Re: [DISCUSS][Java] Support non-nullable vectors
Hi Wes, Thanks for your good suggestion, we will think about it. Hi Jacques, Thanks for your feedback. Please allow me to address some of your concerns: > This change is undesirable as it optimizes one path and makes several others behave in unintended ways. Could you please elaborate more on this? > What happens if a vector with nulls shows up? What happens if a user sets a position to a null value in user code when this flag set? Please note that in addition to the flag, we also have BaseValueVector#nullable to tell if a vector is nullable. So if BaseValueVector#nullable = true, it is OK to set a null in any position. However, if BaseValueVector#nullable = false and the user tries to set null in some position, there must be some bugs in their code. > If the answer to the above questions is the use is an advanced user, then > why can't they just call: > PlatformDependent.getInt(vector.memoryAddress() + position * 4). > Why would we introduce something directly in the vector class for this > specialized use case? If the user is advanced, that short memory access > invocation seems fine to use. IMO, the problems of directly invoking the PlatformDependent APIs include: 1. The validity buffer for the vector is still allocated anyway, so the benefit of reduced memory consumption is lost. 2. The user can only use this trick in their client code. If they need to use our libraries (e.g. flight, adapter, algorithm), they still have to pay the performance price. 3. If we simply skip the validity buffer and manipulate the data buffer directly, the vector will easily end up in an inconsistent state, causing unexpected problems. > The whole idea with Arrow is that if you have a specialized algorithm, you can hand write memory reads and writes because you have predictable memory layout. This sounds reasonable. IMO, supporting non-nullable vectors is not a specialized requirement. Instead, it is a general requirement, and has a wide range of applications, especially in relational data processing. So it deserves some special treatment (I think), given the benefits discussed above. Please think about it. Best, Liya Fan On Thu, Sep 10, 2020 at 11:32 PM Wes McKinney wrote: > I agree with Jacques here. Perhaps what is needed is an unsafe > non-nullable array accessor layer, then there is no need for flags > etc. We've already been writing a lot of such code in C++ (splitting > between no-nulls and some-nulls paths, see also the BitBlockCounter > stuff we've been doing, is such a thing available in Java yet?) and it > hasn't seemed especially burdensome to me. > > On Thu, Sep 10, 2020 at 9:37 AM Jacques Nadeau wrote: > > > > This change is undesirable as it optimizes one path and makes several > > others behave in unintended ways. What happens if a vector with nulls > > shows up? What happens if a user sets a position to a null value in user > > code when this flag set? > > > > If the answer to the above questions is the use is an advanced user, then > > why can't they just call: > > PlatformDependent.getInt(vector.memoryAddress() + position * 4). > > > > Why would we introduce something directly in the vector class for this > > specialized use case? If the user is advanced, that short memory access > > invocation seems fine to use. The whole idea with Arrow is that if you > have > > a specialized algorithm, you can hand write memory reads and writes > because > > you have predictable memory layout. > > > > On Wed, Sep 9, 2020 at 1:11 AM Fan Liya wrote: > > > > > Hi all, > > > > > > Thanks a lot for your previous feedback. > > > > > > Now we have made some investigation and prepared an initial PR > supporting > > > the non-nullable IntVector [1], as this represents a common scenario. > > > Some initial observations and conclusions can be made. > > > > > > The basic idea of the PR is to provide a global static final flag > > > (NON_NULLABLE_VECTORS_ENABLED) to enable/disable the new feature. > > > 1. When the flag is enabled, manipulations to the validity buffer > would be > > > by-passed if the vector is non-nullable. > > > 2. When the flag is disabled, the behavior is identical to the original > > > code. > > > > > > *First*, we want to show that the change is small. To support the > > > non-nullable IntVector, we need to change classes IntVector, > > > BaseFixedWidthVector (the superclass of IntVector), and BaseValueVector > > > (the superclass of BaseFixedWidthVector). The amount of changes (lines > of > > > code) to each class is given below > > > > > > Class > > > > > > Additions (#lines) > > > > > > Deletions (#lines) > > > > > > Total # lines > > > > > > IntVector > > > > > > 12 > > > > > > 5 > > > > > > 370 > > > > > > BaseFixedWidthVector > > > > > > 30 > > > > > > 11 > > > > > > 925 > > > > > > BaseValueVector > > > > > > 7 > > > > > > 0 > > > > > > 240 > > > > > > It can be seen that the change is small, relative to the class size. > In > > > addition, to support additional vector types, we
Re: [DISCUSS][Java] Support non-nullable vectors
I agree with Jacques here. Perhaps what is needed is an unsafe non-nullable array accessor layer, then there is no need for flags etc. We've already been writing a lot of such code in C++ (splitting between no-nulls and some-nulls paths, see also the BitBlockCounter stuff we've been doing, is such a thing available in Java yet?) and it hasn't seemed especially burdensome to me. On Thu, Sep 10, 2020 at 9:37 AM Jacques Nadeau wrote: > > This change is undesirable as it optimizes one path and makes several > others behave in unintended ways. What happens if a vector with nulls > shows up? What happens if a user sets a position to a null value in user > code when this flag set? > > If the answer to the above questions is the use is an advanced user, then > why can't they just call: > PlatformDependent.getInt(vector.memoryAddress() + position * 4). > > Why would we introduce something directly in the vector class for this > specialized use case? If the user is advanced, that short memory access > invocation seems fine to use. The whole idea with Arrow is that if you have > a specialized algorithm, you can hand write memory reads and writes because > you have predictable memory layout. > > On Wed, Sep 9, 2020 at 1:11 AM Fan Liya wrote: > > > Hi all, > > > > Thanks a lot for your previous feedback. > > > > Now we have made some investigation and prepared an initial PR supporting > > the non-nullable IntVector [1], as this represents a common scenario. > > Some initial observations and conclusions can be made. > > > > The basic idea of the PR is to provide a global static final flag > > (NON_NULLABLE_VECTORS_ENABLED) to enable/disable the new feature. > > 1. When the flag is enabled, manipulations to the validity buffer would be > > by-passed if the vector is non-nullable. > > 2. When the flag is disabled, the behavior is identical to the original > > code. > > > > *First*, we want to show that the change is small. To support the > > non-nullable IntVector, we need to change classes IntVector, > > BaseFixedWidthVector (the superclass of IntVector), and BaseValueVector > > (the superclass of BaseFixedWidthVector). The amount of changes (lines of > > code) to each class is given below > > > > Class > > > > Additions (#lines) > > > > Deletions (#lines) > > > > Total # lines > > > > IntVector > > > > 12 > > > > 5 > > > > 370 > > > > BaseFixedWidthVector > > > > 30 > > > > 11 > > > > 925 > > > > BaseValueVector > > > > 7 > > > > 0 > > > > 240 > > > > It can be seen that the change is small, relative to the class size. In > > addition, to support additional vector types, we only need to change the > > sub-classes, and no more need to change the super classes. > > > > *Second*, we want to show that the performance improvement is notable. To > > see this, we give the performance data of the IntBenchmark (with some > > benchmarks added in the PR). To make the performance as good as possible, > > we enable the ARROW_ENABLE_UNSAFE_MEMORY_ACCESS flag and disable > > the ARROW_ENABLE_NULL_CHECK_FOR_GET flag. Below, we give the data with the > > non-nullable vector flag turned off and on, respectively. > > > > > > > > > > > > > > > > > > *(Vector non-nullable flag off)Benchmark Mode Cnt > > Score Error UnitsIntBenchmarks.getInt avgt5 > > 384.948 ± 3.336 ns/opIntBenchmarks.isNull avgt5 > > 1301.005 ± 54.239 ns/opIntBenchmarks.setIntDirectly avgt5 > > 15387.486 ± 555.749 ns/opIntBenchmarks.setWithValueHolder avgt5 > > 15251.351 ± 134.286 ns/opIntBenchmarks.setWithWriter avgt5 > > 28595.586 ± 932.528 ns/op* > > > > *(Vector non-nullable flag on)* > > > > > > > > > > *IntBenchmarks.getInt avgt5384.630 ±1.547 > > ns/opIntBenchmarks.isNull avgt5 3.004 ±0.110 > > ns/opIntBenchmarks.setIntDirectly avgt5 13511.605 ± 135.455 > > ns/opIntBenchmarks.setWithValueHolder avgt5 13035.883 ± 196.081 > > ns/opIntBenchmarks.setWithWriter avgt5 24734.825 ± 1603.708 > > ns/op* > > > > For the *getInt *operation, there is little performance difference. This > > is because we disable the ARROW_ENABLE_NULL_CHECK_FOR_GET flag, so > > manipulations to the validity buffer are by-passed, even if the > > non-nullable vector flag is off. When the ARROW_ENABLE_NULL_CHECK_FOR_GET > > is enabled, there is a 72.4% performance improvement gained by turning on > > the non-nullable vector flag. > > > > For the isNull operation, we see 3 orders of magnitude performance > > improvements by enabling the non-nullable vector flag. > > > > For other operations, we see 12.2%, 13.5% and 14.5% performance > > improvements by turning on the non-nullable vector flag. > > > > So it can be seen that notable performance improvements can be gained for > > non-nullable vectors. > > > > *Third*, we want to claim that for nullable vectors and scenarios when we > > turn off the
Re: [DISCUSS][Java] Support non-nullable vectors
This change is undesirable as it optimizes one path and makes several others behave in unintended ways. What happens if a vector with nulls shows up? What happens if a user sets a position to a null value in user code when this flag set? If the answer to the above questions is the use is an advanced user, then why can't they just call: PlatformDependent.getInt(vector.memoryAddress() + position * 4). Why would we introduce something directly in the vector class for this specialized use case? If the user is advanced, that short memory access invocation seems fine to use. The whole idea with Arrow is that if you have a specialized algorithm, you can hand write memory reads and writes because you have predictable memory layout. On Wed, Sep 9, 2020 at 1:11 AM Fan Liya wrote: > Hi all, > > Thanks a lot for your previous feedback. > > Now we have made some investigation and prepared an initial PR supporting > the non-nullable IntVector [1], as this represents a common scenario. > Some initial observations and conclusions can be made. > > The basic idea of the PR is to provide a global static final flag > (NON_NULLABLE_VECTORS_ENABLED) to enable/disable the new feature. > 1. When the flag is enabled, manipulations to the validity buffer would be > by-passed if the vector is non-nullable. > 2. When the flag is disabled, the behavior is identical to the original > code. > > *First*, we want to show that the change is small. To support the > non-nullable IntVector, we need to change classes IntVector, > BaseFixedWidthVector (the superclass of IntVector), and BaseValueVector > (the superclass of BaseFixedWidthVector). The amount of changes (lines of > code) to each class is given below > > Class > > Additions (#lines) > > Deletions (#lines) > > Total # lines > > IntVector > > 12 > > 5 > > 370 > > BaseFixedWidthVector > > 30 > > 11 > > 925 > > BaseValueVector > > 7 > > 0 > > 240 > > It can be seen that the change is small, relative to the class size. In > addition, to support additional vector types, we only need to change the > sub-classes, and no more need to change the super classes. > > *Second*, we want to show that the performance improvement is notable. To > see this, we give the performance data of the IntBenchmark (with some > benchmarks added in the PR). To make the performance as good as possible, > we enable the ARROW_ENABLE_UNSAFE_MEMORY_ACCESS flag and disable > the ARROW_ENABLE_NULL_CHECK_FOR_GET flag. Below, we give the data with the > non-nullable vector flag turned off and on, respectively. > > > > > > > > > *(Vector non-nullable flag off)Benchmark Mode Cnt > Score Error UnitsIntBenchmarks.getInt avgt5 > 384.948 ± 3.336 ns/opIntBenchmarks.isNull avgt5 > 1301.005 ± 54.239 ns/opIntBenchmarks.setIntDirectly avgt5 > 15387.486 ± 555.749 ns/opIntBenchmarks.setWithValueHolder avgt5 > 15251.351 ± 134.286 ns/opIntBenchmarks.setWithWriter avgt5 > 28595.586 ± 932.528 ns/op* > > *(Vector non-nullable flag on)* > > > > > *IntBenchmarks.getInt avgt5384.630 ±1.547 > ns/opIntBenchmarks.isNull avgt5 3.004 ±0.110 > ns/opIntBenchmarks.setIntDirectly avgt5 13511.605 ± 135.455 > ns/opIntBenchmarks.setWithValueHolder avgt5 13035.883 ± 196.081 > ns/opIntBenchmarks.setWithWriter avgt5 24734.825 ± 1603.708 > ns/op* > > For the *getInt *operation, there is little performance difference. This > is because we disable the ARROW_ENABLE_NULL_CHECK_FOR_GET flag, so > manipulations to the validity buffer are by-passed, even if the > non-nullable vector flag is off. When the ARROW_ENABLE_NULL_CHECK_FOR_GET > is enabled, there is a 72.4% performance improvement gained by turning on > the non-nullable vector flag. > > For the isNull operation, we see 3 orders of magnitude performance > improvements by enabling the non-nullable vector flag. > > For other operations, we see 12.2%, 13.5% and 14.5% performance > improvements by turning on the non-nullable vector flag. > > So it can be seen that notable performance improvements can be gained for > non-nullable vectors. > > *Third*, we want to claim that for nullable vectors and scenarios when we > turn off the non-nullable vector flag, the new changes do not introduce > performance regression. Such concern is plausible, as our changes add some > if-else branches to the code, which may degrade performance. > > We give the benchmark results of the original code, as below. > > *(original ocde)* > > > > > > *Benchmark Mode Cnt Score Error > UnitsIntBenchmarks.getInt avgt5383.511 ± 0.156 > ns/opIntBenchmarks.isNull avgt5 1274.271 ± 19.092 > ns/opIntBenchmarks.setIntDirectly avgt5 15162.219 ± 194.956 > ns/opIntBenchmarks.setWithValueHolder avgt5 15247.640 ± 153.103 > ns/opIntBenchmarks.setWithWriter
Re: [DISCUSS][Java] Support non-nullable vectors
Hi all, Thanks a lot for your previous feedback. Now we have made some investigation and prepared an initial PR supporting the non-nullable IntVector [1], as this represents a common scenario. Some initial observations and conclusions can be made. The basic idea of the PR is to provide a global static final flag (NON_NULLABLE_VECTORS_ENABLED) to enable/disable the new feature. 1. When the flag is enabled, manipulations to the validity buffer would be by-passed if the vector is non-nullable. 2. When the flag is disabled, the behavior is identical to the original code. *First*, we want to show that the change is small. To support the non-nullable IntVector, we need to change classes IntVector, BaseFixedWidthVector (the superclass of IntVector), and BaseValueVector (the superclass of BaseFixedWidthVector). The amount of changes (lines of code) to each class is given below Class Additions (#lines) Deletions (#lines) Total # lines IntVector 12 5 370 BaseFixedWidthVector 30 11 925 BaseValueVector 7 0 240 It can be seen that the change is small, relative to the class size. In addition, to support additional vector types, we only need to change the sub-classes, and no more need to change the super classes. *Second*, we want to show that the performance improvement is notable. To see this, we give the performance data of the IntBenchmark (with some benchmarks added in the PR). To make the performance as good as possible, we enable the ARROW_ENABLE_UNSAFE_MEMORY_ACCESS flag and disable the ARROW_ENABLE_NULL_CHECK_FOR_GET flag. Below, we give the data with the non-nullable vector flag turned off and on, respectively. *(Vector non-nullable flag off)Benchmark Mode Cnt Score Error UnitsIntBenchmarks.getInt avgt5 384.948 ± 3.336 ns/opIntBenchmarks.isNull avgt5 1301.005 ± 54.239 ns/opIntBenchmarks.setIntDirectly avgt5 15387.486 ± 555.749 ns/opIntBenchmarks.setWithValueHolder avgt5 15251.351 ± 134.286 ns/opIntBenchmarks.setWithWriter avgt5 28595.586 ± 932.528 ns/op* *(Vector non-nullable flag on)* *IntBenchmarks.getInt avgt5384.630 ±1.547 ns/opIntBenchmarks.isNull avgt5 3.004 ±0.110 ns/opIntBenchmarks.setIntDirectly avgt5 13511.605 ± 135.455 ns/opIntBenchmarks.setWithValueHolder avgt5 13035.883 ± 196.081 ns/opIntBenchmarks.setWithWriter avgt5 24734.825 ± 1603.708 ns/op* For the *getInt *operation, there is little performance difference. This is because we disable the ARROW_ENABLE_NULL_CHECK_FOR_GET flag, so manipulations to the validity buffer are by-passed, even if the non-nullable vector flag is off. When the ARROW_ENABLE_NULL_CHECK_FOR_GET is enabled, there is a 72.4% performance improvement gained by turning on the non-nullable vector flag. For the isNull operation, we see 3 orders of magnitude performance improvements by enabling the non-nullable vector flag. For other operations, we see 12.2%, 13.5% and 14.5% performance improvements by turning on the non-nullable vector flag. So it can be seen that notable performance improvements can be gained for non-nullable vectors. *Third*, we want to claim that for nullable vectors and scenarios when we turn off the non-nullable vector flag, the new changes do not introduce performance regression. Such concern is plausible, as our changes add some if-else branches to the code, which may degrade performance. We give the benchmark results of the original code, as below. *(original ocde)* *Benchmark Mode Cnt Score Error UnitsIntBenchmarks.getInt avgt5383.511 ± 0.156 ns/opIntBenchmarks.isNull avgt5 1274.271 ± 19.092 ns/opIntBenchmarks.setIntDirectly avgt5 15162.219 ± 194.956 ns/opIntBenchmarks.setWithValueHolder avgt5 15247.640 ± 153.103 ns/opIntBenchmarks.setWithWriter avgt5 28587.780 ± 160.458 ns/op* By comparing this set of results with the above results with non-nullable vector flag disabled, little performance difference can be observed, indicating no performance regression. By examining the generated assembly, it can be seen that JIT is smart enough to remove the if-else branch completely (the below screen-shot gives an example where the if branch is optimized away in the assembly) So if some users do not like this feature, because their vectors are always nullable, they can simply disable the flag, and no performance difference can be observed. Would you please give some feedback? If it looks good to you, maybe we can go ahead to support other types of vectors. Thank you in advance. Liya Fan [image: image.png] [1] https://github.com/apache/arrow/pull/8147 On Fri, Mar 13, 2020 at 9:47 PM Fan Liya wrote: > Hi Jacques, > > Thanks a lot for your valuable comments. > > I agree with you that collapsing nullable and
Re: [DISCUSS][Java] Support non-nullable vectors
Hi Jacques, Thanks a lot for your valuable comments. I agree with you that collapsing nullable and non-nullable implementations is a good idea, and it does not contradict with the idea of introducing a fast code path, if it does not introduce much cost or code complexity. The idea of word level checking is interesting. As you suggested, we will do more investigations and reconsider the problem from a broader perspective. Best, Liya Fan On Thu, Mar 12, 2020 at 9:27 AM Jacques Nadeau wrote: > Generally Ive found that this isnt an important optimization in the use > cases we see. Memory overhead, especially with our Java shared allocation > scheme is nominal. Optimizing null checks at the word level usually is much > more impactful since non null and null runs are much more common on a > shorter window common than they seeing those declared. > > In other words, I'd suggest you look at your problem with a broader > perspective and see whether you're actually focused on optimizing the most > important dimension. > > As an aside, the original Arrow Java code actually treated these concepts > more distinctly and we consciously made a decision to collapse them to > simplify real world use. > > I do think it makes to add a dirty read interface if you want. This would > allow consumers of the interface to behave efficiently if they wanted to. > > One last note, efficient evaluation and processing should generally always > work at the validity word level. Adding an extra if check at the word > versus extra complexity of having an early out per batch seems like a > pretty small life in the grand scheme of processing. > > On Wed, Mar 11, 2020, 9:15 AM Brian Hulette wrote: > > > > And there is a "nullable" metadata-only flag at the > > > Field level. Could the same kinds of optimizations be implemented in > > > Java without introducing a "nullable" concept? > > > > Note Liya Fan did suggest pulling the nullable flag from the Field when > the > > vector is created in item (1) of the proposed changes. > > > > Brian > > > > On Wed, Mar 11, 2020 at 5:54 AM Fan Liya wrote: > > > > > Hi Micah, > > > > > > Thanks a lot for your valuable comments. Please see my comments inline. > > > > > > > I'm a little concerned that this will change assumptions for at least > > > some > > > > of the clients using the library (some might always rely on the > > validity > > > > buffer being present). > > > > > > I can understand your concern and I am also concerned. > > > IMO, the client should not depend on this assumption, as the > > specification > > > says "Arrays having a 0 null count may choose to not allocate the > > validity > > > bitmap." [1] > > > That being said, I think it would be safe to provide a global flag to > > > switch on/off the feature (as you suggested). > > > > > > > I think this is a good feature to have for the reasons you mentioned. > > It > > > > seems like there would need to be some sort of configuration bit to > set > > > for > > > > this behavior. > > > > > > Good suggestion. We should be able to switch on and off the feature > with > > a > > > single global flag. > > > > > > > But, I'd be worried about code complexity this would > > > > introduce. > > > > > > I agree with you that code complexity is an important factor to > consider. > > > IMO, our proposal should not involve too much code change, or increase > > code > > > complexity too much. > > > To prove this, maybe we need to show some small experimental code > change. > > > > > > Best, > > > Liya Fan > > > > > > [1] https://arrow.apache.org/docs/format/Columnar.html#logical-types > > > > > > On Wed, Mar 11, 2020 at 1:53 PM Micah Kornfield > > > > wrote: > > > > > > > Hi Liya Fan, > > > > I'm a little concerned that this will change assumptions for at least > > > some > > > > of the clients using the library (some might always rely on the > > validity > > > > buffer being present). > > > > > > > > I think this is a good feature to have for the reasons you mentioned. > > It > > > > seems like there would need to be some sort of configuration bit to > set > > > for > > > > this behavior. But, I'd be worried about code complexity this would > > > > introduce. > > > > > > > > Thanks, > > > > Micah > > > > > > > > On Tue, Mar 10, 2020 at 6:42 AM Fan Liya > wrote: > > > > > > > > > Hi Wes, > > > > > > > > > > Thanks a lot for your quick reply. > > > > > I think what you mentioned is almost exactly what we want to do in > > > > Java.The > > > > > concept is not important. > > > > > > > > > > Maybe there are only some minor differences: > > > > > 1. In C++, the null_count is mutable, while for Java, once a vector > > is > > > > > constructed as non-nullable, its null count can only be 0. > > > > > 2. In C++, a non-nullable array's validity buffer is null, while in > > > Java, > > > > > the buffer is an empty buffer, and cannot be changed. > > > > > > > > > > Best, > > > > > Liya Fan > > > > > > > > > > On Tue, Mar 10, 2020 at 9:26 PM Wes McKinney
Re: [DISCUSS][Java] Support non-nullable vectors
Generally Ive found that this isnt an important optimization in the use cases we see. Memory overhead, especially with our Java shared allocation scheme is nominal. Optimizing null checks at the word level usually is much more impactful since non null and null runs are much more common on a shorter window common than they seeing those declared. In other words, I'd suggest you look at your problem with a broader perspective and see whether you're actually focused on optimizing the most important dimension. As an aside, the original Arrow Java code actually treated these concepts more distinctly and we consciously made a decision to collapse them to simplify real world use. I do think it makes to add a dirty read interface if you want. This would allow consumers of the interface to behave efficiently if they wanted to. One last note, efficient evaluation and processing should generally always work at the validity word level. Adding an extra if check at the word versus extra complexity of having an early out per batch seems like a pretty small life in the grand scheme of processing. On Wed, Mar 11, 2020, 9:15 AM Brian Hulette wrote: > > And there is a "nullable" metadata-only flag at the > > Field level. Could the same kinds of optimizations be implemented in > > Java without introducing a "nullable" concept? > > Note Liya Fan did suggest pulling the nullable flag from the Field when the > vector is created in item (1) of the proposed changes. > > Brian > > On Wed, Mar 11, 2020 at 5:54 AM Fan Liya wrote: > > > Hi Micah, > > > > Thanks a lot for your valuable comments. Please see my comments inline. > > > > > I'm a little concerned that this will change assumptions for at least > > some > > > of the clients using the library (some might always rely on the > validity > > > buffer being present). > > > > I can understand your concern and I am also concerned. > > IMO, the client should not depend on this assumption, as the > specification > > says "Arrays having a 0 null count may choose to not allocate the > validity > > bitmap." [1] > > That being said, I think it would be safe to provide a global flag to > > switch on/off the feature (as you suggested). > > > > > I think this is a good feature to have for the reasons you mentioned. > It > > > seems like there would need to be some sort of configuration bit to set > > for > > > this behavior. > > > > Good suggestion. We should be able to switch on and off the feature with > a > > single global flag. > > > > > But, I'd be worried about code complexity this would > > > introduce. > > > > I agree with you that code complexity is an important factor to consider. > > IMO, our proposal should not involve too much code change, or increase > code > > complexity too much. > > To prove this, maybe we need to show some small experimental code change. > > > > Best, > > Liya Fan > > > > [1] https://arrow.apache.org/docs/format/Columnar.html#logical-types > > > > On Wed, Mar 11, 2020 at 1:53 PM Micah Kornfield > > wrote: > > > > > Hi Liya Fan, > > > I'm a little concerned that this will change assumptions for at least > > some > > > of the clients using the library (some might always rely on the > validity > > > buffer being present). > > > > > > I think this is a good feature to have for the reasons you mentioned. > It > > > seems like there would need to be some sort of configuration bit to set > > for > > > this behavior. But, I'd be worried about code complexity this would > > > introduce. > > > > > > Thanks, > > > Micah > > > > > > On Tue, Mar 10, 2020 at 6:42 AM Fan Liya wrote: > > > > > > > Hi Wes, > > > > > > > > Thanks a lot for your quick reply. > > > > I think what you mentioned is almost exactly what we want to do in > > > Java.The > > > > concept is not important. > > > > > > > > Maybe there are only some minor differences: > > > > 1. In C++, the null_count is mutable, while for Java, once a vector > is > > > > constructed as non-nullable, its null count can only be 0. > > > > 2. In C++, a non-nullable array's validity buffer is null, while in > > Java, > > > > the buffer is an empty buffer, and cannot be changed. > > > > > > > > Best, > > > > Liya Fan > > > > > > > > On Tue, Mar 10, 2020 at 9:26 PM Wes McKinney > > > wrote: > > > > > > > > > hi Liya, > > > > > > > > > > In C++ we elect certain faster code paths when the null count is 0 > or > > > > > computed to be zero. When the null count is 0, we do not allocate a > > > > > validity bitmap. And there is a "nullable" metadata-only flag at > the > > > > > Field level. Could the same kinds of optimizations be implemented > in > > > > > Java without introducing a "nullable" concept? > > > > > > > > > > - Wes > > > > > > > > > > On Tue, Mar 10, 2020 at 8:13 AM Fan Liya > > wrote: > > > > > > > > > > > > Dear all, > > > > > > > > > > > > A non-nullable vector is one that is guaranteed to contain no > > nulls. > > > We > > > > > > want to support non-nullable vectors in Java. > > > > > > > > > > > >
Re: [DISCUSS][Java] Support non-nullable vectors
> And there is a "nullable" metadata-only flag at the > Field level. Could the same kinds of optimizations be implemented in > Java without introducing a "nullable" concept? Note Liya Fan did suggest pulling the nullable flag from the Field when the vector is created in item (1) of the proposed changes. Brian On Wed, Mar 11, 2020 at 5:54 AM Fan Liya wrote: > Hi Micah, > > Thanks a lot for your valuable comments. Please see my comments inline. > > > I'm a little concerned that this will change assumptions for at least > some > > of the clients using the library (some might always rely on the validity > > buffer being present). > > I can understand your concern and I am also concerned. > IMO, the client should not depend on this assumption, as the specification > says "Arrays having a 0 null count may choose to not allocate the validity > bitmap." [1] > That being said, I think it would be safe to provide a global flag to > switch on/off the feature (as you suggested). > > > I think this is a good feature to have for the reasons you mentioned. It > > seems like there would need to be some sort of configuration bit to set > for > > this behavior. > > Good suggestion. We should be able to switch on and off the feature with a > single global flag. > > > But, I'd be worried about code complexity this would > > introduce. > > I agree with you that code complexity is an important factor to consider. > IMO, our proposal should not involve too much code change, or increase code > complexity too much. > To prove this, maybe we need to show some small experimental code change. > > Best, > Liya Fan > > [1] https://arrow.apache.org/docs/format/Columnar.html#logical-types > > On Wed, Mar 11, 2020 at 1:53 PM Micah Kornfield > wrote: > > > Hi Liya Fan, > > I'm a little concerned that this will change assumptions for at least > some > > of the clients using the library (some might always rely on the validity > > buffer being present). > > > > I think this is a good feature to have for the reasons you mentioned. It > > seems like there would need to be some sort of configuration bit to set > for > > this behavior. But, I'd be worried about code complexity this would > > introduce. > > > > Thanks, > > Micah > > > > On Tue, Mar 10, 2020 at 6:42 AM Fan Liya wrote: > > > > > Hi Wes, > > > > > > Thanks a lot for your quick reply. > > > I think what you mentioned is almost exactly what we want to do in > > Java.The > > > concept is not important. > > > > > > Maybe there are only some minor differences: > > > 1. In C++, the null_count is mutable, while for Java, once a vector is > > > constructed as non-nullable, its null count can only be 0. > > > 2. In C++, a non-nullable array's validity buffer is null, while in > Java, > > > the buffer is an empty buffer, and cannot be changed. > > > > > > Best, > > > Liya Fan > > > > > > On Tue, Mar 10, 2020 at 9:26 PM Wes McKinney > > wrote: > > > > > > > hi Liya, > > > > > > > > In C++ we elect certain faster code paths when the null count is 0 or > > > > computed to be zero. When the null count is 0, we do not allocate a > > > > validity bitmap. And there is a "nullable" metadata-only flag at the > > > > Field level. Could the same kinds of optimizations be implemented in > > > > Java without introducing a "nullable" concept? > > > > > > > > - Wes > > > > > > > > On Tue, Mar 10, 2020 at 8:13 AM Fan Liya > wrote: > > > > > > > > > > Dear all, > > > > > > > > > > A non-nullable vector is one that is guaranteed to contain no > nulls. > > We > > > > > want to support non-nullable vectors in Java. > > > > > > > > > > *Motivations:* > > > > > 1. It is widely used in practice. For example, in a database > engine, > > a > > > > > column can be declared as not null, so it cannot contain null > values. > > > > > 2.Non-nullable vectors has significant performance advantages > > compared > > > > with > > > > > their nullable conterparts, such as: > > > > > 1) the memory space of the validity buffer can be saved. > > > > > 2) manipulation of the validity buffer can be bypassed > > > > > 3) some if-else branches can be replaced by sequential > instructions > > > (by > > > > > the JIT compiler), leading to high throughput for the CPU pipeline. > > > > > > > > > > *Potential Cost:* > > > > > For nullable vectors, there can be extra checks against the > > > nullablility > > > > > flag. So we must change the code in a way that minimizes the cost. > > > > > > > > > > *Proposed Changes:* > > > > > 1. There is no need to create new vector classes. We add a final > > > boolean > > > > to > > > > > the vector base classes as the nullability flag. The value of the > > flag > > > > can > > > > > be obtained from the field when creating the vector. > > > > > 2. Add a method "boolean isNullable()" to the root interface > > > ValueVector. > > > > > 3. If a vector is non-nullable, its validity buffer should be an > > empty > > > > > buffer (not null, so much of the existing logic can be left > >
Re: [DISCUSS][Java] Support non-nullable vectors
Hi Micah, Thanks a lot for your valuable comments. Please see my comments inline. > I'm a little concerned that this will change assumptions for at least some > of the clients using the library (some might always rely on the validity > buffer being present). I can understand your concern and I am also concerned. IMO, the client should not depend on this assumption, as the specification says "Arrays having a 0 null count may choose to not allocate the validity bitmap." [1] That being said, I think it would be safe to provide a global flag to switch on/off the feature (as you suggested). > I think this is a good feature to have for the reasons you mentioned. It > seems like there would need to be some sort of configuration bit to set for > this behavior. Good suggestion. We should be able to switch on and off the feature with a single global flag. > But, I'd be worried about code complexity this would > introduce. I agree with you that code complexity is an important factor to consider. IMO, our proposal should not involve too much code change, or increase code complexity too much. To prove this, maybe we need to show some small experimental code change. Best, Liya Fan [1] https://arrow.apache.org/docs/format/Columnar.html#logical-types On Wed, Mar 11, 2020 at 1:53 PM Micah Kornfield wrote: > Hi Liya Fan, > I'm a little concerned that this will change assumptions for at least some > of the clients using the library (some might always rely on the validity > buffer being present). > > I think this is a good feature to have for the reasons you mentioned. It > seems like there would need to be some sort of configuration bit to set for > this behavior. But, I'd be worried about code complexity this would > introduce. > > Thanks, > Micah > > On Tue, Mar 10, 2020 at 6:42 AM Fan Liya wrote: > > > Hi Wes, > > > > Thanks a lot for your quick reply. > > I think what you mentioned is almost exactly what we want to do in > Java.The > > concept is not important. > > > > Maybe there are only some minor differences: > > 1. In C++, the null_count is mutable, while for Java, once a vector is > > constructed as non-nullable, its null count can only be 0. > > 2. In C++, a non-nullable array's validity buffer is null, while in Java, > > the buffer is an empty buffer, and cannot be changed. > > > > Best, > > Liya Fan > > > > On Tue, Mar 10, 2020 at 9:26 PM Wes McKinney > wrote: > > > > > hi Liya, > > > > > > In C++ we elect certain faster code paths when the null count is 0 or > > > computed to be zero. When the null count is 0, we do not allocate a > > > validity bitmap. And there is a "nullable" metadata-only flag at the > > > Field level. Could the same kinds of optimizations be implemented in > > > Java without introducing a "nullable" concept? > > > > > > - Wes > > > > > > On Tue, Mar 10, 2020 at 8:13 AM Fan Liya wrote: > > > > > > > > Dear all, > > > > > > > > A non-nullable vector is one that is guaranteed to contain no nulls. > We > > > > want to support non-nullable vectors in Java. > > > > > > > > *Motivations:* > > > > 1. It is widely used in practice. For example, in a database engine, > a > > > > column can be declared as not null, so it cannot contain null values. > > > > 2.Non-nullable vectors has significant performance advantages > compared > > > with > > > > their nullable conterparts, such as: > > > > 1) the memory space of the validity buffer can be saved. > > > > 2) manipulation of the validity buffer can be bypassed > > > > 3) some if-else branches can be replaced by sequential instructions > > (by > > > > the JIT compiler), leading to high throughput for the CPU pipeline. > > > > > > > > *Potential Cost:* > > > > For nullable vectors, there can be extra checks against the > > nullablility > > > > flag. So we must change the code in a way that minimizes the cost. > > > > > > > > *Proposed Changes:* > > > > 1. There is no need to create new vector classes. We add a final > > boolean > > > to > > > > the vector base classes as the nullability flag. The value of the > flag > > > can > > > > be obtained from the field when creating the vector. > > > > 2. Add a method "boolean isNullable()" to the root interface > > ValueVector. > > > > 3. If a vector is non-nullable, its validity buffer should be an > empty > > > > buffer (not null, so much of the existing logic can be left > unchanged). > > > > 4. For operations involving validity buffers (e.g. isNull, get, set), > > we > > > > use the nullability flag to bypass manipulations to the validity > > buffer. > > > > > > > > Therefore, it should be possible to support the feature with small > code > > > > changes. > > > > > > > > BTW, please note that similar behaviors have already been supported > in > > > C++. > > > > > > > > Would you please give your valueable feedback? > > > > > > > > Best, > > > > Liya Fan > > > > > >
Re: [DISCUSS][Java] Support non-nullable vectors
Hi Liya Fan, I'm a little concerned that this will change assumptions for at least some of the clients using the library (some might always rely on the validity buffer being present). I think this is a good feature to have for the reasons you mentioned. It seems like there would need to be some sort of configuration bit to set for this behavior. But, I'd be worried about code complexity this would introduce. Thanks, Micah On Tue, Mar 10, 2020 at 6:42 AM Fan Liya wrote: > Hi Wes, > > Thanks a lot for your quick reply. > I think what you mentioned is almost exactly what we want to do in Java.The > concept is not important. > > Maybe there are only some minor differences: > 1. In C++, the null_count is mutable, while for Java, once a vector is > constructed as non-nullable, its null count can only be 0. > 2. In C++, a non-nullable array's validity buffer is null, while in Java, > the buffer is an empty buffer, and cannot be changed. > > Best, > Liya Fan > > On Tue, Mar 10, 2020 at 9:26 PM Wes McKinney wrote: > > > hi Liya, > > > > In C++ we elect certain faster code paths when the null count is 0 or > > computed to be zero. When the null count is 0, we do not allocate a > > validity bitmap. And there is a "nullable" metadata-only flag at the > > Field level. Could the same kinds of optimizations be implemented in > > Java without introducing a "nullable" concept? > > > > - Wes > > > > On Tue, Mar 10, 2020 at 8:13 AM Fan Liya wrote: > > > > > > Dear all, > > > > > > A non-nullable vector is one that is guaranteed to contain no nulls. We > > > want to support non-nullable vectors in Java. > > > > > > *Motivations:* > > > 1. It is widely used in practice. For example, in a database engine, a > > > column can be declared as not null, so it cannot contain null values. > > > 2.Non-nullable vectors has significant performance advantages compared > > with > > > their nullable conterparts, such as: > > > 1) the memory space of the validity buffer can be saved. > > > 2) manipulation of the validity buffer can be bypassed > > > 3) some if-else branches can be replaced by sequential instructions > (by > > > the JIT compiler), leading to high throughput for the CPU pipeline. > > > > > > *Potential Cost:* > > > For nullable vectors, there can be extra checks against the > nullablility > > > flag. So we must change the code in a way that minimizes the cost. > > > > > > *Proposed Changes:* > > > 1. There is no need to create new vector classes. We add a final > boolean > > to > > > the vector base classes as the nullability flag. The value of the flag > > can > > > be obtained from the field when creating the vector. > > > 2. Add a method "boolean isNullable()" to the root interface > ValueVector. > > > 3. If a vector is non-nullable, its validity buffer should be an empty > > > buffer (not null, so much of the existing logic can be left unchanged). > > > 4. For operations involving validity buffers (e.g. isNull, get, set), > we > > > use the nullability flag to bypass manipulations to the validity > buffer. > > > > > > Therefore, it should be possible to support the feature with small code > > > changes. > > > > > > BTW, please note that similar behaviors have already been supported in > > C++. > > > > > > Would you please give your valueable feedback? > > > > > > Best, > > > Liya Fan > > >
Re: [DISCUSS][Java] Support non-nullable vectors
Hi Wes, Thanks a lot for your quick reply. I think what you mentioned is almost exactly what we want to do in Java.The concept is not important. Maybe there are only some minor differences: 1. In C++, the null_count is mutable, while for Java, once a vector is constructed as non-nullable, its null count can only be 0. 2. In C++, a non-nullable array's validity buffer is null, while in Java, the buffer is an empty buffer, and cannot be changed. Best, Liya Fan On Tue, Mar 10, 2020 at 9:26 PM Wes McKinney wrote: > hi Liya, > > In C++ we elect certain faster code paths when the null count is 0 or > computed to be zero. When the null count is 0, we do not allocate a > validity bitmap. And there is a "nullable" metadata-only flag at the > Field level. Could the same kinds of optimizations be implemented in > Java without introducing a "nullable" concept? > > - Wes > > On Tue, Mar 10, 2020 at 8:13 AM Fan Liya wrote: > > > > Dear all, > > > > A non-nullable vector is one that is guaranteed to contain no nulls. We > > want to support non-nullable vectors in Java. > > > > *Motivations:* > > 1. It is widely used in practice. For example, in a database engine, a > > column can be declared as not null, so it cannot contain null values. > > 2.Non-nullable vectors has significant performance advantages compared > with > > their nullable conterparts, such as: > > 1) the memory space of the validity buffer can be saved. > > 2) manipulation of the validity buffer can be bypassed > > 3) some if-else branches can be replaced by sequential instructions (by > > the JIT compiler), leading to high throughput for the CPU pipeline. > > > > *Potential Cost:* > > For nullable vectors, there can be extra checks against the nullablility > > flag. So we must change the code in a way that minimizes the cost. > > > > *Proposed Changes:* > > 1. There is no need to create new vector classes. We add a final boolean > to > > the vector base classes as the nullability flag. The value of the flag > can > > be obtained from the field when creating the vector. > > 2. Add a method "boolean isNullable()" to the root interface ValueVector. > > 3. If a vector is non-nullable, its validity buffer should be an empty > > buffer (not null, so much of the existing logic can be left unchanged). > > 4. For operations involving validity buffers (e.g. isNull, get, set), we > > use the nullability flag to bypass manipulations to the validity buffer. > > > > Therefore, it should be possible to support the feature with small code > > changes. > > > > BTW, please note that similar behaviors have already been supported in > C++. > > > > Would you please give your valueable feedback? > > > > Best, > > Liya Fan >