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Paul Rogers commented on DRILL-5602: ------------------------------------ It appears that other vectors have the same issue. * Repeated map vector (discussed above) * Variable-width vector (see below) * All repeated value vectors (see below) The {{ListVector}} does not have the problem because it does not have the {{allocateNew(int valueCount)}} method. This is its own bug... The following is code from the {{VarCharVector}}: {code} @Override public void allocateNew(int totalBytes, int valueCount) { ... offsetVector.allocateNew(valueCount + 1); ... data.readerIndex(0); allocationSizeInBytes = totalBytes; offsetVector.zeroVector(); } {code} Notice that the above does not set the initial offset to zero. Typical repeated vector code (from {{RepeatedIntVector}}: {code} @Override public void allocateNew(int valueCount, int innerValueCount) { ... offsets.allocateNew(valueCount + 1); values.allocateNew(innerValueCount); ... offsets.zeroVector(); mutator.reset(); } {code} For {{RepeatedListVector}}: {code} @Override public void allocateNew(int valueCount, int innerValueCount) { clear(); getOffsetVector().allocateNew(valueCount + 1); getMutator().reset(); } {code} > Vector corruption when allocating a repeated, variable-width vector > ------------------------------------------------------------------- > > Key: DRILL-5602 > URL: https://issues.apache.org/jira/browse/DRILL-5602 > Project: Apache Drill > Issue Type: Bug > Affects Versions: 1.10.0 > Reporter: Paul Rogers > Assignee: Paul Rogers > Fix For: 1.11.0 > > > The query in DRILL-5513 highlighted a problem described in DRILL-5594: that > the external sort did not properly allocate its spill batch vectors, and > instead allowed them to grow by doubling. While fixing that issue, a new > issue became clear. > The method to allocate a repeated map vector, however, has a serious bug, as > described in DRILL-5530: value vectors do not zero-fill the first allocation > for a vector (though subsequent reallocs are zero-filled.) > If the code worked correctly, here is the behavior when writing to the first > element of the list: > * Access the offset vector at offset 0. Should be 0. > * Write the new value at that offset. Since the first offset is 0, the first > value is written at 0 in the value vector. > * Write into offset 1 the value at offset 0 plus the length of the new value. > But, the offset vector is not initialized to zero. Instead, offset 0 contains > the value 16 million. Now: > * Access the offset vector at offset 0. Value is 16 million. > * Write the new value at that offset. Write at position 16 million. This > requires growing the value vector from its present size to 16 MB. > The problem is here in {{RepeatedMapVector}}: > {code} > public void allocateOffsetsNew(int groupCount) { > offsets.allocateNew(groupCount + 1); > } > {code} > Notice that there is no code to set the value at offset 0. > Then, in the {{UInt4Vector}}: > {code} > public void allocateNew(final int valueCount) { > allocateBytes(valueCount * 4); > } > private void allocateBytes(final long size) { > ... > data = allocator.buffer(curSize); > ... > {code} > The above eventually calls the Netty memory allocator, which explicitly > states that, for performance reasons, it does not zero-fill its buffers. > The code works in small tests because the new buffer comes from Java direct > memory, which *does* zero-fill the buffer. -- This message was sent by Atlassian JIRA (v6.4.14#64029)