// Use the average object size to estimate how many objects a full chunk would carry do that
// while traversing the chunk's range using the sharding index, below there's a fair amount of
// slack before we determine a chunk is too large because object sizes will vary.
unsigned long long maxRecsWhenFull;
long long avgRecSize;

const long long totalRecs = collection->numRecords(opCtx);
if (totalRecs > 0) {
    avgRecSize = collection->dataSize(opCtx) / totalRecs;
    // The calls to numRecords() and dataSize() are not atomic so it is possible that the data
    // size becomes smaller than the number of records between the two calls, which would result
    // in average record size of zero
    if (avgRecSize == 0) {
        avgRecSize = BSONObj::kMinBSONLength;
    }
    maxRecsWhenFull = _args.getMaxChunkSizeBytes() / avgRecSize;
    maxRecsWhenFull = 130 * maxRecsWhenFull / 100;  // pad some slack
} else {
    avgRecSize = 0;
    maxRecsWhenFull = kMaxObjectPerChunk + 1;
}