rzhang10 commented on a change in pull request #4301: URL: https://github.com/apache/iceberg/pull/4301#discussion_r834789462
##########
File path: format/spec.md
##########
@@ -951,24 +958,45 @@ Types are serialized according to this table:
|Type|JSON representation|Example|
|--- |--- |--- |
-|**`boolean`**|`JSON string: "boolean"`|`"boolean"`|
-|**`int`**|`JSON string: "int"`|`"int"`|
-|**`long`**|`JSON string: "long"`|`"long"`|
-|**`float`**|`JSON string: "float"`|`"float"`|
-|**`double`**|`JSON string: "double"`|`"double"`|
-|**`date`**|`JSON string: "date"`|`"date"`|
-|**`time`**|`JSON string: "time"`|`"time"`|
-|**`timestamp without zone`**|`JSON string: "timestamp"`|`"timestamp"`|
-|**`timestamp with zone`**|`JSON string: "timestamptz"`|`"timestamptz"`|
-|**`string`**|`JSON string: "string"`|`"string"`|
-|**`uuid`**|`JSON string: "uuid"`|`"uuid"`|
-|**`fixed(L)`**|`JSON string: "fixed[<L>]"`|`"fixed[16]"`|
-|**`binary`**|`JSON string: "binary"`|`"binary"`|
-|**`decimal(P, S)`**|`JSON string: "decimal(<P>,<S>)"`|`"decimal(9,2)"`,<br
/>`"decimal(9, 2)"`|
-|**`struct`**|`JSON object: {`<br /> `"type": "struct",`<br
/> `"fields": [ {`<br /> `"id": <field id
int>,`<br /> `"name": <name string>,`<br
/> `"required": <boolean>,`<br
/> `"type": <type JSON>,`<br
/> `"doc": <comment string>`<br
/> `}, ...`<br /> `] }`|`{`<br
/> `"type": "struct",`<br /> `"fields": [ {`<br
/> `"id": 1,`<br /> `"name":
"id",`<br /> `"required": true,`<br
/> `"type": "uuid"`<br /> `}, {`<br
/> `"id": 2,`<br /> `"name":
"data",`<br /> `"required": false,`<br
/> `"type": {`<br
/> `"type": "list",`<br
/> `...`<br />
`}`<br /> `} ]`<br />`}`|
-|**`list`**|`JSON object: {`<br /> `"type": "list",`<br
/> `"element-id": <id int>,`<br /> `"element-required":
<bool>`<br /> `"element": <type JSON>`<br />`}`|`{`<br
/> `"type": "list",`<br /> `"element-id": 3,`<br
/> `"element-required": true,`<br /> `"element":
"string"`<br />`}`|
-|**`map`**|`JSON object: {`<br /> `"type": "map",`<br
/> `"key-id": <key id int>,`<br /> `"key": <type
JSON>,`<br /> `"value-id": <val id int>,`<br
/> `"value-required": <bool>`<br /> `"value": <type
JSON>`<br />`}`|`{`<br /> `"type": "map",`<br
/> `"key-id": 4,`<br /> `"key": "string",`<br
/> `"value-id": 5,`<br /> `"value-required": false,`<br
/> `"value": "double"`<br />`}`|
-
+| **`boolean`** | `JSON string: "boolean"`
| `"boolean"`
|
+| **`int`** | `JSON string: "int"`
| `"int"`
|
+| **`long`** | `JSON string: "long"`
| `"long"`
|
+| **`float`** | `JSON string: "float"`
| `"float"`
|
+| **`double`** | `JSON string: "double"`
| `"double"`
|
+| **`date`** | `JSON string: "date"`
| `"date"`
|
+| **`time`** | `JSON string: "time"`
| `"time"`
|
+| **`timestamp without zone`** | `JSON string: "timestamp"`
| `"timestamp"`
|
+| **`timestamp with zone`** | `JSON string: "timestamptz"`
| `"timestamptz"`
|
+| **`string`** | `JSON string: "string"`
| `"string"`
|
+| **`uuid`** | `JSON string: "uuid"`
| `"uuid"`
|
+| **`fixed(L)`** | `JSON string: "fixed[<L>]"`
| `"fixed[16]"`
|
+| **`binary`** | `JSON string: "binary"`
| `"binary"`
|
+| **`decimal(P, S)`** | `JSON string: "decimal(<P>,<S>)"`
| `"decimal(9,2)"`,<br
/>`"decimal(9, 2)"`
|
+| **`struct`** | `JSON object: {`<br /> `"type":
"struct",`<br /> `"fields": [ {`<br /> `"id":
<field id int>,`<br /> `"name": <name string>,`<br
/> `"required": <boolean>,`<br
/> `"type": <type JSON>,`<br
/> `"doc": <comment string>,`<br
/> `"default": <JSON encoding of default value>`<br
/> `}, ...`<br /> `] }` | `{`<br
/> `"type": "struct",`<br /> `"fields": [ {`<br
/> `"id": 1,`<br /> `"name":
"id",`<br /> `"required": true,`<br
/> `"type": "uuid",`<br
/> `"default":
"0db3e2a8-9d1d-42b9-aa7b-74ebe558dceb"`<br /> `}, {`<br
/> `"id": 2,`<br /> `"name":
"data",`<br />
`"required": false,`<br /> `"type": {`<br
/> `"type": "list",`<br
/> `...`<br /> `}`<br
/> `} ]`<br />`}` |
+| **`list`** | `JSON object: {`<br /> `"type":
"list",`<br /> `"element-id": <id int>,`<br
/> `"element-required": <bool>`<br /> `"element": <type
JSON>`<br />`}`
|
`{`<br /> `"type": "list",`<br /> `"element-id": 3,`<br
/> `"element-required": true,`<br /> `"element":
"string"`<br />`}`
|
+| **`map`** | `JSON object: {`<br /> `"type":
"map",`<br /> `"key-id": <key id int>,`<br /> `"key":
<type JSON>,`<br /> `"value-id": <val id int>,`<br
/> `"value-required": <bool>`<br /> `"value": <type
JSON>`<br />`}`
|
`{`<br /> `"type": "map",`<br /> `"key-id": 4,`<br
/> `"key": "string",`<br /> `"value-id": 5,`<br
/> `"value-required": false,`<br /> `"value":
"double"`<br />`}`
|
+
+For default values, the serialization depends on the type of the corresponding
column or nested field. The mapping of types and their corresponding default
value JSON serialization is described in the following table:
+
+| Type | Json type | Example |
Note
|
+|--------------------|-------------------|----------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| **`boolean`** | **`boolean`** | `true` |
|
+| **`int`** | **`json int`** | `1` |
|
+| **`long`** | **`json long`** | `1` |
|
+| **`float`** | **`json float`** | `1.1` |
|
+| **`double`** | **`json double`** | `1.1` |
|
+| **`decimal(P,S)`** | **`string`** | `"0x3162"` |
Stores the unscaled value, as the two's-complement big-endian binary using the
minimum number of bytes, converted to a hexadecimal string prefixed by `0x`
|
+| **`date`** | **`json int`** | `19054` |
Stores days from the 1970-01-01
|
+| **`time`** | **`json long`** | `36000000000` |
Stores microseconds from midnight
|
+| **`timestamp`** | **`json long`** | `1646277378000000` |
Stores microseconds from 1970-01-01 00:00:00.000000
|
+| **`timestamptz`** | **`json long`** | `1646277378000000` |
Stores microseconds from 1970-01-01 00:00:00.000000 UTC
|
+| **`string`** | **`string`** | `"foo"` |
|
+| **`uuid`** | **`string`** |
`"eb26bdb1-a1d8-4aa6-990e-da940875492c"` | Stores the lowercase uuid string
|
+| **`fixed(L)`** | **`string`** | `"0x3162"` |
Stored as a hexadecimal byte literal string, prefixex by `0x`
|
+| **`binary`** | **`string`** | `"0x3162"` |
Stored as a hexadecimal byte literal string, prefixex by `0x`
|
+| **`struct`** | **`object`** | `{"a": 1, "foo": "bar"}` |
Use a JSON map to represent struct data, the keys are the nested fields' names
in the struct schema, and the values are value literals of corresponding
fields' type
|
Review comment:
> This requires a fairly complicated process to rewrite the default
value when the schema changes because it uses field names instead of field IDs.
Have you considered other representations, like a list of fields: `[
{"field-id": 5, "value": "s"}, ... ]`?
I think you are right about using field id to better track fields in terms
of schema evolution. do you think array and map also need to be encoded this
way (using field-id instead of name)? My feeling is they are unnecessary
because array and map can't have schema evolution themselves anyway?
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