Add a JNI wrapper for reusable distinct hash join - #22392
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Closing for now, may revisit in the future. |
Signed-off-by: Rishi Chandra <rishic@nvidia.com>
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WalkthroughChangesThis change adds a reusable Distinct hash join support
Estimated code review effort: 3 (Moderate) | ~25 minutes Merge Risk: 🟡 Moderate · up to The new reusable join API can crash the process or cause native memory corruption if a join is closed while another thread is probing it. Merge should wait for synchronized lifetime handling or explicit owner acceptance of the concurrent-use restriction. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Description checkExplanation The description accurately explains the reusable distinct build-side hash join, its reuse across probe tables, its relationship to the non-distinct implementation, and the test and documentation coverage. ✨ Finishing Touches🧪 Generate unit tests (beta)
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In `@java/src/main/java/ai/rapids/cudf/Table.java`:
- Around line 3283-3305: Rename the DistinctHashJoin overload
innerJoinGatherMaps to innerDistinctJoinGatherMaps, preserving its existing
validation and gather-map construction behavior and aligning it with the
existing innerDistinctHashJoinGatherMaps and leftDistinctJoinGatherMap naming.
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📒 Files selected for processing (8)
java/src/main/java/ai/rapids/cudf/DistinctHashJoin.javajava/src/main/java/ai/rapids/cudf/MemoryCleaner.javajava/src/main/java/ai/rapids/cudf/Table.javajava/src/main/native/CMakeLists.txtjava/src/main/native/src/DistinctHashJoinJni.cppjava/src/main/native/src/TableJni.cppjava/src/test/java/ai/rapids/cudf/DistinctHashJoinTest.javajava/src/test/java/ai/rapids/cudf/TableTest.java
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rishic3
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/ok to test 50b7a63 |
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/ok to test 8a79eeb |
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| private final DistinctHashJoinCleaner cleaner; | ||
| private final boolean compareNulls; |
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Nit: I know that this naming mirrors what we have in cudf. But the name is objectively clumsy and vague imprecise.
This should read compareNullsEqual.
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Agree that this is a better name and matches the native function parameter name in Table.java. We would also need to rename the public getCompareNulls accessor… Just note that this will introduce yet another inconsistency with HashJoin, which can then be cleaned up in a follow-up.
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Indeed, I've changed this. The libcudf naming is arguably acceptable since in their case it is an enum that is EQUAL or UNEQUAL. I've scoped the analogous change in HashJoin to #23938.
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| /** | ||
| * Computes a gather map that can be used to manifest the result of a left equi-join between | ||
| * two tables where the right table is guaranteed to not contain any duplicated join keys. |
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Nit: Split infinitive.
| * two tables where the right table is guaranteed to not contain any duplicated join keys. | |
| * two tables where the right table is guaranteed not to contain any duplicated join keys. |
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Also in the innerJoinGatherMaps Javadoc.
[Optional] There are some instances in existing functions as well, which we can defer to a follow-up…
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That was a fun wikipedia page.
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"Remember to never split an infinitive"1 😁
Footnotes
| * @param rightHash hash table built from distinct join key columns from the right table | ||
| * @return right table gather map | ||
| */ | ||
| public GatherMap leftJoinGatherMap(DistinctHashJoin rightHash) { |
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I might have lost the plot: Why isn't this function named leftDistinctJoinGatherMap or leftDistinctHashJoinGatherMap?
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@mythrocks beat me to it, so re-anchoring my pending comment here.
[Optional] I see that it's been discussed in #22392 (comment), but just wondering why you chose to go with leftJoinGatherMap and not overload leftDistinctJoinGatherMap? Same question for innerJoinGatherMaps (vs overloading innerDistinctJoinGatherMaps)… It seems that the "distinct" part is important to the API, and the new leftJoinGatherMap name is easy to confuse with leftJoinGatherMaps, while the return types are different. Besides, the native methods do have "distinct" in the name…
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Fixed now, that was an oversight. I failed to see the ongoing pattern.
mythrocks
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mythrocks
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LGTM, barring some trivial nits.
| private static native long[] leftDistinctJoinGatherMap(long leftKeys, long rightKeys, | ||
| boolean compareNullsEqual) throws CudfException; | ||
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| private static native long[] leftDistinctHashJoinGatherMap(long leftTable, |
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[Really optional] Almost certainly a follow-up item: the grouping you have makes sense to me (put distinct method next to another distinct one, given that they both construct a single map), but the rest of the file does not follow this pattern. At some point we'd want to move the non-distinct hash join methods next to the non-distinct regular join methods (i.e., leftJoinGatherMaps above). The same applies to the inner join method ordering…
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Leaving this unchanged for now.
| { | ||
| cudf::jni::auto_set_device(env); | ||
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| auto const build_keys = reinterpret_cast<cudf::table_view const*>(j_build_keys); |
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I'm noticing some asymmetry between these methods and the non-distinct ones in https://github.com/NVIDIA/cudf/blob/main/java/src/main/native/src/HashJoinJni.cpp, namely extra blank lines, local variable naming, the use of make_unique, the absence of the explicit load factor, and the null check in destroy. I don't have a specific preference on which way they should agree (probably a combination of both), but having such superficial differences in what are essentially the same code is often a maintainability burden. Should we plan to bring them in sync, either here or in a follow-up?
| protected synchronized boolean cleanImpl(boolean logErrorIfNotClean) { | ||
| long origAddress = nativeHandle; | ||
| boolean neededCleanup = nativeHandle != 0; | ||
| if (neededCleanup) { |
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[Optional] I'm a big fan of guard clauses, e.g.:
boolean neededCleanup = nativeHandle != 0;
if (!neededCleanup) { return false; }
long origAddress = nativeHandle;
try { destroy(nativeHandle); … } finally { nativeHandle = 0; }
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return true;(up to you whether to keep neededCleanup as an explaining variable or inline it)… Also, a nit: origAddress is only used when neededCleanup is true, so should move into that part of the code.
[Really optional] Also applies to what is essentially identical code in HashJoin.java… Even if we decide to apply the above, feel free to keep them in sync for now and defer both to a follow-up.
| return compareNulls; | ||
| } | ||
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| long getNativeView() { |
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[Really optional] Again, flagging the asymmetry with java/src/main/java/ai/rapids/cudf/HashJoin.java, where this method sits above getNumberOfColumns. FWIW, the ordering here makes more sense to me, so let's plan to clean the other file (including the typo in the getNumberOfColumns Javadoc that you've fixed here) in a follow-up?
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| /** Get the number of join key columns for the table used to generate the hash table. */ | ||
| public long getNumberOfColumns() { | ||
| return cleaner.buildKeys.getNumberOfColumns(); |
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[Optional] Careful: accessing buildKeys without a guard will produce an NPE if invoked after close(), meaning that invoking Table.leftJoinGatherMap with a closed rightHash would also fail with an NPE. Ideally, we'd have explicit "isClosed" guards that throw IllegalStateExceptions.
Also pre-existing in other join classes, so probably worth a larger-scale follow-up.
| * @param rightHash hash table built from distinct join key columns from the right table | ||
| * @return right table gather map | ||
| */ | ||
| public GatherMap leftJoinGatherMap(DistinctHashJoin rightHash) { |
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@mythrocks beat me to it, so re-anchoring my pending comment here.
[Optional] I see that it's been discussed in #22392 (comment), but just wondering why you chose to go with leftJoinGatherMap and not overload leftDistinctJoinGatherMap? Same question for innerJoinGatherMaps (vs overloading innerDistinctJoinGatherMaps)… It seems that the "distinct" part is important to the API, and the new leftJoinGatherMap name is easy to confuse with leftJoinGatherMaps, while the return types are different. Besides, the native methods do have "distinct" in the name…
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| private final DistinctHashJoinCleaner cleaner; | ||
| private final boolean compareNulls; |
There was a problem hiding this comment.
Agree that this is a better name and matches the native function parameter name in Table.java. We would also need to rename the public getCompareNulls accessor… Just note that this will introduce yet another inconsistency with HashJoin, which can then be cleaned up in a follow-up.
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| /** | ||
| * Computes a gather map that can be used to manifest the result of a left equi-join between | ||
| * two tables where the right table is guaranteed to not contain any duplicated join keys. |
There was a problem hiding this comment.
Also in the innerJoinGatherMaps Javadoc.
[Optional] There are some instances in existing functions as well, which we can defer to a follow-up…
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/ok to test 2bf7a6f |
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/ok to test 5b12e29 |
igorpeshansky
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igorpeshansky
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LGTM 
aside from a couple of minor changes (test rename and helper function sync) that belong in this PR. The rest just need appropriate homes in follow-up issues.
| public GatherMap leftJoinGatherMap(DistinctHashJoin rightHash) { | ||
| if (getNumberOfColumns() != rightHash.getNumberOfColumns()) { | ||
| throw new IllegalArgumentException("Column count mismatch, this: " + getNumberOfColumns() + | ||
| "rightKeys: " + rightHash.getNumberOfColumns()); |
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Fair, though confusing. We could do a follow-up pass changing them all to just " right: "… Should we fold it into the #23938 "consistency" issue, or open a new one?
| * @return right table gather map | ||
| */ | ||
| public GatherMap leftJoinGatherMap(DistinctHashJoin rightHash) { | ||
| if (getNumberOfColumns() != rightHash.getNumberOfColumns()) { |
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Well, it's already a problem in that an untested guard can regress. But I'm definitely ok with treating it out of scope for this PR. Should we fold it into the #23939 "hardening" issue, or open a new one?
| public class DistinctHashJoinTest { | ||
| @Test | ||
| void testGetNumberOfColumns() { | ||
| try (Table buildTable = new Table.TestBuilder() |
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Up to you. I'd keep them consistent in the future, though, one way or another — maybe as part of #23938?
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| @Test | ||
| void testGetCompareNulls() { | ||
| try (Table buildTable = new Table.TestBuilder().column(1, 2, 3, 4).build()) { |
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Sorry, I was implying that if the discrepancy is not significant, there's no reason to diverge. If you feel one column is enough, maybe fold into the #23938 "consistency" issue?
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| @Test | ||
| void testLeftJoinGatherMapCanBeReusedAcrossProbeTables() { |
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Across probe tables? 🤔 TableTest.checkInnerDistinctJoin constructs a fresh DistinctHashJoin on each call and probes it exactly once, so innerDistinctJoinGatherMaps(DistinctHashJoin) is covered but never actually reused — and reuse across probes is the whole point of the wrapper. This test only reuses left_join, which is a different libcudf entrypoint from inner_join.
Note that, unlike left_join, the inner_join tests treat the order as unspecified and use a sort (e.g., TableTest.verifyJoinGatherMaps), so I assume the order is not guaranteed and that we can't reuse assertGatherMapEquals to implement the new test…
Not going to block approval on that, though — we could add it in a follow-up, maybe as part of the "hardening" work in #23939 or another hardening issue.
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| } | ||
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| private static void assertGatherMapEquals(ColumnView expected, GatherMap gatherMap) { |
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Sure. Can we at least give it the same name and reorder the parameters, to make later cleanup easier?
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| /** | ||
| * Computes a gather map that can be used to manifest the result of a left equi-join between | ||
| * two tables where the right table is guaranteed to not contain any duplicated join keys. |
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"Remember to never split an infinitive"1 😁
Footnotes
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Should we rename this to testLeftDistinctJoinGatherMapCanBeReusedAcrossProbeTables?
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This fell through the cracks in the API rename… Test names are not significant in themselves, but consistency helps (e.g., for recognizing at a glance which API failed when the test fails)…
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Thanks this makes sense. Added this to #23960.
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/merge |
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Description
Contributes to NVIDIA/cudf-spark#14680.
This adds a JNI wrapper over a distinct build side join table so that it can be reused against a series of probe tables. This essentially mirrors what was done in the non-distinct case #9080, except without the row count APIs. In the distinct inner/left cases the output rows are trivially bounded by the probe rows so there is no real need for computing row counts for sizing.
Checklist