Index: tools/telemetry/third_party/gsutil/gslib/addlhelp/versions.py |
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-# -*- coding: utf-8 -*- |
-# Copyright 2012 Google Inc. All Rights Reserved. |
-# |
-# Licensed under the Apache License, Version 2.0 (the "License"); |
-# you may not use this file except in compliance with the License. |
-# You may obtain a copy of the License at |
-# |
-# http://www.apache.org/licenses/LICENSE-2.0 |
-# |
-# Unless required by applicable law or agreed to in writing, software |
-# distributed under the License is distributed on an "AS IS" BASIS, |
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
-# See the License for the specific language governing permissions and |
-# limitations under the License. |
-"""Additional help about object versioning.""" |
- |
-from __future__ import absolute_import |
- |
-from gslib.help_provider import HelpProvider |
- |
-_DETAILED_HELP_TEXT = (""" |
-<B>OVERVIEW</B> |
- Versioning-enabled buckets maintain an archive of objects, providing a way to |
- un-delete data that you accidentally deleted, or to retrieve older versions of |
- your data. You can turn versioning on or off for a bucket at any time. Turning |
- versioning off leaves existing object versions in place, and simply causes the |
- bucket to stop accumulating new object versions. In this case, if you upload |
- to an existing object the current version is overwritten instead of creating |
- a new version. |
- |
- Regardless of whether you have enabled versioning on a bucket, every object |
- has two associated positive integer fields: |
- |
- - the generation, which is updated when the content of an object is |
- overwritten. |
- - the metageneration, which identifies the metadata generation. It starts |
- at 1; is updated every time the metadata (e.g., ACL or Content-Type) for a |
- given content generation is updated; and gets reset when the generation |
- number changes. |
- |
- Of these two integers, only the generation is used when working with versioned |
- data. Both generation and metageneration can be used with concurrency control |
- (discussed in a later section). |
- |
- To work with object versioning in gsutil, you can use a flavor of storage URIs |
- that that embed the object generation, which we refer to as version-specific |
- URIs. For example, the version-less object URI: |
- |
- gs://bucket/object |
- |
- might have have two versions, with these version-specific URIs: |
- |
- gs://bucket/object#1360383693690000 |
- gs://bucket/object#1360383802725000 |
- |
- The following sections discuss how to work with versioning and concurrency |
- control. |
- |
- |
-<B>OBJECT VERSIONING</B> |
- You can view, enable, and disable object versioning on a bucket using |
- the 'versioning get' and 'versioning set' commands. For example: |
- |
- gsutil versioning set on gs://bucket |
- |
- will enable versioning for the named bucket. See 'gsutil help versioning' |
- for additional details. |
- |
- To see all object versions in a versioning-enabled bucket along with |
- their generation.metageneration information, use gsutil ls -a: |
- |
- gsutil ls -a gs://bucket |
- |
- You can also specify particular objects for which you want to find the |
- version-specific URI(s), or you can use wildcards: |
- |
- gsutil ls -a gs://bucket/object1 gs://bucket/images/*.jpg |
- |
- The generation values form a monotonically increasing sequence as you create |
- additional object versions. Because of this, the latest object version is |
- always the last one listed in the gsutil ls output for a particular object. |
- For example, if a bucket contains these three versions of gs://bucket/object: |
- |
- gs://bucket/object#1360035307075000 |
- gs://bucket/object#1360101007329000 |
- gs://bucket/object#1360102216114000 |
- |
- then gs://bucket/object#1360102216114000 is the latest version and |
- gs://bucket/object#1360035307075000 is the oldest available version. |
- |
- If you specify version-less URIs with gsutil, you will operate on the |
- latest not-deleted version of an object, for example: |
- |
- gsutil cp gs://bucket/object ./dir |
- |
- or: |
- |
- gsutil rm gs://bucket/object |
- |
- To operate on a specific object version, use a version-specific URI. |
- For example, suppose the output of the above gsutil ls -a command is: |
- |
- gs://bucket/object#1360035307075000 |
- gs://bucket/object#1360101007329000 |
- |
- In this case, the command: |
- |
- gsutil cp gs://bucket/object#1360035307075000 ./dir |
- |
- will retrieve the second most recent version of the object. |
- |
- Note that version-specific URIs cannot be the target of the gsutil cp |
- command (trying to do so will result in an error), because writing to a |
- versioned object always creates a new version. |
- |
- If an object has been deleted, it will not show up in a normal gsutil ls |
- listing (i.e., ls without the -a option). You can restore a deleted object by |
- running gsutil ls -a to find the available versions, and then copying one of |
- the version-specific URIs to the version-less URI, for example: |
- |
- gsutil cp gs://bucket/object#1360101007329000 gs://bucket/object |
- |
- Note that when you do this it creates a new object version, which will incur |
- additional charges. You can get rid of the extra copy by deleting the older |
- version-specfic object: |
- |
- gsutil rm gs://bucket/object#1360101007329000 |
- |
- Or you can combine the two steps by using the gsutil mv command: |
- |
- gsutil mv gs://bucket/object#1360101007329000 gs://bucket/object |
- |
- If you want to remove all versions of an object use the gsutil rm -a option: |
- |
- gsutil rm -a gs://bucket/object |
- |
- Note that there is no limit to the number of older versions of an object you |
- will create if you continue to upload to the same object in a versioning- |
- enabled bucket. It is your responsibility to delete versions beyond the ones |
- you want to retain. |
- |
- |
-<B>COPYING VERSIONED BUCKETS</B> |
- You can copy data between two versioned buckets, using a command like: |
- |
- gsutil cp -r gs://bucket1/* gs://bucket2 |
- |
- When run using versioned buckets, this command will cause every object version |
- to be copied. The copies made in gs://bucket2 will have different generation |
- numbers (since a new generation is assigned when the object copy is made), |
- but the object sort order will remain consistent. For example, gs://bucket1 |
- might contain: |
- |
- % gsutil ls -la gs://bucket1 10 2013-06-06T02:33:11Z |
- 53 2013-02-02T22:30:57Z gs://bucket1/file#1359844257574000 metageneration=1 |
- 12 2013-02-02T22:30:57Z gs://bucket1/file#1359844257615000 metageneration=1 |
- 97 2013-02-02T22:30:57Z gs://bucket1/file#1359844257665000 metageneration=1 |
- |
- and after the copy, gs://bucket2 might contain: |
- |
- % gsutil ls -la gs://bucket2 |
- 53 2013-06-06T02:33:11Z gs://bucket2/file#1370485991580000 metageneration=1 |
- 12 2013-06-06T02:33:14Z gs://bucket2/file#1370485994328000 metageneration=1 |
- 97 2013-06-06T02:33:17Z gs://bucket2/file#1370485997376000 metageneration=1 |
- |
- Note that the object versions are in the same order (as can be seen by the |
- same sequence of sizes in both listings), but the generation numbers (and |
- timestamps) are newer in gs://bucket2. |
- |
- WARNING: If you use the gsutil -m option when copying the objects (to parallel |
- copy the data), object version ordering will NOT be preserved. All object |
- versions will be copied, but (for example) the latest/live version in the |
- destination bucket might be from one of the earlier versions in the source |
- bucket (and similarly, other versions may be out of order). When copying |
- versioned data it is advisable not to use the gsutil -m option. |
- |
- |
-<B>CONCURRENCY CONTROL</B> |
- If you are building an application using Google Cloud Storage, you may need to |
- be careful about concurrency control. Normally gsutil itself isn't used for |
- this purpose, but it's possible to write scripts around gsutil that perform |
- concurrency control. |
- |
- For example, suppose you want to implement a "rolling update" system using |
- gsutil, where a periodic job computes some data and uploads it to the cloud. |
- On each run, the job starts with the data that it computed from last run, and |
- computes a new value. To make this system robust, you need to have multiple |
- machines on which the job can run, which raises the possibility that two |
- simultaneous runs could attempt to update an object at the same time. This |
- leads to the following potential race condition: |
- |
- - job 1 computes the new value to be written |
- - job 2 computes the new value to be written |
- - job 2 writes the new value |
- - job 1 writes the new value |
- |
- In this case, the value that job 1 read is no longer current by the time |
- it goes to write the updated object, and writing at this point would result |
- in stale (or, depending on the application, corrupt) data. |
- |
- To prevent this, you can find the version-specific name of the object that was |
- created, and then use the information contained in that URI to specify an |
- x-goog-if-generation-match header on a subsequent gsutil cp command. You can |
- do this in two steps. First, use the gsutil cp -v option at upload time to get |
- the version-specific name of the object that was created, for example: |
- |
- gsutil cp -v file gs://bucket/object |
- |
- might output: |
- |
- Created: gs://bucket/object#1360432179236000 |
- |
- You can extract the generation value from this object and then construct a |
- subsequent gsutil command like this: |
- |
- gsutil -h x-goog-if-generation-match:1360432179236000 cp newfile \\ |
- gs://bucket/object |
- |
- This command requests Google Cloud Storage to attempt to upload newfile |
- but to fail the request if the generation of newfile that is live at the |
- time of the upload does not match that specified. |
- |
- If the command you use updates object metadata, you will need to find the |
- current metageneration for an object. To do this, use the gsutil ls -a and |
- -l options. For example, the command: |
- |
- gsutil ls -l -a gs://bucket/object |
- |
- will output something like: |
- |
- 64 2013-02-12T19:59:13Z gs://bucket/object#1360699153986000 metageneration=3 |
- 1521 2013-02-13T02:04:08Z gs://bucket/object#1360721048778000 metageneration=2 |
- |
- Given this information, you could use the following command to request setting |
- the ACL on the older version of the object, such that the command will fail |
- unless that is the current version of the data+metadata: |
- |
- gsutil -h x-goog-if-generation-match:1360699153986000 -h \\ |
- x-goog-if-metageneration-match:3 acl set public-read \\ |
- gs://bucket/object#1360699153986000 |
- |
- Without adding these headers, the update would simply overwrite the existing |
- ACL. Note that in contrast, the "gsutil acl ch" command uses these headers |
- automatically, because it performs a read-modify-write cycle in order to edit |
- ACLs. |
- |
- If you want to experiment with how generations and metagenerations work, try |
- the following. First, upload an object; then use gsutil ls -l -a to list all |
- versions of the object, along with each version's metageneration; then re- |
- upload the object and repeat the gsutil ls -l -a. You should see two object |
- versions, each with metageneration=1. Now try setting the ACL, and rerun the |
- gsutil ls -l -a. You should see the most recent object generation now has |
- metageneration=2. |
- |
- |
-<B>FOR MORE INFORMATION</B> |
- For more details on how to use versioning and preconditions, see |
- https://developers.google.com/storage/docs/object-versioning |
-""") |
- |
- |
-class CommandOptions(HelpProvider): |
- """Additional help about object versioning.""" |
- |
- # Help specification. See help_provider.py for documentation. |
- help_spec = HelpProvider.HelpSpec( |
- help_name='versions', |
- help_name_aliases=['concurrency', 'concurrency control'], |
- help_type='additional_help', |
- help_one_line_summary='Object Versioning and Concurrency Control', |
- help_text=_DETAILED_HELP_TEXT, |
- subcommand_help_text={}, |
- ) |