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| 1 # -*- coding: utf-8 -*- | |
| 2 # Copyright 2012 Google Inc. All Rights Reserved. | |
| 3 # | |
| 4 # Licensed under the Apache License, Version 2.0 (the "License"); | |
| 5 # you may not use this file except in compliance with the License. | |
| 6 # You may obtain a copy of the License at | |
| 7 # | |
| 8 # http://www.apache.org/licenses/LICENSE-2.0 | |
| 9 # | |
| 10 # Unless required by applicable law or agreed to in writing, software | |
| 11 # distributed under the License is distributed on an "AS IS" BASIS, | |
| 12 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | |
| 13 # See the License for the specific language governing permissions and | |
| 14 # limitations under the License. | |
| 15 """Additional help about using gsutil for production tasks.""" | |
| 16 | |
| 17 from __future__ import absolute_import | |
| 18 | |
| 19 from gslib.help_provider import HelpProvider | |
| 20 | |
| 21 _DETAILED_HELP_TEXT = (""" | |
| 22 <B>OVERVIEW</B> | |
| 23 If you use gsutil in large production tasks (such as uploading or | |
| 24 downloading many GiBs of data each night), there are a number of things | |
| 25 you can do to help ensure success. Specifically, this section discusses | |
| 26 how to script large production tasks around gsutil's resumable transfer | |
| 27 mechanism. | |
| 28 | |
| 29 | |
| 30 <B>BACKGROUND ON RESUMABLE TRANSFERS</B> | |
| 31 First, it's helpful to understand gsutil's resumable transfer mechanism, | |
| 32 and how your script needs to be implemented around this mechanism to work | |
| 33 reliably. gsutil uses resumable transfer support when you attempt to upload | |
| 34 or download a file larger than a configurable threshold (by default, this | |
| 35 threshold is 2 MiB). When a transfer fails partway through (e.g., because of | |
| 36 an intermittent network problem), gsutil uses a truncated randomized binary | |
| 37 exponential backoff-and-retry strategy that by default will retry transfers up | |
| 38 to 6 times over a 63 second period of time (see "gsutil help retries" for | |
| 39 details). If the transfer fails each of these attempts with no intervening | |
| 40 progress, gsutil gives up on the transfer, but keeps a "tracker" file for | |
| 41 it in a configurable location (the default location is ~/.gsutil/, in a file | |
| 42 named by a combination of the SHA1 hash of the name of the bucket and object | |
| 43 being transferred and the last 16 characters of the file name). When transfers | |
| 44 fail in this fashion, you can rerun gsutil at some later time (e.g., after | |
| 45 the networking problem has been resolved), and the resumable transfer picks | |
| 46 up where it left off. | |
| 47 | |
| 48 | |
| 49 <B>SCRIPTING DATA TRANSFER TASKS</B> | |
| 50 To script large production data transfer tasks around this mechanism, | |
| 51 you can implement a script that runs periodically, determines which file | |
| 52 transfers have not yet succeeded, and runs gsutil to copy them. Below, | |
| 53 we offer a number of suggestions about how this type of scripting should | |
| 54 be implemented: | |
| 55 | |
| 56 1. When resumable transfers fail without any progress 6 times in a row | |
| 57 over the course of up to 63 seconds, it probably won't work to simply | |
| 58 retry the transfer immediately. A more successful strategy would be to | |
| 59 have a cron job that runs every 30 minutes, determines which transfers | |
| 60 need to be run, and runs them. If the network experiences intermittent | |
| 61 problems, the script picks up where it left off and will eventually | |
| 62 succeed (once the network problem has been resolved). | |
| 63 | |
| 64 2. If your business depends on timely data transfer, you should consider | |
| 65 implementing some network monitoring. For example, you can implement | |
| 66 a task that attempts a small download every few minutes and raises an | |
| 67 alert if the attempt fails for several attempts in a row (or more or less | |
| 68 frequently depending on your requirements), so that your IT staff can | |
| 69 investigate problems promptly. As usual with monitoring implementations, | |
| 70 you should experiment with the alerting thresholds, to avoid false | |
| 71 positive alerts that cause your staff to begin ignoring the alerts. | |
| 72 | |
| 73 3. There are a variety of ways you can determine what files remain to be | |
| 74 transferred. We recommend that you avoid attempting to get a complete | |
| 75 listing of a bucket containing many objects (e.g., tens of thousands | |
| 76 or more). One strategy is to structure your object names in a way that | |
| 77 represents your transfer process, and use gsutil prefix wildcards to | |
| 78 request partial bucket listings. For example, if your periodic process | |
| 79 involves downloading the current day's objects, you could name objects | |
| 80 using a year-month-day-object-ID format and then find today's objects by | |
| 81 using a command like gsutil ls "gs://bucket/2011-09-27-*". Note that it | |
| 82 is more efficient to have a non-wildcard prefix like this than to use | |
| 83 something like gsutil ls "gs://bucket/*-2011-09-27". The latter command | |
| 84 actually requests a complete bucket listing and then filters in gsutil, | |
| 85 while the former asks Google Storage to return the subset of objects | |
| 86 whose names start with everything up to the "*". | |
| 87 | |
| 88 For data uploads, another technique would be to move local files from a "to | |
| 89 be processed" area to a "done" area as your script successfully copies | |
| 90 files to the cloud. You can do this in parallel batches by using a command | |
| 91 like: | |
| 92 | |
| 93 gsutil -m cp -r to_upload/subdir_$i gs://bucket/subdir_$i | |
| 94 | |
| 95 where i is a shell loop variable. Make sure to check the shell $status | |
| 96 variable is 0 after each gsutil cp command, to detect if some of the copies | |
| 97 failed, and rerun the affected copies. | |
| 98 | |
| 99 With this strategy, the file system keeps track of all remaining work to | |
| 100 be done. | |
| 101 | |
| 102 4. If you have really large numbers of objects in a single bucket | |
| 103 (say hundreds of thousands or more), you should consider tracking your | |
| 104 objects in a database instead of using bucket listings to enumerate | |
| 105 the objects. For example this database could track the state of your | |
| 106 downloads, so you can determine what objects need to be downloaded by | |
| 107 your periodic download script by querying the database locally instead | |
| 108 of performing a bucket listing. | |
| 109 | |
| 110 5. Make sure you don't delete partially downloaded files after a transfer | |
| 111 fails: gsutil picks up where it left off (and performs an MD5 check of | |
| 112 the final downloaded content to ensure data integrity), so deleting | |
| 113 partially transferred files will cause you to lose progress and make | |
| 114 more wasteful use of your network. You should also make sure whatever | |
| 115 process is waiting to consume the downloaded data doesn't get pointed | |
| 116 at the partially downloaded files. One way to do this is to download | |
| 117 into a staging directory and then move successfully downloaded files to | |
| 118 a directory where consumer processes will read them. | |
| 119 | |
| 120 6. If you have a fast network connection, you can speed up the transfer of | |
| 121 large numbers of files by using the gsutil -m (multi-threading / | |
| 122 multi-processing) option. Be aware, however, that gsutil doesn't attempt to | |
| 123 keep track of which files were downloaded successfully in cases where some | |
| 124 files failed to download. For example, if you use multi-threaded transfers | |
| 125 to download 100 files and 3 failed to download, it is up to your scripting | |
| 126 process to determine which transfers didn't succeed, and retry them. A | |
| 127 periodic check-and-run approach like outlined earlier would handle this | |
| 128 case. | |
| 129 | |
| 130 If you use parallel transfers (gsutil -m) you might want to experiment with | |
| 131 the number of threads being used (via the parallel_thread_count setting | |
| 132 in the .boto config file). By default, gsutil uses 10 threads for Linux | |
| 133 and 24 threads for other operating systems. Depending on your network | |
| 134 speed, available memory, CPU load, and other conditions, this may or may | |
| 135 not be optimal. Try experimenting with higher or lower numbers of threads | |
| 136 to find the best number of threads for your environment. | |
| 137 | |
| 138 <B>RUNNING GSUTIL ON MULTIPLE MACHINES</B> | |
| 139 When running gsutil on multiple machines that are all attempting to use the | |
| 140 same OAuth2 refresh token, it is possible to encounter rate limiting errors | |
| 141 for the refresh requests (especially if all of these machines are likely to | |
| 142 start running gsutil at the same time). To account for this, gsutil will | |
| 143 automatically retry OAuth2 refresh requests with a truncated randomized | |
| 144 exponential backoff strategy like that which is described in the | |
| 145 "BACKGROUND ON RESUMABLE TRANSFERS" section above. The number of retries | |
| 146 attempted for OAuth2 refresh requests can be controlled via the | |
| 147 "oauth2_refresh_retries" variable in the .boto config file. | |
| 148 """) | |
| 149 | |
| 150 | |
| 151 class CommandOptions(HelpProvider): | |
| 152 """Additional help about using gsutil for production tasks.""" | |
| 153 | |
| 154 # Help specification. See help_provider.py for documentation. | |
| 155 help_spec = HelpProvider.HelpSpec( | |
| 156 help_name='prod', | |
| 157 help_name_aliases=[ | |
| 158 'production', 'resumable', 'resumable upload', 'resumable transfer', | |
| 159 'resumable download', 'scripts', 'scripting'], | |
| 160 help_type='additional_help', | |
| 161 help_one_line_summary='Scripting Production Transfers', | |
| 162 help_text=_DETAILED_HELP_TEXT, | |
| 163 subcommand_help_text={}, | |
| 164 ) | |
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