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https://issues.apache.org/jira/browse/ARROW-2019?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16338423#comment-16338423
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ASF GitHub Bot commented on ARROW-2019:
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jacques-n commented on a change in pull request #1497: ARROW-2019: [JAVA]
Control the memory allocated for inner vector in LIST
URL: https://github.com/apache/arrow/pull/1497#discussion_r163711284
##########
File path:
java/vector/src/main/java/org/apache/arrow/vector/BaseVariableWidthVector.java
##########
@@ -169,6 +169,45 @@ public void setInitialCapacity(int valueCount) {
offsetAllocationSizeInBytes = (valueCount + 1) * OFFSET_WIDTH;
}
+ /**
+ * Sets the desired value capacity for the vector. This function doesn't
+ * allocate any memory for the vector.
+ * @param valueCount desired number of elements in the vector
+ * @param density average number of bytes per variable width element
+ */
+ public void setInitialCapacity(int valueCount, double density) {
+ final long size = (long) (valueCount * density);
+ if (size > MAX_ALLOCATION_SIZE) {
+ throw new OversizedAllocationException("Requested amount of memory is
more than max allowed");
+ }
+ valueAllocationSizeInBytes = (int) size;
+ validityAllocationSizeInBytes = getValidityBufferSizeFromCount(valueCount);
+ /* to track the end offset of last data element in vector, we need
+ * an additional slot in offset buffer.
+ */
+ offsetAllocationSizeInBytes = (valueCount + 1) * OFFSET_WIDTH;
+ }
+
+ /**
+ * Get the density of this ListVector
+ * @return density
+ */
+ public double getDensity() {
+ if (valueCount == 0) {
+ return 0.0D;
+ }
+ double totalDataSize = 0.0D;
+ for (int i = 0; i < valueCount; i++) {
+ if (isSet(i) == 1) {
Review comment:
this can be done in aggregate, no need for loop.
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> Control the memory allocated for inner vector in LIST
> -----------------------------------------------------
>
> Key: ARROW-2019
> URL: https://issues.apache.org/jira/browse/ARROW-2019
> Project: Apache Arrow
> Issue Type: Improvement
> Reporter: Siddharth Teotia
> Assignee: Siddharth Teotia
> Priority: Critical
> Labels: pull-request-available
>
> We have observed cases in our external sort code where the amount of memory
> actually allocated for a record batch sometimes turns out to be more than
> necessary and also more than what was reserved by the operator for special
> purposes. Thus queries fail with OOM.
> Usually to control the memory allocated by vector.allocateNew() is to do a
> setInitialCapacity() and the latter modifies the vector state variables which
> are then used to allocate memory. However, due to the multiplier of 5 used in
> List Vector, we end up asking for more memory than necessary. For example,
> for a value count of 4095, we asked for 128KB of memory for an offset buffer
> of VarCharVector for a field which was list of varchars.
> We did ((4095 * 5) + 1) * 4 => 80KB . => 128KB (rounded off to power of 2
> allocation).
> We had earlier made changes to setInitialCapacity() of ListVector when we
> were facing problems with deeply nested lists and decided to use the
> multiplier only for the leaf scalar vector.
> It looks like there is a need for a specialized setInitialCapacity() for
> ListVector where the caller dictates the repeatedness.
> Also, there is another bug in setInitialCapacity() where the allocation of
> validity buffer doesn't obey the capacity specified in setInitialCapacity().
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