szehon-ho commented on code in PR #8755:
URL: https://github.com/apache/iceberg/pull/8755#discussion_r1452867560
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api/src/main/java/org/apache/iceberg/types/TypeUtil.java:
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@@ -452,6 +454,68 @@ private static void checkSchemaCompatibility(
}
}
+ /**
+ * Estimates the number of bytes a value for a given field may occupy in
memory.
+ *
+ * <p>This method approximates the memory size based on the internal Java
representation defined
+ * by {@link Type.TypeID}. It is important to note that the actual size
might differ from this
+ * estimation. The method is designed to handle a variety of data types,
including primitive
+ * types, strings, and nested types such as structs, maps, and lists.
+ *
+ * @param field a field for which to estimate the size
+ * @return the estimated size in bytes of the field's value in memory
+ */
+ public static long defaultSize(Types.NestedField field) {
+ return defaultSize(field.type());
+ }
+
+ private static long defaultSize(Type type) {
+ switch (type.typeId()) {
+ case BOOLEAN:
+ // the size of a boolean variable is virtual machine dependent
+ // it is common to believe booleans occupy 1 byte in most JVMs
+ return 1;
+ case INTEGER:
+ case FLOAT:
+ case DATE:
+ // ints and floats occupy 4 bytes
+ // dates are internally represented as ints
+ return 4;
+ case LONG:
+ case DOUBLE:
+ case TIME:
+ case TIMESTAMP:
+ // longs and doubles occupy 8 bytes
+ // times and timestamps are internally represented as longs
+ return 8;
+ case STRING:
+ // 12 (header) + 12 (fields) + 16 (array overhead) + 20 (10 chars, 2
bytes each) = 60 bytes
+ return 60;
+ case UUID:
+ // 12 (header) + 16 (two long variables) = 28 bytes
+ return 28;
+ case FIXED:
+ return ((Types.FixedType) type).length();
+ case BINARY:
+ return 100;
+ case DECIMAL:
+ // 12 (header) + (12 + 12 + 4) (BigInteger) + 4 (scale) = 44 bytes
+ return 44;
+ case STRUCT:
+ Types.StructType struct = (Types.StructType) type;
+ return OBJECT_HEADER +
struct.fields().stream().mapToLong(TypeUtil::defaultSize).sum();
+ case LIST:
+ Types.ListType list = (Types.ListType) type;
+ return OBJECT_HEADER + 5 * defaultSize(list.elementType());
+ case MAP:
+ Types.MapType map = (Types.MapType) type;
+ long entrySize = OBJECT_HEADER + defaultSize(map.keyType()) +
defaultSize(map.valueType());
+ return OBJECT_HEADER + 5 * entrySize;
+ default:
+ return 16;
Review Comment:
Agree its not in the critical path. I was more thinking in the lines of ,
if i ever add a new type, how will i know to add a estimate here? Hopefully
here a unit test will fail, and we will soon add a proper estimate.
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