将 CSV 文件(包含空字符串和重复项)导入 DynamoDB [英] Importing a CSV file (with empty strings and duplicates) into DynamoDB

问题描述

我有一个 CSV 文件，我正在尝试将其导入 Amazon DynamoDB.所以我把它上传到 S3，建立一个 EMR 集群，然后创建一个像这样的外部表:

I have a CSV file that I'm trying to import to Amazon DynamoDB. So I upload it to S3, set up a EMR cluster, and create an external table like this:

hive> CREATE EXTERNAL TABLE s3_table_myitems (colA BIGINT, colB STRING, colC STRING, colD DOUBLE, colE DOUBLE, colF STRING, colG STRING)
    ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.OpenCSVSerde'
    WITH SERDEPROPERTIES ('serialization.null.format'='""')
    STORED AS TEXTFILE
    LOCATION 's3://bucketname/dirname/'
    TBLPROPERTIES ('skip.header.line.count'='1');

CSV 中的任何列都可能为空，但 DynamoDB 无法处理空字符串(com.amazonaws.AmazonServiceException:一个或多个参数值无效:AttributeValue 可能不包含空字符串").

Any of the columns in the CSV may be empty, but DynamoDB can't deal with empty strings ("com.amazonaws.AmazonServiceException: One or more parameter values were invalid: An AttributeValue may not contain an empty string").

这就是亚马逊所说的:

我们将考虑这个可选的忽略空字符串"行为未来的版本.... 作为一种解决方法，您可以... 转换为空属性值转换为 NULL.例如，您可以……使用更复杂的SELECT 表达式将空字符串转换为其他内容，包括将它们设置为 NULL.

We will consider this optional "ignore empty string" behavior in a future release. … As a workaround, you could … transform empty attribute values into NULLs. For example, you can … use a more complex SELECT expression to turn empty strings into something else, including setting them to NULL.

所以这就是我想出的，但它看起来很丑:

So this is what I came up with, but it looks ugly:

hive> INSERT INTO TABLE ddb_tbl_ingredients
    SELECT
    regexp_replace(colA, '^$', 'NULL'),
    regexp_replace(colB, '^$', 'NULL'),
    regexp_replace(colC, '^$', 'NULL'),
    regexp_replace(colD, '^$', 'NULL'),
    regexp_replace(colE, '^$', 'NULL'),
    regexp_replace(colF, '^$', 'NULL'),
    regexp_replace(colG, '^$', 'NULL')
    FROM s3_table_ingredients;

对于整体问题是否有更好的解决方案(缺少对 CSV 的预处理)，或者至少有更好的 SELECT 语法?

Is there a better solution to the overall problem (short of pre-processing the CSV), or at least a better SELECT syntax?

编辑:我最终也不得不处理重复项(com.amazonaws.AmazonServiceException:提供的项目键列表包含重复项").

Edit: I ended up having to deal with duplicates as well ("com.amazonaws.AmazonServiceException: Provided list of item keys contains duplicates").

为了后代，这是我的完整流程.我很想听到更好的方法来做到这一点，无论是为了美观还是为了性能.任务看似简单(将 CSV 文件导入 DynamoDB")，但到目前为止已经花费了几个小时:P

For posterity, here's my complete flow. I'd love to hear of a better way of doing this, both for aesthetics and for performance. The task is seemingly simple ("importing a CSV file into DynamoDB") but coming up with this has taken hours so far :P

# source
hive> CREATE EXTERNAL TABLE s3_table_myitems (colA STRING, colB STRING, colC DOUBLE, colD DOUBLE, colE STRING, colF STRING)
    ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.OpenCSVSerde'
    WITH SERDEPROPERTIES ('serialization.null.format'='""')
    STORED AS TEXTFILE
    LOCATION 's3://bucketname/dirname/'
    TBLPROPERTIES ('skip.header.line.count'='1');

# destination
hive> CREATE EXTERNAL TABLE ddb_tbl_myitems (colA STRING, colB STRING, colC DOUBLE, colD DOUBLE, colE STRING, colF STRING)
    STORED BY 'org.apache.hadoop.hive.dynamodb.DynamoDBStorageHandler'
    TBLPROPERTIES ("dynamodb.table.name" = "myitems",
        "dynamodb.column.mapping" = "colA:colA,colB:colB,colC:colC,colD:colD,colE:colE,colF:colF");

# remove dupes - http://stackoverflow.com/a/34165762/594211
hive> CREATE TABLE tbl_myitems_deduped AS
    SELECT colA, min(colB) AS colB, min(colC) AS colC, min(colD) AS colD, min(colE) AS colE, min(colF) AS colF
    FROM (SELECT colA, colB, colC, colD, unit, colF, rank() OVER
        (PARTITION BY colA ORDER BY colB, colC, colD, colE, colF)
        AS col_rank FROM s3_table_myitems) t
    WHERE t.col_rank = 1
    GROUP BY colA;

# replace empty strings with placeholder 'NULL'
hive> CREATE TABLE tbl_myitems_noempty AS
    SELECT colA,
    regexp_replace(colB, '^$', 'NULL') AS colB,
    regexp_replace(colC, '^$', 'NULL') AS colC,
    regexp_replace(colD, '^$', 'NULL') AS colD,
    regexp_replace(colE, '^$', 'NULL') AS colE,
    regexp_replace(colF, '^$', 'NULL') AS colF
    FROM tbl_myitems_deduped
    WHERE LENGTH(colA) > 0;

# ...other preprocessing here...

# insert to DB
hive> INSERT INTO TABLE ddb_tbl_myitems
    SELECT * FROM tbl_myitems_noempty;

注意:colA 是分区键.

推荐答案

您可以在 create table 语句中添加额外的表属性，将任何指定的字符视为空值.

You can add additional table properties to your create table statement that will treat any specified character as a null value.

TBLPROPERTIES('serialization.null.format'='');

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