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https://issues.apache.org/jira/browse/DRILL-5490?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16002056#comment-16002056
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Paul Rogers commented on DRILL-5490:
------------------------------------
More bizarre. In actual use, {{recordStart}} is, in fact, 0 during the record.
But, when extracting headers, the header is read, then {{finishRecord()}} is
called:
{code}
public void finishRecord() {
recordStart = characterData;
{code}
At this point, {{recordStart}} is set to "record end"...
So, this line actually works:
{code}
if (this.recordStart != characterData) {
throw new ExecutionSetupException("record text was requested before
finishing record");
}
{code}
But, it works in the sense that {{recordStart}} and {{characterData}} both
point to the *end* of the record. If it were not for the issue described in
DRILL-5491, the logic would be that {{recordStart}} would be zero if we didn't
finish the record, but we we always do, so the check is a complete no-op.
> RepeatedVarCharOutput.recordStart becomes corrupted on realloc
> --------------------------------------------------------------
>
> Key: DRILL-5490
> URL: https://issues.apache.org/jira/browse/DRILL-5490
> Project: Apache Drill
> Issue Type: Bug
> Affects Versions: 1.10.0
> Reporter: Paul Rogers
> Priority: Minor
>
> The class {{RepeatedVarCharOutput}}, used to read text data into the
> {{columns}} array, has a member called {{recordStart}} which is supposed to
> track the memory offset of the start of the record data in the {{columns}}
> VarChar array. However, the logic for the member is very wrong. First, it is
> initialized based on an uninitialized variable:
> {{code}}
> public void startBatch() {
> this.recordStart = characterDataOriginal;
> ...
> loadVarCharDataAddress();
> }
> private void loadVarCharDataAddress(){
> ...
> this.characterDataOriginal = buf.memoryAddress();
> ...
> }
> {{code}}
> Second, the class keeps track of actual memory addresses for the VarChar
> data. When data would exceed the buffer, memory is reallocated using the
> following method. But, this method *does not* adjust the {{recordStart}}
> member, which now points to a bogus memory address:
> {code}
> private void expandVarCharData(){
> vector.getDataVector().reAlloc();
> long diff = characterData - characterDataOriginal;
> loadVarCharDataAddress();
> characterData += diff;
> }
> {code}
> Fortunately, like so many bugs in this class, these bugs are offset by the
> fact that the variable is never used in a way that cause obvious problems
> (else these issues would have been found sooner.) The only real use is:
> {code}
> @Override
> public boolean rowHasData() {
> return recordStart < characterData;
> }
> {code}
> Which, it turns out, is used only at EOF in {{TextReader.parseRecord()}}:
> {code}
> } catch(StreamFinishedPseudoException e) {
> // if we've written part of a field or all of a field, we should send
> this row.
> if (fieldsWritten == 0 && !output.rowHasData()) {
> throw e;
> }
> }
> {code}
> Thus, the bug will cause a failure only if:
> * A batch is resized, and
> * The new address is lower than the original address, and
> * It is the last batch in the file.
> Because of the low probability of hitting the bug, the priority is set to
> Minor.
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