric bounds, and add tests.
v1 subqueries try to use aggregators to "transfer" values from the inner
results to an incremental index, but aggregators can't transfer all kinds of
values (strings are a common one). This is a workaround that selectively
ignores what the outer aggregators ask for and instead assumes that we know
best.
These are in the same commit because the name validation changed the kinds of
errors that were thrown by v1 subqueries.
This also involved some other test changes:
- Added a factory.mergeRunners step to AggregationTestHelper's groupBy chain, since the v2
engine does merging there.
- Changed test byteBuffer pools from on-heap to off-heap to work around
https://github.com/DataSketches/sketches-core/pull/116 for datasketches tests.
* Update emitter dependency to 0.4.0 and emit "version" dimension for all druid metrics, not only query metrics
* Remove unused imports
* Use empty string instead of "testing-version" as a version placeholder
Excludes tests from AvoidStaticImport, since those are used often there and
I didn't want to make this changeset too large. Production code use was minimal
and I switched those to non-static imports.
* Add "like" filter.
* Addressed some PR comments.
* Slight simplifications to LikeFilter.
* Additional simplifications.
* Fix comment in LikeFilter.
* Clarify comment in LikeFilter.
* Simplify LikeMatcher a bit.
* No use going through the optimized path if prefix is empty.
* Add more tests.
* Support string type in math expression
addressed comments
addressed comments
Addressed comments
* Updated math function document
* Addressed comments
* Remove unused ComplexColumnImpl class
* Remove throws IOException from close() in GenericColumn, ComplexColumn, IndexedFloats and IndexedLongs
* Use concise try-with-resources syntax in several places
* Fix resource leaks (ComplexColumn and GenericColumn) in SegmentAnalyzer, SearchQueryRunner, QueryableIndexIndexableAdapter and QueryableIndexStorageAdapter
* Use Closer in Iterable, returned from QueryableIndexIndexableAdapter.getRows(), in order to try to close everything even if closing some parts thew exceptions
* Supports expression-paramed aggregator (squashed and rebased on master) also includes math post aggregator (was #2820)
* Addressed comments
* addressed comments
* Remove unused numProcessed param from PooledTopNAlgorithm.aggregateDimValue()
* Replace AtomicInteger with simple int in PooledTopNAlgorithm.scanAndAggregate() and aggregateDimValue()
* Remove unused import
Despite the non-thread-safety of HyperLogLogCollector, it is actually currently used
by multiple threads during realtime indexing. HyperUniquesAggregator's "aggregate" and
"get" methods can be called simultaneously by OnheapIncrementalIndex, since its
"doAggregate" and "getMetricObjectValue" methods are not synchronized.
This means that the optimization of HyperLogLogCollector.fold in #3314 (saving and
restoring position rather than duplicating the storage buffer of the right-hand side)
could cause corruption in the face of concurrent writes.
This patch works around the issue by duplicating the storage buffer in "get" before
returning a collector. The returned collector still shares data with the original one,
but the situation is no worse than before #3314. In the future we may want to consider
making a thread safe version of HLLC that avoids these kinds of problems in realtime
indexing. But for now I thought it was best to do a small change that restored the old
behavior.
* Improve performance of StringDimensionMergerV9 and StringDimensionMergerLegacy by avoiding primitive int boxing by using IntIterator in IndexedInts instead of Iterator<Integer>; Extract some common logic for V9 and Legacy mergers; Minor improvements to resource handling in StringDimensionMergerV9
* Don't mask index in MergeIntIterator.makeQueueElement()
* DRY conversion RoaringBitmap's IntIterator to fastutil's IntIterator
* Do implement skip(n) in IntIterators extending AbstractIntIterator because original implementation is not reliable
* Use Test(expected=Exception.class) instead of try { } catch (Exception e) { /* ignore */ }
- Fix GroupByRowProcessor config overrides
- Fix GroupByRowProcessor resource limit checking
- Invert subquery context overrides such that for the subquery, its own
keys override keys from the outer query, not the other way around.
The last bit is necessary for the test to work, and seems like a better
way to do it anyway.
* Show candidate hosts for the given query
* Added test cases & minor changes to address comments
* Changed path-param to query-pram for intervals/numCandidates
* support renaming of outputName for cached select and search queries
* rebase and resolve conflicts
* rollback CacheStrategy interface change
* updated based on review comments
In ConcurrentGrouper, when it becomes clear that disk spilling is necessary, switch
from hash-based partitioning to thread-based partitioning. This stops processing
threads from blocking each other while spilling is occurring.
Also change defaults:
- bufferGrouperMaxLoadFactor from 0.75 to 0.7.
- maxMergingDictionarySize to 100MB from 25MB, should be more appropriate
for most heaps.
* Eager file unmapping in IndexIO, IndexMerger and IndexMergerV9. The exact purpose for this change is to allow running IndexMergeBenchmark in Windows, however should also be universally 'better' than non-deterministic unmapping, done when MappedByteBuffers are garbage-collected (BACKEND-312)
* Use Closer with a proper pattern in IndexIO, IndexMerger and IndexMergerV9
* Unmap file in IndexMergerV9.makeInvertedIndexes() using try-with-resources
* Reformat IndexIO
FilterOutputStream has an inefficient implementation of write(byte[], int, int).
So let's extend OutputStream directly and use efficient implementations of all
methods.
The old TopNFunction code did Sequences.toList on the input sequence before
using a priority queue to find the top N items. Now, the priority queue
is used in an accumulator, so there is no need to fully materialize the results.
Also removed equals/hashCode from the limitFn and remove limitFn from the
GroupByQuery's hashCode, since that wasn't necessary and the implementation
of hashCode wasn't correct anyway.
* support query granularity and interval for search query
* skip unncessary bitmap calculation when query interval contains whole the data interval of the given segments.
* use binary search to find start and end index for the given interval
* fix based on comment
* bug fix based on the review comments and add unit tests
Without this transformation, distribution of hash % X is poor in general.
It is catastrophically poor when X is a multiple of 31 (many slots would
be empty).
* introducing lists of existing columns in the fields of select queries' output
* rebase master
* address the comment. add test code for select query caching
* change the cache code in SelectQueryQueryToolChest to 0x16
Follow-up to #1773, which meant to add more useful query errors but
did not actually do so. Since that patch, any error other than
interrupt/cancel/timeout was reported as `{"error":"Unknown exception"}`.
With this patch, the error fields are:
- error, one of the specific strings "Query interrupted", "Query timeout",
"Query cancelled", or "Unknown exception" (same behavior as before).
- errorMessage, the message of the topmost non-QueryInterruptedException
in the causality chain.
- errorClass, the class of the topmost non-QueryInterruptedException
in the causality chain.
- host, the host that failed the query.
1. Wrap temporaryStorage in a resource holder, to avoid spurious "Closed"
errors from already-running processing tasks.
2. Exit early from the merging accumulator if the query is cancelled.
* Add time interval dim filter and retention analysis example
* Use closed-open matching for intervals, update cache key generation
* Fix time filtering tests for interval boundary change
- HLLC.fold avoids duplicating the other buffer by saving and restoring its position.
- HLLC.makeCollector(buffer) no longer duplicates incoming BBs.
- Updated call sites where appropriate to duplicate BBs passed to HLLC.
The common theme between the two is they both create "fake" DimensionSelectors
that work on top of Rows. They both do it because there isn't really any
dictionary for the underlying Rows, they're just a stream of data. The fix for
both is to allow a DimensionSelector to tell callers that it has no dictionary
by returning CARDINALITY_UNKNOWN from getValueCardinality. The callers, in
turn, can avoid using it in ways that assume it has a dictionary.
Fixes#3311.
Add tests for the CCE and for a bunch of other groupBy stuff.
Also avoids setting the interrupted flag when InterruptedExceptions
happen, since this might interfere with resource closing, no other
query does it, and is probably pointless anyway since the thread
is likely to be a jetty thread that we don't actually want to set
an interrupt flag on.
Also fixes toString on OrderByColumnSpec.
* ability to not rollup at index time, make pre aggregation an option
* rename getRowIndexForRollup to getPriorIndex
* fix doc misspelling
* test query using no-rollup indexes
* fix benchmark fail due to jmh bug
* Add numeric StringComparator
* Only use direct long comparison for numeric ordering in BoundFilter, add time filtering benchmark query
* Address PR comments, add multithreaded BoundDimFilter test
* Add comment on strlen tie handling
* Add timeseries interval filter benchmark
* Adjust docs
* Use jackson for StringComparator, address PR comments
* Add new TopNMetricSpec and SearchSortSpec with tests (WIP)
* More TopNMetricSpec and SearchSortSpec tests
* Fix NewSearchSortSpec serde
* Update docs for new DimensionTopNMetricSpec
* Delete NumericDimensionTopNMetricSpec
* Delete old SearchSortSpec
* Rename NewSearchSortSpec to SearchSortSpec
* Add TopN numeric comparator benchmark, address PR comments
* Refactor OrderByColumnSpec
* Add null checks to NumericComparator and String->BigDecimal conversion function
* Add more OrderByColumnSpec serde tests
This fixes a potential issue where groupBy resources could be allocated to
create a Sequence, but then the Sequence is never used, and thus the resources
are never freed.
Also simplifies how groupBy handles config overrides (this made the new
unit test easier to write).
Refcounting prevents releasing the merge buffer, or closing the concurrent
grouper, before the processing threads have all finished. The better
error handling prevents an avalanche of per-runner exceptions when grouping
resources are exhausted, by grouping those all up into a single merged
exception.
* Support filtering on __time column
* Rename DruidPredicate
* Add docs for ValueMatcherFactory, add comment on getColumnCapabilities
* Combine ValueMatcherFactory predicate methods to accept DruidCompositePredicate
* Address PR comments (support filter on all long columns)
* Use predicate factory instead of composite predicate
* Address PR comments
* Lazily initialize long handling in selector/in filter
* Move long value parsing from InFilter to InDimFilter, make long value parsing thread-safe
* Add multithreaded selector/in filter test
* Fix non-final lock object in SelectorDimFilter
Fixes inconsistent metric handling between the two implementations. Formerly,
RealtimePlumber only emitted query/segmentAndCache/time and query/wait and
Appenderator only emitted query/partial/time and query/wait (all per sink).
Now they both do the same thing:
- query/segmentAndCache/time, query/segment/time are the time spent per sink.
- query/cpu/time is the CPU time spent per query.
- query/wait/time is the executor waiting time per sink.
These generally match historical metrics, except segmentAndCache & segment
mean the same thing here, because one Sink may be partially cached and
partially uncached and we aren't splitting that out.
constantly timing out on one of slow build machines, increasing the
timeout fixed it.
Running io.druid.granularity.QueryGranularityTest
Tests run: 33, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 11.776
sec - in io.druid.granularity.QueryGranularityTest
All query metrics now start with toolChest.makeMetricBuilder, and all of
*those* now start with DruidMetrics.makePartialQueryTimeMetric. Also, "id"
moved to common code, since all query metrics added it anyway.
In particular this will add query-type specific dimensions like "threshold"
and "numDimensions" to servlet-originated metrics like query/time.
This is actually reasonable for a groupBy or lexicographic topNs that is
being used to do a "COUNT DISTINCT" kind of query. No aggregators are
needed for that query, and including a dummy aggregator wastes 8 bytes
per row.
It's kind of silly for timeseries, but why not.
* support alphanumeric sort in search query
* address a comment about handling equals() and hashCode()
* address comments
* add Ut for string comparators
* address a comment about space indentations.
This patch introduces a GroupByStrategy concept and two strategies: "v1"
is the current groupBy strategy and "v2" is a new one. It also introduces
a merge buffers concept in DruidProcessingModule, to try to better
manage memory used for merging.
Both of these are described in more detail in #2987.
There are two goals of this patch:
1. Make it possible for historical/realtime nodes to return larger groupBy
result sets, faster, with better memory management.
2. Make it possible for brokers to merge streams when there are no order-by
columns, avoiding materialization.
This patch does not do anything to help with memory management on the broker
when there are order-by columns or when there are nested queries. That could
potentially be done in a future patch.
* add get dimension rangeset to filters
* add get domain to ShardSpec and added chunk filter in caching clustered client
* add null check and modified not filter, started with unit test
* add filter test with caching
* refactor and some comments
* extract filtershard to helper function
* fixup
* minor changes
* update javadoc
* fix caching for search results
properly read count when reading from cache.
* fix NPE during merging search count and add test
* Update cache key to invalidate prev results
* Add lookup optimization for InDimFilter
* tests for in filter with lookup extraction fn
* refactor
* refactor2 and modified filter test
* make optimizeLookup private
* Allows RegisteredLookupExtractionFn to find its lookups lazily
* Use raw variables instead of AtomicReference
* Make sure to use volatile
* Remove extra local variable.
* Move from BAOS to ByteBuffer
* Optimize filter for timeseries, search, and select queries
* exception at failed toolchest type check
* took out query type check
* java7 error fix and test improvement
* Fix parsing fail of segment id with underscored datasource (Fix for #2786)
* addressed comment
* renamed and moved code into api. added log4 dependency for tests
* addressed comments
* fixed test fails
* make isSingleThreaded groupBy query processing overridable at query time
* refactor code in GroupByMergedQueryRunner to make processing of single threaded and parallel merging of runners consistent
* Document how to use roaring bitmaps
This fixes#2408.
While not all indexSpec properties are explained, it does explain how roaring bitmaps can be turned on.
* fix
* fix
* fix
* fix
The behavior is now that filters on "null" will match rows with no
values. The behavior in the past was inconsistent; sometimes these
filters would match and sometimes they wouldn't.
Adds tests for this behavior to SelectorFilterTest and
BoundFilterTest, for query-level filters and filtered aggregates.
Fixes#2750.
BoundFilter:
- For lexicographic bounds, use bitmapIndex.getIndex to find the start and end points,
then union all bitmaps between those points.
- For alphanumeric bounds, iterate through dimValues, and union all bitmaps for values
matching the predicate.
- Change behavior for nulls: it used to be that the BoundFilter would never match nulls,
now it matches nulls if "" is allowed by the lower limit and not excluded by the
upper limit.
Interface changes:
- BitmapIndex: add `int getIndex(value)` to make it possible to get the index for a
value without retrieving the bitmap.
- BitmapIndex: remove `ImmutableBitmap getBitmap(value)`, change callers to `getBitmap(getIndex(value))`.
- BitmapIndexSelector: allow retrieving the underlying BitmapIndex through getBitmapIndex.
- Clarified contract of indexOf in Indexed, GenericIndexed.
Also added tests for SelectorFilter, NotFilter, and BoundFilter.
I believe that the instanceof chain in Filters exists because in the past, Filter
and DimFilter were in different packages (DimFilter was in druid-client and Filter
was in druid-processing). And since druid-client didn't depend on druid-processing,
DimFilter couldn't have a toFilter method. But now it can.
This removes Filter.makeMatcher(ColumnSelectorFactory) and adds a
ValueMatcherFactory implementation to FilteredAggregatorFactory so it can
take advantage of existing makeMatcher(ValueMatcherFactory) implementations.
This patch also removes the Bound-based method from ValueMatcherFactory. Its
only user was the SpatialFilter, which could use the Predicate-based method.
Fixes#2604.
- Add central doc for multi-value dimensions, with some content from other docs.
- Link to multi-value dimension doc from topN and groupBy docs.
- Fixes a broken link from dimensionspecs.md, which was presciently already
linking to this nonexistent doc.
- Resolve inconsistent naming in docs & code (sometimes "multi-valued", sometimes
"multi-value") in favor of "multi-value".
Gian Merlino
Jihoon Son
Jonathan Wei
kaijianding
Akash Dwivedi
DaimonPl
Himanshu
Pierre
Parag Jain
Roman Leventov
Slim
Erik Dubbelboer
Navis Ryu
Keuntae Park
Jisoo Kim
Charles Allen
Dave Li
jaehong choi
rajk-tetration
Nishant
Hyukjin Kwon
michaelschiff
John Wang
Kurt Young
David Lim
binlijin
Xavier Léauté
Fangjin Yang
michaelschiff
Maarten Rijke
Slim Bouguerra
jon-wei
Parag Jain