“`” \u5728MapReduce\u6574\u4e2a\u8fc7\u7a0b\u4e2d\uff0ccombiner\u662f\u53ef\u6709\u53ef\u65e0\u7684\uff0c\u9700\u8981\u662f\u81ea\u5df1\u7684\u60c5\u51b5\u800c\u5b9a\uff0c\u5982\u679c\u53ea\u662f\u5355\u7eaf\u7684\u5bf9map\u8f93\u51fa\u7684key-value\u8fdb\u884c\u4e00\u4e2a\u7edf\u8ba1\uff0c\u5219\u4e0d\u9700\u8981\u8fdb\u884ccombiner\uff0ccombiner\u76f8\u5f53\u4e8e\u63d0\u524d\u505a\u4e86\u4e00\u4e2areduce\u7684\u5de5\u4f5c\uff0c\u51cf\u8f7b\u4e86reduce\u7aef\u7684\u538b\u529b\uff0c<\/p>\n
Combiner\u53ea\u5e94\u8be5\u9002\u7528\u4e8e\u90a3\u79cdReduce\u7684\u8f93\u5165\uff08key\uff1avalue\u4e0e\u8f93\u51fa\uff08key\uff1avalue\uff09\u7c7b\u578b\u5b8c\u5168\u4e00\u81f4\uff0c\u4e14\u4e0d\u5f71\u54cd\u6700\u7ec8\u7ed3\u679c\u7684\u573a\u666f\u3002\u6bd4\u5982\u7d2f\u52a0\uff0c\u6700\u5927\u503c\u7b49\uff0c\u4e5f\u53ef\u4ee5\u7528\u4e8e\u8fc7\u6ee4\u6570\u636e\uff0c\u5728 map\u7aef\u5c06\u65e0\u6548\u7684\u6570\u636e\u8fc7\u6ee4\u6389\u3002<\/p>\n
\u5728\u8fd9\u4e9b\u9700\u6c42\u573a\u666f\u4e0b\uff0c\u8f93\u51fa\u7684\u6570\u636e\u662f\u53ef\u4ee5\u6839\u636ekey\u503c\u6765\u4f5c\u5408\u5e76\u7684\uff0c\u5408\u5e76\u7684\u76ee\u7684\u662f\u51cf\u5c11\u8f93\u51fa\u7684\u6570\u636e\u91cf\uff0c\u51cf\u5c11IO\u7684\u8bfb\u5199\uff0c\u51cf\u5c11\u7f51\u7edc\u4f20\u8f93,\u4ee5\u63d0\u9ad8MR\u7684\u4f5c\u4e1a\u6548\u7387\u3002<\/p>\n
1.combiner\u7684\u4f5c\u7528\u5c31\u662f\u5728map\u7aef\u5bf9\u8f93\u51fa\u5148\u505a\u4e00\u6b21\u5408\u5e76,\u4ee5\u51cf\u5c11\u4f20\u8f93\u5230reducer\u7684\u6570\u636e\u91cf.<\/p>\n
2.combiner\u6700\u57fa\u672c\u662f\u5b9e\u73b0\u672c\u5730key\u7684\u5f52\u5e76,\u5177\u6709\u7c7b\u4f3c\u672c\u5730reduce,\u90a3\u4e48\u6240\u6709\u7684\u7ed3\u679c\u90fd\u662freduce\u5b8c\u6210,\u6548\u7387\u4f1a\u76f8\u5bf9\u964d\u4f4e\u3002<\/p>\n
3.\u4f7f\u7528combiner,\u5148\u5b8c\u6210\u7684map\u4f1a\u5728\u672c\u5730\u805a\u5408,\u63d0\u5347\u901f\u5ea6.<\/p>\n
<pre><code>–partition\u610f\u601d\u4e3a\u5206\u5f00\uff0c\u5206\u533a\u3002\u5b83\u5206\u5272map\u6bcf\u4e2a\u8282\u70b9\u7684\u7ed3\u679c\uff0c\u6309\u7167key\u5206\u522b\u6620\u5c04\u7ed9\u4e0d\u540c\u7684reduce\uff0c\u4e5f\u662f\u53ef\u4ee5\u81ea\u5b9a\u4e49\u7684\u3002\u5176\u5b9e\u53ef\u4ee5\u7406\u89e3\u5f52\u7c7b\u3002\u4e5f\u53ef\u4ee5\u7406\u89e3\u4e3a\u6839\u636ekey\u6216value\u53careduce\u7684\u6570\u91cf\u6765\u51b3\u5b9a\u5f53\u524d\u7684\u8fd9\u5bf9\u8f93\u51fa\u6570\u636e\u6700\u7ec8\u5e94\u8be5\u4ea4\u7531\u54ea\u4e2areduce task\u5904\u7406
\n<\/code><\/pre><\/p>\n
partition\u7684\u4f5c\u7528\u5c31\u662f\u628a\u8fd9\u4e9b\u6570\u636e\u5f52\u7c7b\u3002\u6bcf\u4e2amap\u4efb\u52a1\u4f1a\u9488\u5bf9\u8f93\u51fa\u8fdb\u884c\u5206\u533a\uff0c\u53ca\u5bf9\u6bcf\u4e00\u4e2areduce\u4efb\u52a1\u5efa\u7acb\u4e00\u4e2a\u5206\u533a\u3002\u5212\u5206\u5206\u533a\u7531\u7528\u6237\u5b9a\u4e49\u7684partition\u51fd\u6570\u63a7\u5236\uff0c\u9ed8\u8ba4\u4f7f\u7528\u54c8\u5e0c\u51fd\u6570\u6765\u5212\u5206\u5206\u533a\u3002
\nHashPartitioner\u662fmapreduce\u7684\u9ed8\u8ba4partitioner\u3002\u8ba1\u7b97\u65b9\u6cd5\u662f <\/p>\n
which reducer=(key.hashCode() & Integer.MAX_VALUE) % numReduceTasks\uff0c\u5f97\u5230\u5f53\u524d\u7684\u76ee\u7684reducer\u3002<\/p>\n
<pre><code> "“`
\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
“`” \u5728MapReduce\u6574\u4e2a\u8fc7\u7a0b\u4e2d\uff0ccombiner\u662f\u53ef\u6709\u53ef\u65e0\u7684\uff0c\u9700\u8981\u662f\u81ea\u5df1\u7684\u60c5\u51b5 […]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-47549","post","type-post","status-publish","format-standard","hentry","category-c"],"_links":{"self":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/47549","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/users\/7"}],"replies":[{"embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/comments?post=47549"}],"version-history":[{"count":1,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/47549\/revisions"}],"predecessor-version":[{"id":47550,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/47549\/revisions\/47550"}],"wp:attachment":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/media?parent=47549"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/categories?post=47549"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/tags?post=47549"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}