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226 | <h1>Archives Guide</h1> |
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227 | <div id="minitoc-area"> |
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228 | <ul class="minitoc"> |
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229 | <li> |
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230 | <a href="#What+are+Hadoop+archives%3F"> What are Hadoop archives? </a> |
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231 | </li> |
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232 | <li> |
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233 | <a href="#How+to+create+an+archive%3F"> How to create an archive? </a> |
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234 | </li> |
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235 | <li> |
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236 | <a href="#How+to+look+up+files+in+archives%3F"> How to look up files in archives? </a> |
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239 | </div> |
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240 | |
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241 | <a name="N1000D"></a><a name="What+are+Hadoop+archives%3F"></a> |
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242 | <h2 class="h3"> What are Hadoop archives? </h2> |
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243 | <div class="section"> |
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244 | <p> |
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245 | Hadoop archives are special format archives. A Hadoop archive |
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246 | maps to a file system directory. A Hadoop archive always has a *.har |
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247 | extension. A Hadoop archive directory contains metadata (in the form |
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248 | of _index and _masterindex) and data (part-*) files. The _index file contains |
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249 | the name of the files that are part of the archive and the location |
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250 | within the part files. |
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251 | </p> |
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252 | </div> |
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253 | |
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254 | <a name="N10017"></a><a name="How+to+create+an+archive%3F"></a> |
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255 | <h2 class="h3"> How to create an archive? </h2> |
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256 | <div class="section"> |
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257 | <p> |
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258 | |
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259 | <span class="codefrag">Usage: hadoop archive -archiveName name <src>* <dest></span> |
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260 | |
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261 | </p> |
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262 | <p> |
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263 | -archiveName is the name of the archive you would like to create. |
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264 | An example would be foo.har. The name should have a *.har extension. |
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265 | The inputs are file system pathnames which work as usual with regular |
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266 | expressions. The destination directory would contain the archive. |
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267 | Note that this is a Map/Reduce job that creates the archives. You would |
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268 | need a map reduce cluster to run this. The following is an example:</p> |
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269 | <p> |
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270 | |
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271 | <span class="codefrag">hadoop archive -archiveName foo.har /user/hadoop/dir1 /user/hadoop/dir2 /user/zoo/</span> |
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272 | |
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273 | </p> |
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274 | <p> |
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275 | In the above example /user/hadoop/dir1 and /user/hadoop/dir2 will be |
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276 | archived in the following file system directory -- /user/zoo/foo.har. |
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277 | The sources are not changed or removed when an archive is created. |
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278 | </p> |
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279 | </div> |
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280 | |
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281 | <a name="N1002F"></a><a name="How+to+look+up+files+in+archives%3F"></a> |
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282 | <h2 class="h3"> How to look up files in archives? </h2> |
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283 | <div class="section"> |
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284 | <p> |
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285 | The archive exposes itself as a file system layer. So all the fs shell |
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286 | commands in the archives work but with a different URI. Also, note that |
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287 | archives are immutable. So, rename's, deletes and creates return |
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288 | an error. URI for Hadoop Archives is |
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289 | </p> |
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290 | <p> |
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291 | <span class="codefrag">har://scheme-hostname:port/archivepath/fileinarchive</span> |
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292 | </p> |
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293 | <p> |
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294 | If no scheme is provided it assumes the underlying filesystem. |
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295 | In that case the URI would look like |
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296 | </p> |
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297 | <p> |
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298 | <span class="codefrag"> |
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299 | har:///archivepath/fileinarchive</span> |
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300 | </p> |
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301 | <p> |
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302 | Here is an example of archive. The input to the archives is /dir. The directory dir contains |
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303 | files filea, fileb. To archive /dir to /user/hadoop/foo.har, the command is |
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304 | </p> |
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305 | <p> |
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306 | <span class="codefrag">hadoop archive -archiveName foo.har /dir /user/hadoop</span> |
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307 | |
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308 | </p> |
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309 | <p> |
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310 | To get file listing for files in the created archive |
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311 | </p> |
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312 | <p> |
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313 | <span class="codefrag">hadoop dfs -lsr har:///user/hadoop/foo.har</span> |
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314 | </p> |
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315 | <p>To cat filea in archive - |
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316 | </p> |
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317 | <p> |
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318 | <span class="codefrag">hadoop dfs -cat har:///user/hadoop/foo.har/dir/filea</span> |
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319 | </p> |
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