prestodb/presto · error · IllegalArgumentException

position is not valid

Error message

position is not valid

What it means

ShortArrayBlockBuilder.checkReadablePosition validates positions before reads (getByte, isNull, writePositionTo, getSingleValueBlock, copyPositions). Positions must satisfy 0 <= position < positionCount (built entries so far). Out-of-range positions throw IllegalArgumentException("position is not valid").

Source

Thrown at presto-common/src/main/java/com/facebook/presto/common/block/ShortArrayBlockBuilder.java:328

        return new ShortArrayBlock(0, length, newValueIsNull, newValues);
    }

    @Override
    public String getEncodingName()
    {
        return ShortArrayBlockEncoding.NAME;
    }

    @Override
    public String toString()
    {
        return format("ShortArrayBlockBuilder(%d){positionCount=%d}", hashCode(), getPositionCount());
    }

    private void checkReadablePosition(int position)
    {
        if (position < 0 || position >= getPositionCount()) {
            throw new IllegalArgumentException("position is not valid");
        }
    }

    @Override
    public short getShortUnchecked(int internalPosition)
    {
        assert internalPositionInRange(internalPosition, getOffsetBase(), getPositionCount());
        return values[internalPosition];
    }

    @Override
    public boolean isNullUnchecked(int internalPosition)
    {
        assert mayHaveNull() : "no nulls present";
        assert internalPositionInRange(internalPosition, getOffsetBase(), getPositionCount());
        return valueIsNull[internalPosition];
    }

View on GitHub (pinned to 55bb57d202)

Solutions

1. Verify builder.getPositionCount() > position before reading.
2. After reset()/newInstance, do not reuse old indices; re-read entries only up to the new positionCount.
3. Ensure the builder was fully populated (close/advance entry) before reading its values.

Example fix

// before
builder.reset();
short v = builder.getShort(0, 0); // throws: positionCount is 0
// after
builder.reset();
if (builder.getPositionCount() > 0) {
    short v = builder.getShort(0, 0);
}

if (position < 0 || position >= builder.getPositionCount()) {
    throw new IllegalArgumentException("position " + position + " not yet written to builder (count=" + builder.getPositionCount() + ")");
}

boolean builderHasPosition(BlockBuilder builder, int position) {
    return position >= 0 && position < builder.getPositionCount();
}

try {
    value = builder.getShort(position, 0);
} catch (IllegalArgumentException e) {
    if (e.getMessage().equals("position is not valid")) {
        log.warn("read at %d but builder has %d entries", position, builder.getPositionCount());
        return null;
    }
    throw e;
}

When it happens

Trigger: Reading from a ShortArrayBlockBuilder before it has enough entries, or with a negative index; e.g. calling getPositionCount()-dependent accessors with stale index after builder.reset().

Common situations: Reading a builder that was just reset (positionCount = 0), reading position positionCount-1 + 1 in a loop, mixing up builder entry count with expected row count, off-by-one in composite-type field access (getByte with wrong field offset confusion).

Related errors

• position is not valid
• position is not valid
• position is not valid
• position is not valid
• position is not valid

AI-assisted analysis of prestodb/presto@55bb57d202 (2026-09-04). Data as JSON: /api/errors/1dc9aa92d10998c0. Report an issue: GitHub.