batchWriteItem with the same partition key - php

Question

I have a dynamodb table with a partition key id and a sort key value
Now I want to run batchWriteItem to insert multiple items with the same partition key and a different sort key but it only inserts the last item:
$response = $dynamoDb->batchWriteItem([
'RequestItems' => [
'mytable' => [
[
'PutRequest' => [
'Item' => [
'id' => array('S' => '123abc'),
'value' => array('N' => '1'),
],
'Item' => [
'id' => array('S' => '123abc'),
'value' => array('N' => '2'),
],
'Item' => [
'id' => array('S' => '123abc'),
'value' => array('N' => '3'),
]],
],
],
],
]);
With this code only the item with the value 3 gets inserted
"Items": [
{
"id": {
"S": "123abc"
},
"value": {
"N": "3"
}
}
],
Is there something wrong with the code or something I didn't consider?
It perfectly works when doing single requests:
$response = $dynamoDb->putItem(array(
'TableName' => 'mytable',
'Item' => array(
'id' => array('S' => '123abc'),
'value' => array('N' => '1'),
),
));
$response = $dynamoDb->putItem(array(
'TableName' => 'mytable',
'Item' => array(
'id' => array('S' => '123abc'),
'value' => array('N' => '2'),
),
));
$response = $dynamoDb->putItem(array(
'TableName' => 'mytable',
'Item' => array(
'id' => array('S' => '123abc'),
'value' => array('N' => '3'),
),
));
Is there any performence difference between batchWriteItem or doing 3 single putItem reuests in sequence?

Answer 1

You are using incorrect syntax for batchWrite, try following
$response = $dynamoDb->batchWriteItem([
'RequestItems' => [
'mytable' => [
[
'PutRequest' => [
'Item' => [
'id' => array('S' => '123abc'),
'value' => array('N' => '1'),
]
],
'PutRequest' => [ ///Entire PutRequest array need to be repeated not just item array///
'Item' => [
'id' => array('S' => '123abc'),
'value' => array('N' => '2'),
]
],
],
],
],
]);
Apart from that, the difference between single insert and multiple inserts would be the call to connect with DynamoDB, in batchPut you will send entire array at once whereas in single insert it will connect to DB each time it tries to perform any operation.
In general, you can use Batch to process things faster.
Here is the refernce link for batchWrite syntax
Hope that helps.