Improve performance

Compression using gzip

An easy and convenient way to reduce the bandwidth needed for each request is to enable gzip compression. Although this requires additional CPU time to uncompress the results, the trade-off with network costs usually makes it very worthwhile.

In order to receive a gzip-encoded response you must do two things: Set an Accept-Encoding header, and modify your user agent to contain the string gzip. Here is an example of properly formed HTTP headers for enabling gzip compression:

Accept-Encoding: gzip
User-Agent: my program (gzip)

Working with partial resources

Another way to improve the performance of your API calls is by sending and receiving only the portion of the data that you're interested in. This lets your application avoid transferring, parsing, and storing unneeded fields, so it can use resources including network, CPU, and memory more efficiently.

There are two types of partial requests:

• Partial response: A request where you specify which fields to include in the response (use the fields request parameter).
• Patch: An update request where you send only the fields you want to change (use the PATCH HTTP verb).

More details on making partial requests are provided in the following sections.

Partial response

By default, the server sends back the full representation of a resource after processing requests. For better performance, you can ask the server to send only the fields you really need and get a partial response instead.

To request a partial response, use the fields request parameter to specify the fields you want returned. You can use this parameter with any request that returns response data.

Note that the fields parameter only affects the response data; it does not affect the data that you need to send, if any. To reduce the amount of data you send when modifying resources, use a patch request.

Example

The following example shows the use of the fields parameter with a generic (fictional) "Demo" API.

Simple request: This HTTP GET request omits the fields parameter and returns the full resource.

https://www.googleapis.com/demo/v1

Full resource response: The full resource data includes the following fields, along with many others that have been omitted for brevity.

{
  "kind": "demo",
  ...
  "items": [
  {
    "title": "First title",
    "comment": "First comment.",
    "characteristics": {
      "length": "short",
      "accuracy": "high",
      "followers": ["Jo", "Will"],
    },
    "status": "active",
    ...
  },
  {
    "title": "Second title",
    "comment": "Second comment.",
    "characteristics": {
      "length": "long",
      "accuracy": "medium"
      "followers": [ ],
    },
    "status": "pending",
    ...
  },
  ...
  ]
}

Request for a partial response: The following request for this same resource uses the fields parameter to significantly reduce the amount of data returned.

https://www.googleapis.com/demo/v1?fields=kind,items(title,characteristics/length)

Partial response: In response to the request above, the server sends back a response that contains only the kind information along with a pared-down items array that includes only HTML title and length characteristic information in each item.

200 OK

{
  "kind": "demo",
  "items": [{
    "title": "First title",
    "characteristics": {
      "length": "short"
    }
  }, {
    "title": "Second title",
    "characteristics": {
      "length": "long"
    }
  },
  ...
  ]
}

Note that the response is a JSON object that includes only the selected fields and their enclosing parent objects.

Details on how to format the fields parameter is covered next, followed by more details about what exactly gets returned in the response.

Fields parameter syntax summary

The format of the fields request parameter value is loosely based on XPath syntax. The supported syntax is summarized below, and additional examples are provided in the following section.

• Use a comma-separated list to select multiple fields.
• Use a/b to select a field b that is nested within field a; use a/b/c to select a field c nested within b.
  

  Exception: For API responses that use "data" wrappers, where the response is nested within a data object that looks like data: { ... }, do not include "data" in the fields specification. Including the data object with a fields specification like data/a/b causes an error. Instead, just use a fields specification like a/b.

• Use a sub-selector to request a set of specific sub-fields of arrays or objects by placing expressions in parentheses "( )".

  For example: fields=items(id,author/email) returns only the item ID and author's email for each element in the items array. You can also specify a single sub-field, where fields=items(id) is equivalent to fields=items/id.

• Use wildcards in field selections, if needed.

  For example: fields=items/pagemap/* selects all objects in a pagemap.

More examples of using the fields parameter

The examples below include descriptions of how the fields parameter value affects the response.

Note: As with all query parameter values, the fields parameter value must be URL encoded. For better readability, the examples in this document omit the encoding.

Identify the fields you want returned, or make field selections.

The fields request parameter value is a comma-separated list of fields, and each field is specified relative to the root of the response. Thus, if you are performing a list operation, the response is a collection, and it generally includes an array of resources. If you are performing an operation that returns a single resource, fields are specified relative to that resource. If the field you select is (or is part of) an array, the server returns the selected portion of all elements in the array.

Here are some collection-level examples:

Examples	Effect
items	Returns all elements in the items array, including all fields in each element, but no other fields.
etag,items	Returns both the etag field and all elements in the items array.
items/title	Returns only the title field for all elements in the items array. Whenever a nested field is returned, the response includes the enclosing parent objects. The parent fields do not include any other child fields unless they are also selected explicitly.
context/facets/label	Returns only the label field for all members of the facets array, which is itself nested under the context object.
items/pagemap/*/title	For each element in the items array, returns only the title field (if present) of all objects that are children of pagemap.

Here are some resource-level examples:

Examples	Effect
title	Returns the title field of the requested resource.
author/uri	Returns the uri sub-field of the author object in the requested resource.
links/*/href	Returns the href field of all objects that are children of links.

Request only parts of specific fields using sub-selections.

By default, if your request specifies particular fields, the server returns the objects or array elements in their entirety. You can specify a response that includes only certain sub-fields. You do this using "( )" sub-selection syntax, as in the example below.

Example	Effect
items(title,author/uri)	Returns only the values of the title and author's uri for each element in the items array.

Handling partial responses

After a server processes a valid request that includes the fields query parameter, it sends back an HTTP 200 OK status code, along with the requested data. If the fields query parameter has an error or is otherwise invalid, the server returns an HTTP 400 Bad Request status code, along with an error message telling the user what was wrong with their fields selection (for example, "Invalid field selection a/b").

Here is the partial response example shown in the introductory section above. The request uses the fields parameter to specify which fields to return.

https://www.googleapis.com/demo/v1?fields=kind,items(title,characteristics/length)

The partial response looks like this:

200 OK

{
  "kind": "demo",
  "items": [{
    "title": "First title",
    "characteristics": {
      "length": "short"
    }
  }, {
    "title": "Second title",
    "characteristics": {
      "length": "long"
    }
  },
  ...
  ]
}

Note: For APIs that support query parameters for data pagination (maxResults and nextPageToken, for example), use those parameters to reduce the results of each query to a manageable size. Otherwise, the performance gains possible with partial response might not be realized.

Patch (partial update)

You can also avoid sending unnecessary data when modifying resources. To send updated data only for the specific fields that you’re changing, use the HTTP PATCH verb. The patch semantics described in this document are different (and simpler) than they were for the older, GData implementation of partial update.

The short example below shows how using patch minimizes the data you need to send to make a small update.

Example

This example shows a simple patch request to update only the title of a generic (fictional) "Demo" API resource. The resource also has a comment, a set of characteristics, status, and many other fields, but this request only sends the title field, since that's the only field being modified:

PATCH https://www.googleapis.com/demo/v1/324
Authorization: Bearer your_auth_token
Content-Type: application/json

{
  "title": "New title"
}

Response:

200 OK

{
  "title": "New title",
  "comment": "First comment.",
  "characteristics": {
    "length": "short",
    "accuracy": "high",
    "followers": ["Jo", "Will"],
  },
  "status": "active",
  ...
}

The server returns a 200 OK status code, along with the full representation of the updated resource. Since only the title field was included in the patch request, that's the only value that is different from before.

Note: If you use the partial response fields parameter in combination with patch, you can increase the efficiency of your update requests even further. A patch request only reduces the size of the request. A partial response reduces the size of the response. So to reduce the amount of data sent in both directions, use a patch request with the fields parameter.

Semantics of a patch request

The body of the patch request includes only the resource fields you want to modify. When you specify a field, you must include any enclosing parent objects, just as the enclosing parents are returned with a partial response. The modified data you send is merged into the data for the parent object, if there is one.

• Add: To add a field that doesn't already exist, specify the new field and its value.
• Modify: To change the value of an existing field, specify the field and set it to the new value.
  
• Delete: To delete a field, specify the field and set it to null. For example, "comment": null. You can also delete an entire object (if it is mutable) by setting it to null. If you are using the Java API Client Library, use Data.NULL_STRING instead; for details, see JSON null.

Note about arrays: Patch requests that contain arrays replace the existing array with the one you provide. You cannot modify, add, or delete items in an array in a piecemeal fashion.

Using patch in a read-modify-write cycle

It can be a useful practice to start by retrieving a partial response with the data you want to modify. This is especially important for resources that use ETags, since you must provide the current ETag value in the If-Match HTTP header in order to update the resource successfully. After you get the data, you can then modify the values you want to change and send the modified partial representation back with a patch request. Here is an example that assumes the Demo resource uses ETags:

GET https://www.googleapis.com/demo/v1/324?fields=etag,title,comment,characteristics
Authorization: Bearer your_auth_token

This is the partial response:

200 OK

{
  "etag": "ETagString"
  "title": "New title"
  "comment": "First comment.",
  "characteristics": {
    "length": "short",
    "level": "5",
    "followers": ["Jo", "Will"],
  }
}

The following patch request is based on that response. As shown below, it also uses the fields parameter to limit the data returned in the patch response:

PATCH https://www.googleapis.com/demo/v1/324?fields=etag,title,comment,characteristics
Authorization: Bearer your_auth_token
Content-Type: application/json
If-Match: "ETagString"

{
  "etag": "ETagString"
  "title": "",                  /* Clear the value of the title by setting it to the empty string. */
  "comment": null,              /* Delete the comment by replacing its value with null. */
  "characteristics": {
    "length": "short",
    "level": "10",              /* Modify the level value. */
    "followers": ["Jo", "Liz"], /* Replace the followers array to delete Will and add Liz. */
    "accuracy": "high"          /* Add a new characteristic. */
  },
}

The server responds with a 200 OK HTTP status code, and the partial representation of the updated resource:

200 OK

{
  "etag": "newETagString"
  "title": "",                 /* Title is cleared; deleted comment field is missing. */
  "characteristics": {
    "length": "short",
    "level": "10",             /* Value is updated.*/
    "followers": ["Jo" "Liz"], /* New follower Liz is present; deleted Will is missing. */
    "accuracy": "high"         /* New characteristic is present. */
  }
}

Constructing a patch request directly

For some patch requests, you need to base them on the data you previously retrieved. For example, if you want to add an item to an array and don't want to lose any of the existing array elements, you must get the existing data first. Similarly, if an API uses ETags, you need to send the previous ETag value with your request in order to update the resource successfully.

Note: You can use an "If-Match: *" HTTP header to force a patch to go through when ETags are in use.  If you do this, you don't need to do the read before the write.

For other situations, however, you can construct the patch request directly, without first retrieving the existing data. For example, you can easily set up a patch request that updates a field to a new value or adds a new field. Here is an example:

PATCH https://www.googleapis.com/demo/v1/324?fields=comment,characteristics
Authorization: Bearer your_auth_token
Content-Type: application/json

{
  "comment": "A new comment",
  "characteristics": {
    "volume": "loud",
    "accuracy": null
  }
}

With this request, if the comment field has an existing value, the new value overwrites it; otherwise it is set to the new value. Similarly, if there was a volume characteristic, its value is overwritten; if not, it is created. The accuracy field, if set, is removed.

Handling the response to a patch

After processing a valid patch request, the API returns a 200 OK HTTP response code along with the complete representation of the modified resource. If ETags are used by the API, the server updates ETag values when it successfully processes a patch request, just as it does with PUT.

The patch request returns the entire resource representation unless you use the fields parameter to reduce the amount of data it returns.

If a patch request results in a new resource state that is syntactically or semantically invalid, the server returns a 400 Bad Request or 422 Unprocessable Entity HTTP status code, and the resource state remains unchanged. For example, if you attempt to delete the value for a required field, the server returns an error.

Alternate notation when PATCH HTTP verb is not supported

If your firewall does not allow HTTP PATCH requests, then do an HTTP POST request and set the override header to PATCH, as shown below:

POST https://www.googleapis.com/...
X-HTTP-Method-Override: PATCH
...

Difference between patch and update

In practice, when you send data for an update request that uses the HTTP PUT verb, you only need to send those fields which are either required or optional; if you send values for fields that are set by the server, they are ignored. Although this might seem like another way to do a partial update, this approach has some limitations. With updates that use the HTTP PUT verb, the request fails if you don't supply required parameters, and it clears previously set data if you don't supply optional parameters.

It's much safer to use patch for this reason. You only supply data for the fields you want to change; fields that you omit are not cleared. The only exception to this rule occurs with repeating elements or arrays: If you omit all of them, they stay just as they are; if you provide any of them, the whole set is replaced with the set that you provide.

Overview

Each HTTP connection your client makes results in a certain amount of overhead. The Google Drive API supports batching, to allow your client to put several API calls into a single HTTP request.

Examples of situations when you might want to use batching:

• Retrieving metadata for a large number of files.
• Updating metadata or properties in bulk.
• Changing permissions for a large number of files, such as adding a new user or group.
• Synchronizing local client data for the first time or after being offline for an extended time.

In each case, instead of sending each call separately, you can group them together into a single HTTP request. All the inner requests must go to the same Google API.

You're limited to 100 calls in a single batch request. If you must make more calls than that, use multiple batch requests.

Note: The batch system for the Google Drive API uses the same syntax as the OData batch processing system, but the semantics differ.

Additional constraints include:

• Batch requests with more than 100 calls might cause an error.
• There's an 8,000 character limit on the length of the URL for each inner request.
• Google Drive doesn't support batch operations for media, either for upload or download, or for exporting files.

Batch details

A batch request consists of multiple API calls combined into one HTTP request, which can be sent to the batchPath specified in the API discovery document. The default path is /batch/api_name/api_version. This section describes the batch syntax in detail; later, there's an example.

Note: A set of n requests batched together counts toward your usage limit as n requests, not as one request. The batch request is separated into a set of requests before processing.

Format of a batch request

A batch request is a single standard HTTP request containing multiple Google Drive API calls, using the multipart/mixed content type. Within that main HTTP request, each of the parts contains a nested HTTP request.

Each part begins with its own Content-Type: application/http HTTP header. It can also have an optional Content-ID header. However, the part headers are just there to mark the beginning of the part; they're separate from the nested request. After the server unwraps the batch request into separate requests, the part headers are ignored.

The body of each part is a complete HTTP request, with its own verb, URL, headers, and body. The HTTP request must only contain the path portion of the URL; full URLs are not allowed in batch requests.

The HTTP headers for the outer batch request, except for the Content- headers such as Content-Type, apply to every request in the batch. If you specify a given HTTP header in both the outer request and an individual call, then the individual call header's value overrides the outer batch request header's value. The headers for an individual call apply only to that call.

For example, if you provide an Authorization header for a specific call, then that header applies only to that call. If you provide an Authorization header for the outer request, then that header applies to all of the individual calls unless they override it with Authorization headers of their own.

When the server receives the batched request, it applies the outer request's query parameters and headers (as appropriate) to each part, and then treats each part as if it were a separate HTTP request.

Response to a batch request

The server's response is a single standard HTTP response with a multipart/mixed content type; each part is the response to one of the requests in the batched request, in the same order as the requests.

Like the parts in the request, each response part contains a complete HTTP response, including a status code, headers, and body. And like the parts in the request, each response part is preceded by a Content-Type header that marks the beginning of the part.

If a given part of the request had a Content-ID header, then the corresponding part of the response has a matching Content-ID header, with the original value preceded by the string response-, as shown in the following example.

Note: The server might perform your calls in any order. Don't count on their being executed in the order in which you specified them. If you want to ensure that two calls occur in a given order, you can't send them in a single request; instead, send the first one by itself, then wait for the response to the first one before sending the second one.

Example

The following example shows the use of batching with the Google Drive API.

Example batch request

POST https://www.googleapis.com/batch/drive/v3
Accept-Encoding: gzip
User-Agent: Google-HTTP-Java-Client/1.20.0 (gzip)
Content-Type: multipart/mixed; boundary=END_OF_PART
Content-Length: 963


--END_OF_PART
Content-Length: 337
Content-Type: application/http
content-id: 1
content-transfer-encoding: binary

POST https://www.googleapis.com/drive/v3/files/fileId/permissions?fields=id
Authorization: Bearer authorization_token
Content-Length: 70
Content-Type: application/json; charset=UTF-8

{
  "emailAddress":"example@appsrocks.com",
  "role":"writer",
  "type":"user"
}
--END_OF_PART
Content-Length: 353
Content-Type: application/http
content-id: 2
content-transfer-encoding: binary

POST https://www.googleapis.com/drive/v3/files/fileId/permissions?fields=id&sendNotificationEmail=false
Authorization: Bearer authorization_token
Content-Length: 58
Content-Type: application/json; charset=UTF-8

{
   "domain":"appsrocks.com",
   "role":"reader",
   "type":"domain"
}
--END_OF_PART--

Example batch response

This is the response to the example request in the previous section.

HTTP/1.1 200 OK
Alt-Svc: quic=":443"; p="1"; ma=604800
Server: GSE
Alternate-Protocol: 443:quic,p=1
X-Frame-Options: SAMEORIGIN
Content-Encoding: gzip
X-XSS-Protection: 1; mode=block
Content-Type: multipart/mixed; boundary=batch_6VIxXCQbJoQ_AATxy_GgFUk
Transfer-Encoding: chunked
X-Content-Type-Options: nosniff
Date: Fri, 13 Nov 2015 19:28:59 GMT
Cache-Control: private, max-age=0
Vary: X-Origin
Vary: Origin
Expires: Fri, 13 Nov 2015 19:28:59 GMT


--batch_6VIxXCQbJoQ_AATxy_GgFUk
Content-Type: application/http
Content-ID: response-1

HTTP/1.1 200 OK
Content-Type: application/json; charset=UTF-8
Date: Fri, 13 Nov 2015 19:28:59 GMT
Expires: Fri, 13 Nov 2015 19:28:59 GMT
Cache-Control: private, max-age=0
Content-Length: 35

{
 "id": "12218244892818058021i"
}

--batch_6VIxXCQbJoQ_AATxy_GgFUk
Content-Type: application/http
Content-ID: response-2

HTTP/1.1 200 OK
Content-Type: application/json; charset=UTF-8
Date: Fri, 13 Nov 2015 19:28:59 GMT
Expires: Fri, 13 Nov 2015 19:28:59 GMT
Cache-Control: private, max-age=0
Content-Length: 35

{
 "id": "04109509152946699072k"
}

--batch_6VIxXCQbJoQ_AATxy_GgFUk--