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    Object Storage Service:CreateSelectObjectMeta

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    Object Storage Service:CreateSelectObjectMeta

    Last Updated:Jun 17, 2026

    Obtains metadata about a CSV or JSON object, including the total number of rows, splits, and columns (CSV only). Each object consists of data blocks, where each block corresponds to a split of consecutive rows. If the metadata does not already exist, the entire object is scanned and the results are recorded for subsequent calls without rescanning.

    Usage notes

    • To call the CreateSelectObjectMeta operation, you must have write permissions on the object.

    • If the operation is successful, HTTP status code 200 is returned. If the object is not a valid CSV or JSON LINES object, or if the specified delimiter does not match existing CSV objects, HTTP status code 400 is returned.

    Syntax

    This operation uses the following request syntax for CSV and JSON objects.

    • Request syntax for CSV objects

      POST  /samplecsv?x-oss-process=csv/meta
<CsvMetaRequest>
    <InputSerialization>
        <CompressionType>None</CompressionType>
        <CSV>
            <RecordDelimiter>Base64-encoded character</RecordDelimiter>
            <FieldDelimiter>Base64-encoded character</FieldDelimiter>
            <QuoteCharacter>Base64-encoded character</QuoteCharacter>
        </CSV>
    </InputSerialization>
    <OverwriteIfExists>false|true</OverwriteIfExists>
</CsvMetaRequest>

    • Request syntax for JSON objects

      POST  /samplecsv?x-oss-process=json/meta
<JsonMetaRequest>
    <InputSerialization>
        <CompressionType>None</CompressionType>
        <JSON>
            <Type>LINES</Type>
        </JSON>
    </InputSerialization>
    <OverwriteIfExists>false|true</OverwriteIfExists>
</JsonMetaRequest>

    Request elements

    Element

    Type

    Description

    CsvMetaRequest

    Container

    The container for the CreateSelectObjectMeta request for CSV objects.

    Child nodes: InputSerialization

    Parent nodes: none

    JsonMetaRequest

    Container

    The container for the CreateSelectObjectMeta request for JSON objects.

    Child nodes: InputSerialization

    Parent nodes: none

    InputSerialization

    Container

    Optional. The input serialization parameters.

    Child nodes: CompressionType, CSV, and JSON

    Parent nodes: CsvMetaRequest and JsonMetaRequest

    OverwriteIfExists

    bool

    Optional. Specifies whether to recalculate the SelectMeta and overwrite the existing data. A value of false returns the existing result directly. Default value: false.

    Child nodes: none

    Parent nodes: CsvMetaRequest and JsonMetaRequest

    CompressionType

    Enumeration

    Optional. The compression type of the object. Valid value: None.

    Child nodes: none

    Parent nodes: InputSerialization

    RecordDelimiter

    String

    Optional. The Base64-encoded line feed used to separate rows in the CSV object. Default value: \n. Before encoding, the value must be an ANSI value of up to two characters in length. For example, \n indicates a line feed in Java.

    Child nodes: none

    Parent nodes: CSV

    FieldDelimiter

    String

    Optional. The Base64-encoded delimiter used to separate values in the CSV object. Default value: ,.

    Before encoding, the value must be an ANSI value of one character in length. For example, , indicates a comma in Java.

    Child nodes: none

    Parent nodes: CSV (input and output)

    QuoteCharacter

    String

    Optional. The Base64-encoded quote character for the CSV object. Default value: \". In a CSV object, line feeds and column delimiters enclosed in quotation marks are treated as literal characters. Before encoding, the value must be an ANSI value of one character in length. For example, \" indicates a quotation mark in Java.

    Child nodes: none

    Parent nodes: CSV (input)

    CSV

    Container

    The input format of the CSV object.

    Child nodes: RecordDelimiter, FieldDelimiter, and QuoteCharacter

    Parent nodes: InputSerialization

    JSON

    Container

    The input format of the JSON object.

    Child nodes: Type

    Parent nodes: InputSerialization

    Type

    Enumeration

    The type of the JSON object.

    Valid value: LINES.

    Response headers

    Like SelectObject, CreateSelectObjectMeta returns results as frames.

    Frame type

    Value

    Payload format

    Description

    Meta End Frame (CSV)

    8388614

    offset | total scanned bytes | status| splits count | rows count | columns count | error message

    <-8 bytes><------8 bytes------><--4bytes><--4 bytes--><--8 bytes><--4 bytes---><variable size>

    Reports the final state of a CreateSelectObjectMeta operation.

    • offset: an 8-bit integer that indicates the offset when scanning is complete.

    • total scanned bytes: an 8-bit integer that indicates the size of the scanned data.

    • status: a 4-bit integer that indicates the final state of the operation.

    • splits_count: a 4-bit integer that indicates the total number of splits.

    • rows_count: an 8-bit integer that indicates the total number of rows.

    • cols_count: a 4-bit integer that indicates the total number of columns.

    • error_message: the detailed error message. If no errors occur, this value is null.

    Meta End Frame (JSON)

    8388615

    offset | total scanned bytes | status| splits count | rows count | error message

    <-8 bytes><------8 bytes------><--4bytes><--4 bytes--><--8 bytes><variable size>

    Reports the final state of a CreateSelectObjectMeta operation.

    • offset: an 8-bit integer that indicates the offset when scanning is complete.

    • total scanned bytes: an 8-bit integer that indicates the size of the scanned data.

    • status: a 4-bit integer that indicates the final state of the operation.

    • splits_count: a 4-bit integer that indicates the total number of splits.

    • rows_count: an 8-bit integer that indicates the total number of rows.

    • error_message: the detailed error message. If no errors occur, this value is null.

    Sample requests

    The following examples show how to call CreateSelectObjectMeta for CSV and JSON objects:

    • Sample requests for CSV objects

      POST /oss-select/bigcsv_normal.csv?x-oss-process=csv%2Fmeta HTTP/1.1
Date: Fri, 25 May 2018 23:06:41 GMT
Content-Type:
Authorization: OSS4-HMAC-SHA256 Credential=LTAI********************/20250417/cn-hangzhou/oss/aliyun_v4_request,AdditionalHeaders=content-length,Signature=a7c3554c729d71929e0b84489addee6b2e8d5cb48595adfc51868c299c0c218e
User-Agent: aliyun-sdk-dotnet/2.8.0.0(windows 16.7/16.7.0.0/x86;4.0.30319.42000)
Content-Length: 309
Expect: 100-continue
Connection: keep-alive
Host: Host
<?xml version="1.0"?>
<CsvMetaRequest>
    <InputSerialization>
        <CSV>
            <RecordDelimiter>Cg==</RecordDelimiter>
            <FieldDelimiter>LA==</FieldDelimiter>
            <QuoteCharacter>Ig==</QuoteCharacter>
        </CSV>
    </InputSerialization>
    <OverwriteIfExisting>false</OverwriteIfExisting>
</CsvMetaRequest>

    • Sample requests for JSON objects

      POST /oss-select/sample.json?x-oss-process=json%2Fmeta HTTP/1.1
Date: Fri, 25 May 2018 23:06:41 GMT
Content-Type:
Authorization: OSS4-HMAC-SHA256 Credential=LTAI********************/20250417/cn-hangzhou/oss/aliyun_v4_request,AdditionalHeaders=content-length,Signature=a7c3554c729d71929e0b84489addee6b2e8d5cb48595adfc51868c299c0c218e
User-Agent: aliyun-sdk-dotnet/2.8.0.0(windows 16.7/16.7.0.0/x86;4.0.30319.42000)
Content-Length: 309
Expect: 100-continue
Connection: keep-alive
Host: Host
<?xml version="1.0"?>
<JsonMetaRequest>
    <InputSerialization>
        <JSON>
            <Type>LINES</Type>
        </JSON>
    </InputSerialization>
    <OverwriteIfExisting>false</OverwriteIfExisting>
</JsonMetaRequest>

    ossutil

    For more information about the ossutil command for the CreateSelectObjectMeta operation, see create-select-object-meta.