\u5728\u4ee5\u5355\u8c03\u9012\u589e\u4e3b\u952e\u4e3a\u4e3b\u7684\u5199\u5165\u573a\u666f\u4e2d，\u7406\u8bba\u4e0a\u65b0\u751f\u6210\u7684 SSTable \u4e0e\u6df1\u5c42\u6570\u636e\u5c11\u6709\u952e\u91cd\u53e0，\u540e\u53f0\u5f52\u5e76\u7406\u5e94\u4ee5\u6781\u4f4e\u7684\u4ee3\u4ef7\u63a8\u8fdb\u3002\u7136\u800c\u5728\u7ebf\u4e0a\u7ef4\u62a4 RocksDB \u65f6，\u7ecf\u5e38\u80fd\u770b\u5230\u78c1\u76d8 I\/O \u6301\u7eed\u8dd1\u6ee1\u3001\u5199\u653e\u5927\u5c45\u9ad8\u4e0d\u4e0b\u7684\u60c5\u51b5\u2014\u2014\u5373\u4fbf\u4e1a\u52a1\u5199\u5165\u5728\u903b\u8f91\u4e0a\u5b8c\u5168\u6709\u5e8f，\u843d\u5230\u5b58\u50a8\u5f15\u64ce\u5e95\u5c42，\u6bcf\u4e00\u6b21\u8de8\u5c42\u538b\u5b9e\u4f9d\u7136\u5728\u9891\u7e41\u89e6\u53d1\u5168\u91cf\u7269\u7406\u91cd\u5199\u3002<\/p>\n
\u5f88\u591a\u5de5\u7a0b\u5e08\u5728\u6392\u67e5\u8fd9\u7c7b\u5199\u653e\u5927\u95ee\u9898\u65f6，\u901a\u5e38\u4f1a\u5173\u6ce8\u201c\u96f6\u62f7\u8d1d\u642c\u79fb\u201d（Trivial Move）\u3002\u76f4\u89c9\u4e0a，\u5982\u679c\u67d0\u4e2a\u5f85\u5f52\u5e76\u7684\u6587\u4ef6\u5728\u76ee\u6807\u5c42\u6ca1\u6709\u91cd\u53e0\u8303\u56f4，\u53ea\u9700\u5728\u5143\u6570\u636e\u6e05\u5355\u4e2d\u4fee\u6539\u6307\u9488\u5c06\u5176\u6c89\u5165\u4e0b\u5c42，\u4fbf\u80fd\u7701\u53bb\u6574\u76d8\u7269\u7406\u8bfb\u5199，\u8be5\u6b65\u5199\u653e\u5927\u4e5f\u76f4\u63a5\u5f52\u96f6\u3002\u4f46\u73b0\u5b9e\u5f80\u5f80\u4e0d\u5982\u4eba\u610f：\u4e0d\u4ec5\u96f6\u62f7\u8d1d\u642c\u79fb\u7684\u89e6\u53d1\u6982\u7387\u8fdc\u4f4e\u4e8e\u9884\u671f，\u751a\u81f3\u5728\u5c1d\u8bd5\u8c03\u6574\u5f52\u5e76\u5019\u9009\u4f18\u5148\u7ea7（compaction_pri）\u8bd5\u56fe\u6362\u53d6\u66f4\u4f4e\u5199\u653e\u5927\u65f6，\u53c8\u5e38\u4f1a\u610f\u5916\u5f15\u53d1\u201c\u5893\u7891\u957f\u671f\u65e0\u6cd5\u56de\u6536\u3001\u8bfb\u6027\u80fd\u5d29\u584c\u201d\u7684\u6b21\u751f\u95ee\u9898\u3002<\/p>\n
\u96f6\u62f7\u8d1d\u642c\u79fb\u7edd\u975e\u5355\u7eaf\u7684\u201c\u65e0\u91cd\u53e0\u5373\u653e\u884c\u201d，\u800c\u662f\u4e00\u5957\u53d7\u5230\u5c42\u7ea7\u62d3\u6251\u3001\u7956\u7236\u5c42\u91cd\u53e0\u3001\u5b58\u50a8\u4ecb\u8d28\u8def\u5f84\u4e0e\u538b\u7f29\u7b97\u6cd5\u4e25\u5bc6\u7ea6\u675f\u7684\u9632\u5fa1\u6027\u673a\u5236；\u540c\u5c42\u5019\u9009\u6587\u4ef6\u7684\u9009\u53d6，\u66f4\u662f\u5728\u5199\u653e\u5927\u3001\u7a7a\u95f4\u56de\u6536\u65f6\u6548\u4e0e\u5e76\u53d1\u541e\u5410\u4e4b\u95f4\u7684\u5de5\u7a0b\u6743\u8861\u3002\u672c\u6587\u7ed3\u5408 RocksDB \u5185\u6838\u6e90\u7801\u4e0e\u5b9e\u9645\u8c03\u4f18\u7ecf\u9a8c，\u7cfb\u7edf\u68b3\u7406\u00a0IsTrivialMove\u00a0\u7684\u5224\u5b9a\u6811\u3001\u6279\u91cf\u6269\u5c55\u673a\u5236，\u4ee5\u53ca\u4e94\u79cd\u00a0compaction_pri\u00a0\u7b56\u7565\u7684\u8bbe\u8ba1\u52a8\u673a\u4e0e\u7ebf\u4e0a\u9690\u60a3\u3002<\/p>\n
\u8981\u5398\u6e05\u96f6\u62f7\u8d1d\u642c\u79fb\u7684\u4ef7\u503c，\u9700\u5148\u5ba1\u89c6 Leveled Compaction \u6a21\u578b\u4e0b\u7684 I\/O \u653e\u5927\u903b\u8f91\u3002RocksDB \u5b98\u65b9\u5c06\u5199\u653e\u5927（Write Amplification, WA）\u5b9a\u4e49\u4e3a：<\/p>\n
$$\\\\text{WA} = \\\\frac{\\\\text{\u78c1\u76d8\u5b9e\u9645\u5199\u5165\u7269\u7406\u5b57\u8282\u6570}}{\\\\text{\u7528\u6237\u524d\u53f0\u5199\u5165\u4e1a\u52a1\u5b57\u8282\u6570}}$$<\/p>\n
\u4e3a\u4fdd\u969c\u9ad8\u541e\u5410\u7684\u5199\u5165\u80fd\u529b，\u5199\u5165\u8bf7\u6c42\u901a\u5e38\u5148\u8ffd\u52a0\u81f3\u9884\u5199\u65e5\u5fd7（WAL），\u5e76\u5728\u5185\u5b58\u4e2d\u7684 MemTable \u7ef4\u62a4\u8df3\u8868\u7ed3\u6784\u3002\u5f53 MemTable \u5199\u6ee1\u540e\u51bb\u7ed3\u5e76\u901a\u8fc7\u540e\u53f0 Flush \u7ebf\u7a0b\u987a\u5e8f\u843d\u76d8\u4e3a Level 0（L0）\u7684 SSTable \u6587\u4ef6\u3002\u7531\u4e8e\u5404 L0 \u6587\u4ef6\u7684\u952e\u8303\u56f4\u5b8c\u5168\u53d6\u51b3\u4e8e MemTable \u51bb\u7ed3\u65f6\u7684\u5185\u5b58\u72b6\u6001，\u56e0\u6b64 L0 \u6587\u4ef6\u95f4\u7684\u952e\u8303\u56f4\u5929\u7136\u5b58\u5728\u5927\u91cf\u91cd\u53e0\u3002\u4e3a\u4e86\u56de\u6536\u5386\u53f2\u591a\u7248\u672c\u3001\u6e05\u7406 Delete \u4ea7\u751f\u7684\u5893\u7891（Tombstone），\u5e76\u786e\u4fdd\u4ece L1 \u5f00\u59cb\u5404\u5c42\u5185\u90e8\u952e\u8303\u56f4\u4e25\u683c\u5168\u5c40\u9012\u589e\u4e14\u4e92\u4e0d\u91cd\u53e0，\u540e\u53f0 Compaction \u5fc5\u987b\u6301\u7eed\u8fd0\u884c\u3002<\/p>\n
\u5728\u7ecf\u5178 Leveled Compaction \u4e2d，L1 \u53ca\u4ee5\u4e0a\u5404\u5c42\u7684\u5bb9\u91cf\u901a\u5e38\u5448\u51e0\u4f55\u7ea7\u6570\u653e\u5927（\u9ed8\u8ba4\u653e\u5927\u56e0\u5b50\u4e3a 10）\u3002\u5047\u8bbe L1 \u5bb9\u91cf\u4e0a\u9650\u4e3a 10 MB，\u5219 L2 \u4e3a 100 MB，L3 \u4e3a 1 GB，\u4f9d\u6b64\u7c7b\u63a8\u3002\u5f53\u67d0\u5c42\u603b\u5bb9\u91cf\u8d85\u6807\u65f6，\u8c03\u5ea6\u5668\u4f1a\u4ece\u8be5\u5c42\u9009\u51fa\u5019\u9009\u6587\u4ef6，\u5e76\u5728\u76ee\u6807\u5c42\u627e\u51fa\u6240\u6709\u952e\u8303\u56f4\u76f8\u4ea4\u7684\u6587\u4ef6，\u5171\u540c\u62c9\u5165\u5185\u5b58\u6267\u884c\u591a\u8def\u5f52\u5e76\u6392\u5e8f，\u91cd\u65b0\u5207\u5206\u4e3a\u65b0\u7684 SSTable \u5199\u56de\u76ee\u6807\u5c42\u3002<\/p>\n
\u8fd9\u4e00\u8fc7\u7a0b\u7684\u7269\u7406 I\/O \u8d26\u672c\u6781\u4e3a\u654f\u611f：\u82e5\u5728 L1 \u9009\u4e2d\u4e00\u4e2a 10 MB \u7684\u6587\u4ef6，\u800c\u5b83\u5728 L2 \u4e2d\u4e0e 10 \u4e2a\u6587\u4ef6\u76f8\u4ea4（\u5bf9\u5e94\u7ea6 100 MB \u6570\u636e），\u4e3a\u4e86\u5c06\u8fd9 10 MB \u6570\u636e\u63a8\u8fdb\u5230 L2，\u540e\u53f0\u9700\u8981\u4ece\u78c1\u76d8\u8bfb\u53d6 110 MB \u6570\u636e，\u7ecf\u8fc7 CPU \u6bd4\u8f83\u89e3\u538b\u8fc7\u6ee4\u540e，\u518d\u5411\u78c1\u76d8\u5199\u5165 110 MB \u7684\u65b0\u6587\u4ef6\u3002\u4ec5\u8fd9\u4e00\u6b65\u8de8\u5c42\u5f52\u5e76，\u5c40\u90e8\u5199\u653e\u5927\u5c31\u8fbe\u5230\u4e86 11 \u500d\u3002\u6570\u636e\u4ece L0 \u6700\u7ec8\u4e0b\u6c89\u5230 L6 \u7684\u5168\u94fe\u8def\u7d2f\u79ef\u5199\u653e\u5927，\u5728\u7ebf\u4e0a\u5f80\u5f80\u9ad8\u8fbe 20 \u81f3 40 \u500d\u3002<\/p>\n
\u9ad8\u5199\u653e\u5927\u4e0d\u4ec5\u4f1a\u5927\u5e45\u52a0\u901f\u95ea\u5b58\u4ecb\u8d28\u7684\u78e8\u635f，\u66f4\u4f1a\u56e0\u4e89\u62a2\u78c1\u76d8\u5e26\u5bbd\u4e0e CPU \u5468\u671f，\u5bfc\u81f4\u524d\u53f0\u8bfb\u5199\u8bf7\u6c42\u51fa\u73b0\u4e25\u91cd\u7684\u6bdb\u523a\u548c\u6392\u961f\u8d85\u65f6\u3002\u82e5\u524d\u53f0\u5199\u5165\u901f\u7387\u6301\u7eed\u538b\u5236\u540e\u53f0\u5f52\u5e76\u901f\u7387，L0 \u6587\u4ef6\u5806\u79ef\u8fd8\u4f1a\u8fdb\u4e00\u6b65\u89e6\u53d1 Write Stall，\u8feb\u4f7f\u5ba2\u6237\u7aef\u8bf7\u6c42\u88ab\u9650\u6d41\u751a\u81f3\u963b\u585e\u6302\u8d77\u3002<\/p>\n
\u5728\u7269\u7406 I\/O \u6781\u5176\u654f\u611f\u7684\u573a\u666f\u4e0b，\u540e\u53f0\u5f52\u5e76\u627f\u62c5\u7740\u4e24\u4e2a\u4e92\u76f8\u5236\u8861\u7684\u804c\u8d23：<\/p>\n
\u5fc5\u987b\u7269\u7406\u91cd\u5199\u7684\u573a\u666f：\u6ca1\u6709\u89e3\u538b\u3001\u591a\u8def\u5f52\u5e76\u3001\u7248\u672c\u6bd4\u5bf9\u4e0e\u91cd\u5199，\u65e7\u7248\u672c\u6570\u636e\u4fbf\u65e0\u6cd5\u56de\u6536，Delete \u5893\u7891\u4fbf\u65e0\u6cd5\u6e05\u9664，\u540e\u7eed\u70b9\u67e5\u4e0e\u8303\u56f4\u626b\u63cf\u5fc5\u987b\u7a7f\u900f\u66f4\u591a\u65e0\u6548\u6570\u636e，\u5f15\u53d1\u8bfb\u653e\u5927\u4e0e\u7a7a\u95f4\u653e\u5927\u53cc\u91cd\u5931\u63a7\u3002<\/p>\n<\/li>\n
\u7eaf\u5c5e\u673a\u68b0\u91cd\u5199\u7684\u573a\u666f：\u82e5\u67d0\u4e9b\u6570\u636e\u672c\u8eab\u4e0d\u5b58\u5728\u591a\u7248\u672c\u5197\u4f59，\u4e14\u5728\u4e0b\u4e00\u5c42\u5e76\u65e0\u76f8\u4ea4\u6570\u636e，\u4f8b\u5982：<\/p>\n
\u4e1a\u52a1\u4e3b\u952e\u4e3a\u5355\u8c03\u9012\u589e\u7684\u65f6\u95f4\u6233\u6216\u81ea\u589e ID，\u65b0\u751f\u6210\u7684\u6570\u636e\u59cb\u7ec8\u843d\u5728\u5168\u5e93\u952e\u7a7a\u95f4\u7684\u7269\u7406\u8fb9\u7f18；<\/p>\n<\/li>\n
\u67d0\u4e2a\u5c42\u7ea7\u7684\u7279\u5b9a\u952e\u533a\u95f4\u8f83\u4e3a\u7a00\u758f，\u76ee\u6807\u5c42\u5bf9\u5e94\u7684\u952e\u8303\u56f4\u5b8c\u5168\u5904\u4e8e\u771f\u7a7a\u72b6\u6001；<\/p>\n<\/li>\n
\u79bb\u7ebf\u5bfc\u5165\u7684\u5df2\u5168\u5c40\u6392\u5e8f\u6570\u636e\u96c6，\u5404\u5c42\u95f4\u5929\u7136\u8fb9\u754c\u6b63\u4ea4\u3002<\/p>\n<\/li>\n<\/ul>\n<\/li>\n
\u6b64\u65f6\u82e5\u4f9d\u7136\u542f\u52a8\u591a\u8def\u5f52\u5e76\u8fed\u4ee3\u5668，\u5bf9\u6570\u636e\u5757\u9010\u4e00\u89e3\u538b\u3001\u590d\u5236\u3001\u91cd\u65b0\u8ba1\u7b97 Checksum\u3001\u91cd\u5efa\u5e03\u9686\u8fc7\u6ee4\u5668\u5e76\u91cd\u65b0\u5199\u76d8，\u5b9e\u9645\u4e0a\u5e76\u672a\u6e05\u7406\u4efb\u4f55\u5783\u573e\u6570\u636e，\u4ec5\u4ec5\u662f\u5c06\u8be5 SSTable \u5728\u903b\u8f91\u5c42\u7ea7\u4e0a\u5411\u4e0b\u63a8\u8fdb\u4e86\u4e00\u5c42，\u5374\u5f92\u589e\u4e86\u6570\u5341\u81f3\u6570\u767e\u5146\u5b57\u8282\u7684\u78c1\u76d8 I\/O \u5f00\u9500\u3002<\/p>\n
\u96f6\u62f7\u8d1d\u642c\u79fb\u00a0IsTrivialMove\u00a0\u4fbf\u662f\u4e13\u95e8\u7528\u4e8e\u907f\u514d\u4e0a\u8ff0\u673a\u68b0\u91cd\u5199\u7684\u4f18\u5316\u8def\u5f84\u3002<\/p>\n
\u6240\u8c13\u96f6\u62f7\u8d1d，\u6307\u8be5\u6b21 Compaction \u4e0d\u5bf9\u78c1\u76d8\u4e0a\u7684\u5e95\u5c42 SSTable \u6587\u4ef6\u8fdb\u884c\u4efb\u4f55\u7269\u7406\u8bfb\u53d6\u3001\u89e3\u6790\u4e0e\u91cd\u65b0\u7f16\u7801\u3002\u5176\u5168\u90e8\u5f00\u9500，\u4ec5\u662f\u5728 MANIFEST \u6e05\u5355\u4e2d\u8ffd\u52a0\u4e00\u6761\u7248\u672c\u53d8\u66f4\u8bb0\u5f55（VersionEdit）：\u4ece\u6e90\u5c42\u6ce8\u9500\u8be5\u6587\u4ef6\u5143\u6570\u636e，\u5e76\u5728\u76ee\u6807\u5c42\u91cd\u65b0\u767b\u8bb0\u8be5\u6587\u4ef6，\u968f\u540e\u5728\u5185\u5b58\u4e2d\u53d1\u5e03\u65b0\u7684\u7248\u672c\u5feb\u7167\u3002<\/p>\n
\u5728 RocksDB \u6e90\u7801\u00a0db\/db_impl\/db_impl_compaction_flush.cc\u00a0\u4e2d，DBImpl::PrepareTrivialMoveEdit\u00a0\u5c55\u73b0\u4e86\u8fd9\u4e00\u8fc7\u7a0b\u7684\u5e95\u5c42\u5b9e\u73b0：<\/p>\n
C++<\/p>\n
void DBImpl::PrepareTrivialMoveEdit(Compaction& c, LogBuffer* log_buffer,
\n size_t& moved_files, size_t& moved_bytes) {
\n mutex_.AssertHeld();<\/p>\n
ROCKS_LOG_BUFFER(log_buffer, "[%s] Moving %d files to level-%d\\\\n",
\n c.column_family_data()->GetName().c_str(),
\n static_cast<int>(c.num_input_files(0)), c.output_level());<\/p>\n
\/\/ \u4ec5\u5411 VersionEdit \u5199\u5165\u5143\u6570\u636e\u53d8\u66f4，\u5b9e\u73b0\u6587\u4ef6\u8de8\u5c42\u79fb\u52a8
\n for (unsigned int l = 0; l < c.num_input_levels(); l++) {
\n if (c.level(l) == c.output_level()) {
\n continue;
\n }
\n for (size_t i = 0; i < c.num_input_files(l); i++) {
\n FileMetaData* f = c.input(l, i);
\n \/\/ 1. \u5728\u6e90\u5c42\u6807\u8bb0\u6ce8\u9500\u8be5\u6587\u4ef6
\n c.edit()->DeleteFile(c.level(l), f->fd.GetNumber());
\n \/\/ 2. \u5728\u76ee\u6807\u5c42\u4ee5\u539f\u6709\u7269\u7406\u5c5e\u6027\u91cd\u65b0\u767b\u8bb0\u8be5\u6587\u4ef6
\n c.edit()->AddFile(
\n c.output_level(), f->fd.GetNumber(), f->fd.GetPathId(),
\n f->fd.GetFileSize(), f->smallest, f->largest, f->fd.smallest_seqno,
\n f->fd.largest_seqno, f->marked_for_compaction, f->temperature,
\n f->oldest_blob_file_number, f->oldest_ancester_time,
\n f->file_creation_time, f->epoch_number, f->file_checksum,
\n f->file_checksum_func_name, f->unique_id,
\n f->compensated_range_deletion_size, f->tail_size,
\n f->user_defined_timestamps_persisted, f->min_timestamp,
\n f->max_timestamp, f->file_open_metadata);
\n moved_bytes += static_cast<size_t>(c.input(l, i)->fd.GetFileSize());
\n }
\n moved_files += c.num_input_files(l);
\n }
\n}<\/p>\n
\u5728\u6574\u4e2a\u51fd\u6570\u4e2d，\u6ca1\u6709\u4efb\u4f55\u6d89\u53ca\u5e95\u5c42\u6587\u4ef6\u7684 I\/O \u8bfb\u5199\u8c03\u7528\u3002\u6838\u5fc3\u64cd\u4f5c\u4ec5\u5305\u542b：<\/p>\n
c.edit()->DeleteFile(\u6e90\u5c42, \u6587\u4ef6\u53f7)；<\/p>\n<\/li>\n
c.edit()->AddFile(\u76ee\u6807\u5c42, \u6587\u4ef6\u53f7, …)\u3002<\/p>\n<\/li>\n
\u8fd9\u4e24\u4e2a\u64cd\u4f5c\u88ab\u6253\u5305\u5199\u5165 MANIFEST，\u5e76\u5728\u5185\u5b58\u4e2d\u66f4\u65b0\u7248\u672c\u6620\u5c04\u3002\u5bf9\u4e8e\u4e00\u4e2a 64 MB \u7684 SST \u6587\u4ef6，\u539f\u672c\u9700\u8981\u6570\u767e\u6beb\u79d2\u7684\u7269\u7406\u8bfb\u5199\u4e0e\u5927\u91cf I\/O \u8d44\u6e90，\u5728 Trivial Move \u8def\u5f84\u4e0b\u88ab\u7f29\u51cf\u4e3a\u51e0\u5341\u5fae\u79d2\u7ea7\u522b\u7684\u5355\u6b21\u5143\u6570\u636e\u65e5\u5fd7\u63d0\u4ea4\u3002<\/p>\n
\u8bb8\u591a\u5de5\u7a0b\u5e08\u5e38\u62b1\u6709\u4e00\u4e2a\u76f4\u89c9\u5047\u8bbe：\u53ea\u8981\u6e90\u5c42\u9009\u4e2d\u7684\u6587\u4ef6\u5728\u76ee\u6807\u5c42\u6ca1\u6709\u952e\u4ea4\u53e0，\u7cfb\u7edf\u5c31\u5fc5\u7136\u8d70\u96f6\u62f7\u8d1d\u901a\u9053\u3002<\/p>\n
\u8fd9\u4e00\u5fc3\u667a\u6a21\u578b\u5e76\u4e0d\u6210\u7acb，\u4e5f\u662f\u5bfc\u81f4\u5f88\u591a\u7ebf\u4e0a\u5b9e\u4f8b\u201c\u9884\u671f\u80fd\u96f6\u62f7\u8d1d\u5374\u9891\u906d\u5168\u91cf\u91cd\u5199\u201d\u7684\u6280\u672f\u7591\u60d1\u6839\u6e90\u3002\u5728 RocksDB \u5185\u90e8，\u5373\u4fbf\u76ee\u6807\u5c42\u5b8c\u5168\u6ca1\u6709\u76f8\u4ea4\u6570\u636e，\u8c03\u5ea6\u5668\u4ecd\u6709\u5927\u6982\u7387\u5426\u51b3\u96f6\u62f7\u8d1d，\u5f3a\u5236\u5c06\u5176\u9001\u5165\u5e38\u89c4\u91cd\u5199\u6d41\u7a0b\u3002\u5176\u80cc\u540e\u539f\u56e0\u901a\u5e38\u6db5\u76d6：<\/p>\n
\u5c06\u8be5\u6587\u4ef6\u4e0b\u6c89\u81f3\u76ee\u6807\u5c42\u540e，\u662f\u5426\u4f1a\u5bfc\u81f4\u5728\u672a\u6765\u4e0e\u7956\u7236\u5c42\u4ea7\u751f\u4e0d\u53ef\u63a7\u7684\u8d85\u5927\u91cd\u53e0？<\/p>\n<\/li>\n
\u5b9e\u4f8b\u662f\u5426\u914d\u7f6e\u4e86\u591a\u78c1\u76d8\u8def\u5f84（db_paths），\u5bfc\u81f4\u6e90\u6587\u4ef6\u7269\u7406\u5b58\u50a8\u5377\u4e0e\u76ee\u6807\u5c42\u8bbe\u5b9a\u5377\u4e0d\u4e00\u81f4？<\/p>\n<\/li>\n
\u5404\u5c42\u7ea7\u4e4b\u95f4\u662f\u5426\u914d\u7f6e\u4e86\u4e0d\u540c\u7684\u538b\u7f29\u7b97\u6cd5（CompressionType）？<\/p>\n<\/li>\n
\u662f\u5426\u6ce8\u518c\u4e86\u5fc5\u987b\u9010\u6761\u6267\u884c\u6821\u9a8c\u7684\u00a0CompactionFilter？<\/p>\n<\/li>\n
\u662f\u5426\u914d\u7f6e\u4e86\u6309\u524d\u7f00\u5207\u5272\u7684\u00a0SstPartitioner\u00a0\u5e76\u8de8\u8d8a\u4e86\u5206\u5272\u7ebf？<\/p>\n<\/li>\n<\/ul>\n
\u96f6\u62f7\u8d1d\u642c\u79fb\u5fc5\u987b\u6ee1\u8db3\u4e00\u7ec4\u4e92\u4e3a\u524d\u7f6e\u7684\u9632\u5fa1\u6027\u7ea6\u675f\u3002<\/p>\n
\u5206\u5c42\u5f52\u5e76\u7684\u4efb\u52a1\u7ec4\u88c5\u7531\u00a0LevelCompactionPicker\u00a0\u53ca\u5176\u5185\u90e8\u8f85\u52a9\u7c7b\u00a0LevelCompactionBuilder\u00a0\u4e3b\u5bfc（\u4ee3\u7801\u4f4d\u4e8e\u00a0db\/compaction\/compaction_picker_level.cc\u00a0\u4e2d\u7684\u00a0PickCompaction()）\u3002\u5176\u6838\u5fc3\u6d41\u7a0b\u5982\u4e0b：<\/p>\n
\u786e\u5b9a\u6e90\u5c42\u4e0e\u76ee\u6807\u5c42：\u8ba1\u7b97\u5404\u5c42\u5206\u6570，\u9009\u62e9\u5f97\u5206\u6700\u9ad8\u4e14 $\\\\ge 1.0$ \u7684\u5c42\u7ea7\u4f5c\u4e3a\u6e90\u5c42\u00a0start_level_，\u76ee\u6807\u5c42\u9ed8\u8ba4\u8bbe\u4e3a\u00a0output_level_ = start_level_ + 1（\u82e5\u6e90\u5c42\u4e3a L0，\u76ee\u6807\u5c42\u901a\u5e38\u4e3a Base Level）\u3002<\/p>\n<\/li>\n
\u6311\u9009\u6e90\u5c42\u5019\u9009\u6587\u4ef6：\u4f9d\u636e\u914d\u7f6e\u7684\u5019\u9009\u4f18\u5148\u7ea7\u00a0compaction_pri，\u5728\u6e90\u5c42\u9009\u51fa\u4e00\u4e2a\u6700\u9ad8\u4f18\u5148\u7ea7\u6587\u4ef6\u3002<\/p>\n<\/li>\n
\u6269\u5c55\u8fb9\u754c\u91cd\u53e0：\u82e5\u6240\u9009\u6587\u4ef6\u7684\u8fb9\u754c\u952e\u4e0e\u540c\u5c42\u5176\u4ed6\u6587\u4ef6\u7684\u8fb9\u754c\u952e\u5b58\u5728\u76f8\u540c UserKey，\u5fc5\u987b\u4e00\u5e76\u62c9\u5165，\u907f\u514d\u5c06\u76f8\u540c UserKey \u7684\u4e0d\u540c\u7248\u672c\u62c6\u5206\u81f3\u4e0d\u540c\u6587\u4ef6\u3002<\/p>\n<\/li>\n
\u83b7\u53d6\u76ee\u6807\u5c42\u91cd\u53e0\u6587\u4ef6：\u4f9d\u636e\u8f93\u5165\u6587\u4ef6\u7684\u603b\u952e\u8303\u56f4，\u8c03\u7528\u00a0vstorage_->GetOverlappingInputs()\u00a0\u5728\u76ee\u6807\u5c42\u68c0\u7d22\u5168\u90e8\u76f8\u4ea4\u6587\u4ef6\u3002<\/p>\n<\/li>\n
\u5c1d\u8bd5\u6279\u91cf\u8d2a\u5fc3\u6269\u5c55：\u82e5\u76ee\u6807\u5c42\u8fd4\u56de\u7684\u91cd\u53e0\u6587\u4ef6\u5217\u8868\u4e3a\u7a7a，\u8fdb\u5165\u00a0TryExtendNonL0TrivialMove\u00a0\u903b\u8f91，\u5c1d\u8bd5\u5411\u76f8\u90bb\u4e24\u4fa7\u6269\u5c55\u540c\u6837\u65e0\u76ee\u6807\u5c42\u91cd\u53e0\u7684\u6587\u4ef6\u3002<\/p>\n<\/li>\n
\u6700\u7ec8\u95e8\u7981\u88c1\u51b3：\u6784\u9020\u00a0Compaction\u00a0\u5bf9\u8c61\u540e，\u8c03\u7528\u6838\u5fc3\u5224\u5b9a\u63a5\u53e3\u00a0Compaction::IsTrivialMove()（\u4f4d\u4e8e\u00a0db\/compaction\/compaction.cc）\u6267\u884c\u4e00\u7968\u5426\u51b3\u6821\u9a8c\u3002<\/p>\n<\/li>\n
\u5728\u00a0db\/compaction\/compaction.cc\u00a0\u4e2d，Compaction::IsTrivialMove()\u00a0\u6784\u6210\u4e86\u8df3\u8fc7\u7269\u7406\u91cd\u5199\u7684\u7b2c\u4e00\u9053\u95e8\u7981\u3002\u8981\u6ee1\u8db3\u96f6\u62f7\u8d1d，\u9996\u5148\u5fc5\u987b\u4e25\u683c\u7b26\u5408\u4ee5\u4e0b\u56db\u9879\u57fa\u672c\u6761\u4ef6：<\/p>\n
C++<\/p>\n
if (!(start_level_ != output_level_ && num_input_levels() == 1 &&
\n input(0, 0)->fd.GetPathId() == output_path_id() &&
\n InputCompressionMatchesOutput())) {
\n return false;
\n}<\/p>\n
\u5728 RocksDB \u7684\u8bbe\u8ba1\u4e2d，\u5e38\u89c4\u8de8\u5c42\u5f52\u5e76\u7684\u8f93\u5165\u5c42\u7ea7\u6570\u91cf\u00a0num_input_levels()\u00a0\u4e3a 2：\u7d22\u5f15 0 \u4ee3\u8868\u6e90\u5c42\u8f93\u5165\u6587\u4ef6，\u7d22\u5f15 1 \u4ee3\u8868\u76ee\u6807\u5c42\u88ab\u62c9\u5165\u7684\u91cd\u53e0\u6587\u4ef6\u3002\u4ec5\u5f53\u76ee\u6807\u5c42\u68c0\u7d22\u5230\u7684\u76f8\u4ea4\u6587\u4ef6\u96c6\u5408\u4e3a\u7a7a\u65f6，\u8f93\u5165\u7ed3\u6784\u624d\u4e0d\u4f1a\u63a8\u5165\u7b2c\u4e8c\u5c42\u6570\u636e，\u6b64\u65f6\u00a0num_input_levels()\u00a0\u624d\u4e3a 1\u3002\u54ea\u6015\u76ee\u6807\u5c42\u4ec5\u6709\u4e00\u4e2a\u6587\u4ef6\u4e0e\u8f93\u5165\u6587\u4ef6\u5b58\u5728\u5355\u4e2a\u952e\u7684\u8fb9\u7f18\u91cd\u5408，\u8be5\u6587\u4ef6\u4e5f\u4f1a\u88ab\u62c9\u5165\u8f93\u5165\u96c6，\u5bfc\u81f4\u00a0num_input_levels()\u00a0\u53d8\u4e3a 2，\u96f6\u62f7\u8d1d\u5f53\u5373\u7ec8\u6b62\u3002<\/p>\n
\u5982\u679c\u6e90\u5c42\u4e3a L0，\u60c5\u51b5\u66f4\u4e3a\u4e25\u82db\u3002\u5e38\u89c4\u5199\u5165\u4e0b L0 \u6587\u4ef6\u4e92\u76f8\u4ea4\u53e0，\u82e5\u4ece L0 \u6311\u51fa\u6587\u4ef6 A（\u5728 L1 \u65e0\u91cd\u53e0），\u4f46 L0 \u4e2d\u5b58\u5728\u5237\u76d8\u66f4\u65e9\u7684\u6587\u4ef6 B \u4e14 B \u4e0e A \u7684\u952e\u8303\u56f4\u5b58\u5728\u4ea4\u96c6\u3002\u82e5\u5f3a\u884c\u628a A \u632a\u5165 L1 \u800c\u5c06 B \u7559\u5728 L0，\u7531\u4e8e\u8bfb\u67e5\u8be2\u6c38\u8fdc\u5148\u67e5 L0 \u518d\u67e5 L1，\u4f1a\u5bfc\u81f4\u7248\u672c\u53ef\u89c1\u6027\u88ab\u98a0\u5012，\u4ea7\u751f\u810f\u8bfb\u6216\u5df2\u5220\u6570\u636e\u590d\u6d3b\u3002<\/p>\n
\u56e0\u6b64\u6e90\u7801\u5728\u51fd\u6570\u5f00\u5934\u8bbe\u7f6e\u4e86\u9632\u5fa1\u95e8\u7981：<\/p>\n
C++<\/p>\n
if (start_level_ == 0 && input_vstorage_->level0_non_overlapping() == false &&
\n l0_files_might_overlap_) {
\n return false;
\n}<\/p>\n
\u53ea\u6709\u6574\u4e2a L0 \u5df2\u7ecf\u8fc7\u9a8c\u8bc1\u4e92\u4e0d\u91cd\u53e0，\u6216\u8005\u672c\u6b21\u9009\u51fa\u7684\u6587\u4ef6\u96c6\u80fd\u81ea\u8bc1\u5728 L0 \u5185\u5b8c\u5168\u72ec\u7acb，L0 \u624d\u80fd\u8d70\u96f6\u62f7\u8d1d\u3002\u5e38\u89c4\u5199\u5165\u8d1f\u8f7d\u4e0b，L0 \u5230 L1 \u7684\u5f52\u5e76\u51e0\u4e4e\u5747\u9700\u7269\u7406\u91cd\u5199\u3002<\/p>\n
\u5224\u5b9a\u5f0f\u4e2d\u7684\u00a0input(0, 0)->fd.GetPathId() == output_path_id()\u00a0\u5bf9\u5e94\u591a\u78c1\u76d8\u5b58\u50a8\u62d3\u6251（db_paths）\u3002\u82e5\u6d45\u5c42\u6302\u8f7d\u5728\u9ad8\u901f NVMe \u56fa\u6001\u786c\u76d8（Path 0），\u800c\u6df1\u5c42\u4f4d\u4e8e\u5927\u5bb9\u91cf\u673a\u68b0\u76d8\u6216\u7f51\u7edc\u5b58\u50a8（Path 1），\u5728\u64cd\u4f5c\u7cfb\u7edf\u5c42\u9762\u4e0d\u53ef\u80fd\u4ec5\u901a\u8fc7\u4fee\u6539\u5143\u6570\u636e\u8de8\u7269\u7406\u5377\u79fb\u52a8\u6587\u4ef6\u3002\u4e00\u65e6 Path ID \u4e0d\u5339\u914d，\u5fc5\u987b\u8d70\u7269\u7406\u6570\u636e\u590d\u5236\u901a\u9053\u3002<\/p>\n
\u82e5\u5404\u5c42\u914d\u7f6e\u4e86\u9636\u68af\u5f0f\u538b\u7f29\u7b56\u7565（\u4f8b\u5982\u6d45\u5c42\u4f7f\u7528\u8f7b\u91cf LZ4 \u6216\u4e0d\u538b\u7f29\u4ee5\u964d\u4f4e CPU \u5f00\u9500，\u6df1\u5c42\u4f7f\u7528\u9ad8\u538b\u7f29\u6bd4 ZSTD \u964d\u4f4e\u5b58\u50a8\u6210\u672c），\u5f53 L2 \u6587\u4ef6\u5c1d\u8bd5\u79fb\u52a8\u81f3 L3 \u65f6，\u5373\u4fbf\u76ee\u6807\u5c42\u5b8c\u5168\u65e0\u51b2\u7a81，InputCompressionMatchesOutput()\u00a0\u4e5f\u4f1a\u76f4\u63a5\u8fd4\u56de false\u3002\u56e0\u4e3a\u653e\u884c\u96f6\u62f7\u8d1d\u4f1a\u5bfc\u81f4\u672a\u538b\u7f29\u6216\u8f7b\u91cf\u538b\u7f29\u7684\u6570\u636e\u76f4\u63a5\u843d\u5165\u9ad8\u538b\u7f29\u6bd4\u5c42，\u7834\u574f\u4e86\u8be5\u5c42\u7684\u5b58\u50a8\u5bc6\u5ea6\u9884\u671f\u3002\u7cfb\u7edf\u5b81\u53ef\u8017\u8d39 I\/O \u8fdb\u884c\u8f6c\u7801\u91cd\u5199，\u4e5f\u7edd\u4e0d\u7834\u574f\u5206\u5c42\u538b\u7f29\u4e00\u81f4\u6027\u3002<\/p>\n
\u5373\u4fbf\u524d\u8ff0\u56db\u4e2a\u57fa\u7840\u95e8\u69db\u5168\u90e8\u901a\u8fc7，\u4f9d\u7136\u4e0d\u80fd\u76f4\u63a5\u6267\u884c\u96f6\u62f7\u8d1d\u3002\u5728\u00a0db\/compaction\/compaction.cc\u00a0\u4e2d，\u5b58\u5728\u4e00\u6bb5\u5173\u952e\u7684\u9632\u5fa1\u6027\u903b\u8f91\u2014\u2014\u7956\u7236\u5c42\u91cd\u53e0\u4f53\u79ef\u68c0\u67e5：<\/p>\n
C++<\/p>\n
if (output_level_ + 1 < number_levels_) {
\n std::unique_ptr<SstPartitioner> partitioner = CreateSstPartitioner();
\n for (const auto& file : inputs_.front().files) {
\n std::vector<FileMetaData*> file_grand_parents;
\n \/\/ \u83b7\u53d6\u8f93\u5165\u6587\u4ef6\u5728\u7956\u7236\u5c42（output_level_ + 1）\u4e2d\u7684\u76f8\u4ea4\u6587\u4ef6\u5217\u8868
\n input_vstorage_->GetOverlappingInputs(output_level_ + 1, &file->smallest,
\n &file->largest,
\n &file_grand_parents);
\n const auto compaction_size =
\n file->fd.GetFileSize() + TotalFileSize(file_grand_parents);
\n \/\/ \u82e5\u4e0e\u7956\u7236\u5c42\u91cd\u53e0\u7684\u603b\u6570\u636e\u91cf\u8d85\u8fc7 max_compaction_bytes，\u4e00\u7968\u5426\u51b3！
\n if (compaction_size > max_compaction_bytes_) {
\n return false;
\n }<\/p>\n
if (partitioner.get() != nullptr) {
\n if (!partitioner->CanDoTrivialMove(file->smallest.user_key(),
\n file->largest.user_key())) {
\n return false;
\n }
\n }
\n }
\n}<\/p>\n
\u5047\u8bbe\u5f53\u524d\u5f85\u5f52\u5e76\u6587\u4ef6\u4f4d\u4e8e L2，\u5927\u5c0f\u4e3a 64 MB；\u76ee\u6807\u5c42 L3 \u5728\u5bf9\u5e94\u952e\u8303\u56f4\u5b8c\u5168\u4e3a\u7a7a，\u770b\u4f3c\u662f\u5b8c\u7f8e\u7684\u96f6\u62f7\u8d1d\u573a\u666f\u3002\u7136\u800c，\u8c03\u5ea6\u5668\u987a\u7740\u952e\u8303\u56f4\u5411\u6df1\u5c42\u7684 L4（\u5373\u5f53\u524d\u5f52\u5e76\u7684\u7956\u7236\u5c42）\u68c0\u7d22\u65f6，\u53d1\u73b0\u8be5\u952e\u533a\u95f4\u5728 L4 \u5b58\u5728\u5bc6\u96c6\u7684\u5df2\u6709\u6570\u636e，\u6587\u4ef6\u603b\u8ba1\u8fbe\u5230\u6570\u5341\u4e2a\u3001\u7d2f\u8ba1\u5927\u5c0f\u8d85\u8fc7 1 GB\u3002<\/p>\n
\u82e5\u6b64\u65f6\u653e\u884c\u96f6\u62f7\u8d1d，\u8fd9\u9897 64 MB \u7684\u6587\u4ef6\u5c06\u88ab\u76f4\u63a5\u7a7a\u6295\u5230 L3\u3002\u7531\u4e8e\u5176\u952e\u8de8\u5ea6\u5f88\u5927，\u5728\u672a\u6765\u8be5\u6587\u4ef6\u4ece L3 \u89e6\u53d1\u4e0b\u6c89\u65f6，\u5fc5\u987b\u5c06 L4 \u8fd9\u8d85\u8fc7 1 GB \u7684\u6570\u636e\u5168\u90e8\u5377\u5165\u540c\u4e00\u573a\u5f52\u5e76\u4efb\u52a1，\u77ac\u95f4\u5f15\u7206\u8d85\u5927\u578b Compaction，\u4e25\u91cd\u963b\u585e\u540e\u53f0\u5e76\u6076\u5316\u524d\u53f0\u5ef6\u8fdf\u3002<\/p>\n
\u76f8\u53cd，\u82e5\u5728 L2 \u9636\u6bb5\u62d2\u7edd\u96f6\u62f7\u8d1d\u5e76\u6267\u884c\u5e38\u89c4\u5f52\u5e76，\u540e\u53f0\u6392\u5e8f\u91cd\u5199\u4f1a\u5c06\u8fd9 64 MB \u6570\u636e\u5408\u7406\u5207\u7ec6\u4e3a\u7b26\u5408 L3 \u89c4\u683c\u7684\u66f4\u5c0f\u7c92\u5ea6\u6587\u4ef6\u3002\u540e\u7eed\u8fd9\u4e9b\u7ec6\u7c92\u5ea6\u6587\u4ef6\u72ec\u7acb\u5411\u4e0b\u5f52\u5e76\u65f6，\u6bcf\u6b21\u4e0e L4 \u78b0\u649e\u7684\u6570\u636e\u91cf\u5747\u5904\u4e8e\u53ef\u63a7\u8303\u56f4\u3002<\/p>\n
\u901a\u8fc7\u00a0compaction_size > max_compaction_bytes_\u00a0\u5b9e\u65bd\u62e6\u622a，\u672c\u8d28\u4e0a\u662f\u7528\u6d45\u5c42\u4e00\u6b21\u53ef\u63a7\u7684\u7269\u7406\u91cd\u5199，\u907f\u514d\u5728\u6df1\u5c42\u5f15\u7206\u5931\u63a7\u7684\u7ea7\u8054\u5f52\u5e76\u98ce\u66b4\u3002<\/p>\n
\u5728\u66f4\u590d\u6742\u7684\u90e8\u7f72\u573a\u666f\u4e2d，\u8fd8\u5b58\u5728\u4ee5\u4e0b\u51e0\u7c7b\u76f4\u63a5\u5426\u51b3\u96f6\u62f7\u8d1d\u7684\u89c4\u5219：<\/p>\n
SstPartitioner \u8fb9\u754c\u7ea6\u675f：\u82e5\u7cfb\u7edf\u914d\u7f6e\u4e86\u5206\u533a\u5668\u7528\u4e8e\u6309\u7279\u5b9a\u524d\u7f00\u5207\u5206\u6587\u4ef6，\u5f53\u8f93\u5165\u6587\u4ef6\u7684\u00a0smallest\u00a0\u4e0e\u00a0largest\u00a0\u8de8\u8d8a\u4e86\u5206\u533a\u65ad\u70b9，\u76f4\u63a5\u642c\u79fb\u4f1a\u7834\u574f\u76ee\u6807\u5c42\u7684\u7269\u7406\u5207\u5206\u89c4\u8303\u3002\u6b64\u65f6\u00a0partitioner->CanDoTrivialMove()\u00a0\u8fd4\u56de false，\u5f3a\u5236\u7269\u7406\u91cd\u5199\u4ee5\u4fbf\u6309\u65ad\u70b9\u91cd\u65b0\u62c6\u5206\u6587\u4ef6\u3002<\/p>\n<\/li>\n
\u6309\u952e\u5206\u5c42\u653e\u7f6e（PerKeyPlacement）：\u8be5\u7279\u6027\u5141\u8bb8\u5728\u5355\u6b21\u5f52\u5e76\u4e2d\u6839\u636e key \u7684\u65f6\u6548\u6216\u51b7\u70ed\u5c5e\u6027，\u5c06\u90e8\u5206 key \u7559\u5728\u6d45\u5c42\u3001\u90e8\u5206\u6c89\u5165\u6df1\u5c42\u3002\u7531\u4e8e\u8fd9\u9700\u8981\u7ec6\u5316\u5230\u5355\u4e2a KV \u8bb0\u5f55\u8fdb\u884c\u89e3\u5305\u5206\u6d41，\u4e0e\u201c\u6574\u6587\u4ef6\u5143\u6570\u636e\u53d8\u66f4\u201d\u5929\u7136\u4e92\u65a5，\u4e00\u65e6\u5f00\u542f\u76f4\u63a5\u7981\u7528\u96f6\u62f7\u8d1d\u3002<\/p>\n<\/li>\n
CompactionFilter \u4e0e\u6e29\u5ea6\u8fc1\u79fb：\u82e5\u914d\u7f6e\u4e86\u5fc5\u9009\u7684 CompactionFilter，\u7531\u4e8e\u9700\u8981\u9010\u6761\u8fc7\u6ee4\u8fc7\u671f\u8bb0\u5f55，\u6216\u8005\u5f52\u5e76\u539f\u56e0\u4e3a\u5b58\u50a8\u6e29\u5ea6\u53d8\u66f4（kChangeTemperature，\u9700\u5728\u4e0d\u540c\u4ecb\u8d28\u95f4\u91cd\u65b0\u5199\u5165\u6570\u636e\u5757），\u5747\u4f1a\u5f3a\u5236\u6267\u884c\u5168\u91cf\u7269\u7406\u5f52\u5e76\u3002<\/p>\n<\/li>\n<\/ul>\n
\u7efc\u5408\u4e0a\u8ff0\u7ea6\u675f，RocksDB \u5224\u65ad\u4e00\u6b21\u8de8\u5c42\u5f52\u5e76\u80fd\u5426\u8d70\u96f6\u62f7\u8d1d\u7684\u5b8c\u6574\u903b\u8f91\u5982\u4e0b\u56fe\u6240\u793a：<\/p>\n
text<\/p>\n
[PickCompaction \u9009\u51fa\u5019\u9009\u6587\u4ef6\u96c6]
\n |
\n v
\n [\u76ee\u6807\u5c42\u662f\u5426\u6709\u91cd\u53e0\u6587\u4ef6?] ———— \u662f ————> [\u8d70\u5411\u5168\u91cf\u7269\u7406\u91cd\u5199]
\n | \u5426
\n v
\n [L0 \u6587\u4ef6\u53ef\u80fd\u5b58\u5728\u91cd\u53e0?] ———— \u662f ————> [\u8d70\u5411\u5168\u91cf\u7269\u7406\u91cd\u5199]
\n | \u5426
\n v
\n [\u6e90\u8def\u5f84\u4e0e\u76ee\u6807\u8def\u5f84\u4e00\u81f4?] ———— \u5426 ————> [\u8d70\u5411\u5168\u91cf\u7269\u7406\u91cd\u5199]
\n | \u662f
\n v
\n [\u5404\u5c42\u538b\u7f29\u7b97\u6cd5\u5b8c\u5168\u5339\u914d?] ———— \u5426 ————> [\u8d70\u5411\u5168\u91cf\u7269\u7406\u91cd\u5199]
\n | \u662f
\n v
\n [\u7956\u7236\u5c42\u91cd\u53e0\u8d85 max_compaction_bytes?] – \u662f ———-> [\u8d70\u5411\u5168\u91cf\u7269\u7406\u91cd\u5199]
\n | \u5426
\n v
\n [\u5206\u533a\u5668 \/ Filter \/ \u6e29\u5ea6\u68c0\u67e5\u901a\u8fc7?] — \u5426 ————> [\u8d70\u5411\u5168\u91cf\u7269\u7406\u91cd\u5199]
\n | \u662f
\n v
\n [\u6279\u51c6\u96f6\u62f7\u8d1d\u642c\u79fb IsTrivialMove]<\/p>\n
\u57fa\u4e8e RocksDB \u5355\u5143\u6d4b\u8bd5\u5957\u4ef6（CompactionPickerTest），\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7\u7cbe\u786e\u6784\u9020\u8fb9\u754c\u6761\u4ef6\u6765\u590d\u73b0\u96f6\u62f7\u8d1d\u7684\u89e6\u53d1\u4e0e\u9000\u5316\u884c\u4e3a\u3002<\/p>\n
\u5728\u6d4b\u8bd5\u5957\u4ef6\u4e2d\u521d\u59cb\u5316\u4e00\u4e2a 6 \u5c42\u7684 Leveled \u5b58\u50a8\u6a21\u578b，\u6838\u5fc3\u53c2\u6570\u5982\u4e0b：<\/p>\n
max_bytes_for_level_base = 1000u（\u5355\u5c42\u5bb9\u91cf\u57fa\u51c6）；<\/p>\n<\/li>\n
max_compaction_bytes = 10000001u（\u653e\u5927\u5f52\u5e76\u9608\u503c，\u89c4\u907f\u7956\u7236\u5c42\u5bb9\u91cf\u8bef\u4f24）；<\/p>\n<\/li>\n
\u7edf\u4e00\u5404\u5c42\u538b\u7f29\u4e3a\u672a\u538b\u7f29，\u5355\u6302\u8f7d\u70b9\u5355\u4e00\u8def\u5f84；<\/p>\n<\/li>\n
\u5019\u9009\u4f18\u5148\u7ea7\u8bbe\u5b9a\u4e3a\u00a0kMinOverlappingRatio\u3002<\/p>\n<\/li>\n<\/ul>\n
\u5728 L2 \u6784\u9020 8 \u4e2a\u8fde\u7eed\u6587\u4ef6，\u5728 L3 \u523b\u610f\u4fdd\u7559\u00a0[300, 700]\u00a0\u7684\u771f\u7a7a\u533a\u95f4：<\/p>\n
C++<\/p>\n
TEST_F(CompactionPickerTest, TraceTrivialMoveVerification) {
\n mutable_cf_options_.max_bytes_for_level_base = 1000u;
\n mutable_cf_options_.max_compaction_bytes = 10000001u;
\n ioptions_.level_compaction_dynamic_level_bytes = false;
\n ioptions_.compaction_pri = kMinOverlappingRatio;
\n NewVersionStorage(6, kCompactionStyleLevel);<\/p>\n
\/\/ \u5728 L2 \u6784\u9020 8 \u4e2a\u8fde\u7eed\u6587\u4ef6，\u5404\u7ea6 3000 \u5b57\u8282
\n Add(2, 1U, "100", "150", 3000U);
\n Add(2, 2U, "151", "200", 3001U);
\n Add(2, 3U, "301", "350", 3000U);
\n Add(2, 4U, "351", "400", 3000U);
\n Add(2, 5U, "451", "500", 3000U);
\n Add(2, 6U, "551", "600", 3000U);
\n Add(2, 7U, "651", "700", 3000U);
\n Add(2, 8U, "851", "900", 3000U);<\/p>\n
\/\/ \u5728 L3 \u6784\u9020\u5df2\u6709\u6587\u4ef6，\u6ce8\u610f\u4e2d\u95f4 [300, 700] \u533a\u95f4\u4fdd\u6301\u5b8c\u5168\u771f\u7a7a
\n Add(3, 15U, "120", "130", 700U); \/\/ \u4e0e L2 \u6587\u4ef6 1 \u91cd\u53e0
\n Add(3, 16U, "170", "180", 700U); \/\/ \u4e0e L2 \u6587\u4ef6 2 \u91cd\u53e0
\n Add(3, 17U, "220", "230", 700U); \/\/ \u4f4d\u4e8e\u95f4\u9694\u533a
\n Add(3, 18U, "870", "880", 700U); \/\/ \u4e0e L2 \u6587\u4ef6 8 \u91cd\u53e0<\/p>\n
UpdateVersionStorageInfo();<\/p>\n
std::unique_ptr<Compaction> compaction(level_compaction_picker.PickCompaction(
\n cf_name_, mutable_cf_options_, mutable_db_options_,
\n \/*existing_snapshots=*\/{}, \/* snapshot_checker *\/ nullptr,
\n vstorage_.get(), &log_buffer_, \/*full_history_ts_low=*\/""));<\/p>\n
ASSERT_NE(compaction, nullptr);
\n \/\/ \u65ad\u8a00\u4e00：\u6210\u529f\u88c1\u5b9a\u4e3a\u96f6\u62f7\u8d1d\u642c\u79fb
\n ASSERT_TRUE(compaction->IsTrivialMove());
\n \/\/ \u65ad\u8a00\u4e8c：\u76ee\u6807\u5c42\u65e0\u76f8\u4ea4\u6587\u4ef6，\u8f93\u5165\u5c42\u6570\u4e25\u683c\u4e3a 1
\n ASSERT_EQ(1, compaction->num_input_levels());
\n \/\/ \u65ad\u8a00\u4e09：\u89e6\u53d1\u6279\u91cf\u6269\u5c55，\u4e00\u6b21\u6027\u6253\u5305 4 \u4e2a\u6587\u4ef6
\n ASSERT_EQ(4, compaction->num_input_files(0));
\n ASSERT_EQ(3, compaction->input(0, 0)->fd.GetNumber());
\n ASSERT_EQ(4, compaction->input(0, 1)->fd.GetNumber());
\n ASSERT_EQ(5, compaction->input(0, 2)->fd.GetNumber());
\n ASSERT_EQ(6, compaction->input(0, 3)->fd.GetNumber());
\n}<\/p>\n
\u6d4b\u8bd5\u65ad\u8a00\u987a\u5229\u901a\u8fc7\u3002\u6267\u884c\u7ec6\u8282\u8868\u660e：<\/p>\n
\u6587\u4ef6 1 \u4e0e 2 \u5728 L3 \u5b58\u5728\u91cd\u53e0，\u800c\u6587\u4ef6 3 \u81f3 6 \u5728 L3 \u7684\u91cd\u53e0\u5b57\u8282\u6570\u5747\u4e3a 0\u3002\u57fa\u4e8e\u00a0kMinOverlappingRatio，\u6587\u4ef6 3 \u7684\u91cd\u53e0\u6bd4\u6700\u4f4e（\u4e3a 0），\u56e0\u800c\u6700\u5148\u88ab\u9009\u4e2d\u3002<\/p>\n<\/li>\n
\u968f\u540e\u00a0TryExtendNonL0TrivialMove\u00a0\u987a\u7740\u952e\u987a\u5e8f\u5411\u53f3\u63a2\u6d4b，\u53d1\u73b0\u76f8\u90bb\u7684\u6587\u4ef6 4\u30015\u30016 \u5728 L3 \u540c\u6837\u6ca1\u6709\u91cd\u53e0，\u4e14\u603b\u5927\u5c0f\u672a\u8d85\u6807\u3002<\/p>\n<\/li>\n
\u6700\u7ec8\u5355\u6b21\u6253\u5305 4 \u4e2a\u6587\u4ef6\u6574\u4f53\u4e0b\u6c89\u3002\u6574\u4e2a\u8fc7\u7a0b\u4ea7\u751f\u7684\u7269\u7406\u8bfb\u5199\u4e3a 0 \u5b57\u8282，\u5143\u6570\u636e\u53d8\u66f4\u76f4\u63a5\u63a8\u8fdb\u4e86 12 KB \u6570\u636e\u3002<\/p>\n<\/li>\n
\u5728\u573a\u666f A \u7684\u57fa\u7840\u4e0a，\u6211\u4eec\u4ec5\u5411 L3 \u539f\u672c\u771f\u7a7a\u7684\u533a\u95f4\u6ce8\u5165\u4e00\u4e2a\u4ec5 100 \u5b57\u8282\u7684\u5fae\u578b\u6587\u4ef6，\u5176\u4f59\u6570\u636e\u4fdd\u6301\u4e0d\u53d8：<\/p>\n
C++<\/p>\n
\/\/ \u4ec5\u5728 L3 \u63d2\u5165\u4e00\u4e2a 100 \u5b57\u8282\u7684\u5c0f\u6587\u4ef6，\u8303\u56f4\u4e3a [340, 345]
\n Add(3, 99U, "340", "345", 100U);
\n UpdateVersionStorageInfo();<\/p>\n
std::unique_ptr<Compaction> compaction(level_compaction_picker.PickCompaction(
\n cf_name_, mutable_cf_options_, mutable_db_options_,
\n \/*existing_snapshots=*\/{}, \/* snapshot_checker *\/ nullptr,
\n vstorage_.get(), &log_buffer_, \/*full_history_ts_low=*\/""));<\/p>\n
ASSERT_NE(compaction, nullptr);
\n \/\/ \u96f6\u62f7\u8d1d\u6761\u4ef6\u88ab\u5b8c\u5168\u7834\u574f
\n ASSERT_FALSE(compaction->IsTrivialMove());
\n \/\/ \u8f93\u5165\u5c42\u7ea7\u6570\u53d8\u4e3a 2
\n ASSERT_EQ(2, compaction->num_input_levels());<\/p>\n
\u8fd0\u884c\u7ed3\u679c\u663e\u793a\u00a0compaction->IsTrivialMove()\u00a0\u7acb\u5373\u8fd4\u56de false\u3002<\/p>\n
\u8fd9\u662f\u56e0\u4e3a\u6587\u4ef6 99 \u7684\u952e\u533a\u95f4\u00a0[340, 345]\u00a0\u6070\u597d\u5d4c\u5165\u4e86 L2 \u6587\u4ef6 3 \u7684\u8303\u56f4\u00a0[301, 350]\u00a0\u5185\u3002\u5373\u4fbf\u53ea\u6709 100 \u5b57\u8282，\u8c03\u5ea6\u5668\u5728\u62c9\u53d6\u76ee\u6807\u5c42\u91cd\u53e0\u65f6\u4e5f\u5fc5\u987b\u628a\u6587\u4ef6 99 \u7eb3\u5165\u8f93\u5165\u96c6：<\/p>\n
num_input_levels()\u00a0\u4ece 1 \u53d8\u4e3a 2；<\/p>\n<\/li>\n
\u540e\u53f0\u7ebf\u7a0b\u5fc5\u987b\u5b8c\u6574\u8bfb\u5165 L2 \u6587\u4ef6 3（3000 \u5b57\u8282）\u4e0e L3 \u6587\u4ef6 99（100 \u5b57\u8282）；<\/p>\n<\/li>\n
\u7ecf\u7531\u591a\u8def\u8fed\u4ee3\u5668\u91cd\u65b0\u6392\u5e8f\u6bd4\u5bf9，\u91cd\u65b0\u5199\u51fa 3100 \u5b57\u8282\u7684\u65b0\u6587\u4ef6\u3002<\/p>\n<\/li>\n<\/ul>\n
\u5fae\u5c0f\u7684\u91cd\u53e0\u8fb9\u754c\u6253\u7834\u4e86\u771f\u7a7a\u533a\u95f4，\u4f7f\u539f\u672c\u51e0\u5341\u5fae\u79d2\u7684\u5143\u6570\u636e\u4fee\u6539\u76f4\u63a5\u9000\u5316\u4e3a\u4e86\u5168\u91cf\u78c1\u76d8\u7269\u7406 I\/O\u3002<\/p>\n
\u5728\u573a\u666f A \u4e2d，\u6587\u4ef6 3 \u81f3 7 \u5728 L3 \u5747\u65e0\u91cd\u53e0，\u4f46\u6700\u7ec8\u53ea\u6253\u5305\u4e86 4 \u4e2a\u6587\u4ef6\u3002\u8fd9\u662f\u7531\u00a0TryExtendNonL0TrivialMove（\u4f4d\u4e8e\u00a0compaction_picker_level.cc）\u4e2d\u7684\u786c\u7f16\u7801\u4e0a\u9650\u51b3\u5b9a\u7684：<\/p>\n
C++<\/p>\n
const size_t kMaxMultiTrivialMove = 4;
\n\/\/ …
\nfor (int i = start_index + 1;
\n i < static_cast<int>(level_files.size()) &&
\n start_level_inputs_.size() < kMaxMultiTrivialMove;
\n i++) {
\n FileMetaData* next_file = level_files[i];
\n if (next_file->being_compacted) {
\n break; \/\/ \u76f8\u90bb\u6587\u4ef6\u82e5\u88ab\u5176\u4ed6\u5f52\u5e76\u7ebf\u7a0b\u5360\u7528，\u7acb\u5373\u7ec8\u6b62\u6269\u5c55
\n }
\n \/\/ \u6821\u9a8c\u6269\u5c55\u540e\u7684\u603b\u952e\u8303\u56f4\u5728\u76ee\u6807\u5c42\u662f\u5426\u4f9d\u7136\u65e0\u4ea4\u53e0
\n vstorage_->GetOverlappingInputs(output_level_, &(initial_file->smallest),
\n &(next_file->largest),
\n &output_level_inputs.files);
\n if (!output_level_inputs.empty()) {
\n break; \/\/ \u4e00\u65e6\u53d1\u73b0\u91cd\u53e0，\u7acb\u5373\u505c\u6b62
\n }
\n \/\/ \u7d2f\u52a0\u5927\u5c0f\u4e0d\u5f97\u8d85\u8fc7 max_compaction_bytes
\n total_size += next_file->fd.GetFileSize();
\n if (total_size > mutable_cf_options_.max_compaction_bytes) {
\n break;
\n }
\n start_level_inputs_.files.push_back(next_file);
\n}<\/p>\n
\u5355\u6b21\u6700\u591a\u6269\u5c55 4 \u4e2a\u6587\u4ef6\u7684\u9650\u5236，\u662f\u4e3a\u4e86\u9632\u6b62\u4e00\u6b21\u6027\u5c06\u8fc7\u5bbd\u952e\u533a\u95f4\u7684\u8fde\u7eed\u6587\u4ef6\u96c6\u4f53\u4e0b\u6c89，\u907f\u514d\u5728\u76ee\u6807\u5c42\u5f62\u6210\u5927\u9762\u79ef\u7684\u8fde\u7eed\u6587\u4ef6\u5e26，\u4ece\u800c\u52a0\u5927\u8be5\u533a\u95f4\u4e0e\u66f4\u6df1\u5c42\u7ea7\u53d1\u751f\u5e76\u53d1\u51b2\u7a81\u4e0e\u8d85\u5927\u5f52\u5e76\u7684\u6982\u7387\u3002<\/p>\n
\u5728 Leveled Compaction \u67b6\u6784\u4e2d，\u5168\u5e93\u7684\u603b\u5199\u653e\u5927\u7406\u8bba\u4e0a\u662f\u5404\u5c42\u5c40\u90e8\u5199\u653e\u5927\u7684\u7d2f\u52a0：<\/p>\n
$$\\\\text{WA}{\\\\text{total}} \\\\approx 1 + \\\\sum{i=0}^{N-1} \\\\text{WA}{L_i \\\\to L{i+1}}$$<\/p>\n
\u82e5\u5355\u6b21\u8de8\u5c42\u538b\u5b9e\u6ee1\u8db3\u4e86\u96f6\u62f7\u8d1d\u642c\u79fb，\u7531\u4e8e\u5199\u5165\u78c1\u76d8\u7269\u7406\u5b57\u8282\u6570\u4e3a 0，\u8fd9\u4e00\u6b65\u7684\u5c40\u90e8\u5199\u653e\u5927\u76f4\u63a5\u4e3a 0\u3002<\/p>\n
\u82e5\u5355\u8c03\u9012\u589e\u7684\u6279\u6b21\u6570\u636e\u80fd\u591f\u5728\u6d45\u5c42\u8fde\u7eed\u89e6\u53d1 Trivial Move \u5e76\u987a\u5229\u6ed1\u843d\u81f3\u6df1\u5c42，\u6d45\u5c42\u5199\u653e\u5927\u5c06\u88ab\u5b8c\u5168\u62b9\u5e73，\u53ea\u6709\u5f53\u5b83\u6700\u7ec8\u5728\u6df1\u5c42\u78b0\u649e\u5230\u5b58\u91cf\u6570\u636e\u65f6\u624d\u5f00\u59cb\u6d88\u8017\u7269\u7406 I\/O\u3002<\/p>\n
\u7136\u800c，\u96f6\u62f7\u8d1d\u642c\u79fb\u5e76\u4e0d\u9002\u7528\u4e8e\u6240\u6709\u573a\u666f，\u5b83\u672c\u8d28\u4e0a\u662f\u7528\u201c\u7a7a\u95f4\u5229\u7528\u7387\u4e0b\u964d\u201d\u4e0e\u201c\u8bfb\u6027\u80fd\u6298\u635f\u201d\u6362\u53d6\u5199\u5165\u541e\u5410\u7684\u77ed\u5e73\u5feb\u624b\u6bb5：<\/p>\n
\u7269\u7406\u5f52\u5e76\u7684\u6838\u5fc3\u529f\u80fd\u662f\u5783\u573e\u56de\u6536\u3002\u5f53\u4e0a\u5c42\u4ea7\u751f Delete \u64cd\u4f5c\u65f6，\u5e95\u5c42\u4ec5\u662f\u5199\u5165\u4e00\u6761\u5893\u7891\u8bb0\u5f55\u3002\u8981\u5f7b\u5e95\u62b9\u9664\u8bb0\u5f55\u5e76\u91ca\u653e\u78c1\u76d8\u7a7a\u95f4，\u5fc5\u987b\u901a\u8fc7\u7269\u7406\u5f52\u5e76\u5c06\u5176\u4e0e\u6df1\u5c42\u65e7\u7248\u672c\u6570\u636e\u5bf9\u9f50\u6d88\u9664\u3002<\/p>\n
\u96f6\u62f7\u8d1d\u642c\u79fb\u5b8c\u5168\u4e0d\u89e6\u78b0 SSTable \u6570\u636e\u5757\u3002\u82e5\u5305\u542b\u5927\u91cf\u5893\u7891\u7684\u6587\u4ef6\u9891\u7e41\u6267\u884c\u96f6\u62f7\u8d1d，\u8fd9\u4e9b\u5893\u7891\u5c06\u539f\u5c01\u4e0d\u52a8\u5730\u6c89\u5165\u6df1\u5c42\u3002\u66f4\u4e25\u91cd\u7684\u662f，\u6e90\u5c42\u88ab\u8986\u76d6\u5199\u7684\u65e7\u7248\u672c\u6570\u636e\u4e5f\u65e0\u6cd5\u88ab\u5254\u9664，\u5bfc\u81f4\u78c1\u76d8\u7a7a\u95f4\u957f\u671f\u65e0\u6cd5\u91ca\u653e，\u7a7a\u95f4\u653e\u5927（Space Amplification）\u663e\u8457\u6076\u5316\u3002<\/p>\n
\u5728\u70b9\u67e5\u4e0e\u8303\u56f4\u904d\u5386\u4e2d，\u5e03\u9686\u8fc7\u6ee4\u5668\u4e0e\u8fed\u4ee3\u5668\u7684\u6267\u884c\u5f00\u9500\u9ad8\u5ea6\u4f9d\u8d56\u4e8e\u5404\u5c42\u6587\u4ef6\u7684\u5e73\u5747\u5c3a\u5bf8\u4e0e\u5206\u5e03\u81f4\u5bc6\u6027\u3002<\/p>\n
\u5e38\u89c4\u7269\u7406\u5f52\u5e76\u4f1a\u5c06\u96f6\u6563\u6570\u636e\u91cd\u65b0\u7ec4\u88c5\u4e3a\u7b26\u5408\u9884\u8bbe\u5927\u5c0f（\u4f8b\u5982 64 MB）\u7684\u89c4\u8303 SSTable\u3002\u4f46\u96f6\u62f7\u8d1d\u642c\u79fb\u4f1a\u5c06\u6d45\u5c42\u5c3a\u5bf8\u504f\u5c0f（\u5982\u521a Flush \u51fa\u7684\u7ec6\u788e\u6587\u4ef6）\u76f4\u63a5\u539f\u6837\u6302\u8f7d\u5230\u6df1\u5c42，\u5bfc\u81f4\u6df1\u5c42\u6587\u4ef6\u6570\u91cf\u66b4\u589e\u3001\u952e\u8303\u56f4\u9ad8\u5ea6\u788e\u7247\u5316\u3002\u5728\u6267\u884c\u8303\u56f4\u626b\u63cf\u65f6，\u8fed\u4ee3\u5668\u5fc5\u987b\u5728\u6df1\u5c42\u5f52\u5e76\u66f4\u591a\u5c0f\u6587\u4ef6\u7684\u5806\u9876，\u589e\u52a0 CPU Cache Miss；\u800c\u6cbf\u9014\u672a\u88ab\u6e05\u7406\u7684\u5927\u91cf\u5893\u7891\u4e5f\u4f1a\u8feb\u4f7f\u626b\u63cf\u7ebf\u7a0b\u6267\u884c\u5927\u91cf\u65e0\u610f\u4e49\u7684\u8df3\u8dc3\u8fed\u4ee3，\u5f15\u53d1\u957f\u5c3e\u8bfb\u5ef6\u8fdf\u6296\u52a8\u3002<\/p>\n
\u5f53\u67d0\u4e00\u5c42\u7684\u603b\u6570\u636e\u91cf\u8d85\u6807\u89e6\u53d1 Compaction，\u4f46\u540c\u5c42\u5b58\u5728\u591a\u4e2a\u5019\u9009\u6587\u4ef6\u65f6，\u8c03\u5ea6\u5668\u5982\u4f55\u51b3\u5b9a\u4f18\u5148\u9009\u53d6\u54ea\u4e00\u4e2a？\u8fd9\u5c31\u662f\u914d\u7f6e\u53c2\u6570\u00a0compaction_pri\u00a0\u7684\u6838\u5fc3\u804c\u8d23\u3002<\/p>\n
\u5728 LevelDB \u4e2d，\u540c\u5c42\u6587\u4ef6\u7684\u9009\u62e9\u76f8\u5bf9\u7c97\u7cd9：\u7cfb\u7edf\u5728\u5185\u5b58\u4e2d\u4e3a\u6bcf\u4e00\u5c42\u8bb0\u5f55\u4e00\u4e2a\u6301\u4e45\u6e38\u6807（compact_pointer_）\u3002\u6bcf\u6b21\u5f52\u5e76\u5b8c\u6210\u540e，\u6e38\u6807\u63a8\u8fdb\u5230\u521a\u624d\u88ab\u5f52\u5e76\u6587\u4ef6\u7684\u6700\u5927\u952e\u5904\u3002\u4e0b\u6b21\u89e6\u53d1\u5f52\u5e76\u65f6，\u76f4\u63a5\u6cbf\u7740\u6e38\u6807\u4f4d\u7f6e\u540e\u79fb\u9009\u53d6\u4e0b\u4e00\u4e2a\u6587\u4ef6\u3002<\/p>\n
\u5728\u5355\u7ebf\u7a0b\u5f52\u5e76\u7684\u65f6\u4ee3，\u8fd9\u79cd\u5168\u5c40\u8f6e\u8f6c\u80fd\u4fdd\u8bc1\u5404\u952e\u533a\u95f4\u88ab\u5747\u5300\u538b\u5b9e\u3002\u4f46\u8fdb\u5165\u591a\u7ebf\u7a0b\u5e76\u53d1\u5f52\u5e76\u540e，\u5355\u6e38\u6807\u8f6e\u8f6c\u66b4\u9732\u51fa\u660e\u663e\u7f3a\u9677：<\/p>\n
\u4e25\u91cd\u7684\u5e76\u53d1\u9501\u51b2\u7a81：\u591a\u4e2a\u5de5\u4f5c\u7ebf\u7a0b\u540c\u65f6\u83b7\u53d6\u6e38\u6807\u9644\u8fd1\u7684\u76f8\u90bb\u6587\u4ef6，\u5bfc\u81f4\u5e76\u53d1\u5f52\u5e76\u4efb\u52a1\u6781\u6613\u56e0\u952e\u8303\u56f4\u4ea4\u53e0\u800c\u4e92\u76f8\u963b\u585e；<\/p>\n<\/li>\n
\u65e0\u89c6\u6570\u636e\u51b7\u70ed\u503e\u659c：\u73b0\u5b9e\u4e2d\u5199\u5165\u5f80\u5f80\u4e0d\u5747\u5300，\u76f2\u76ee\u8f6e\u8f6c\u4f1a\u5bfc\u81f4\u51b7\u6570\u636e\u533a\u95f4\u88ab\u9891\u7e41\u8c03\u5ea6，\u6d6a\u8d39 I\/O \u541e\u5410；<\/p>\n<\/li>\n
\u65e0\u6cd5\u5bf9\u5199\u653e\u5927\u5b9e\u65bd\u7cbe\u7ec6\u8c03\u4f18：\u4e0d\u540c\u6587\u4ef6\u7684\u76ee\u6807\u5c42\u91cd\u53e0\u5ea6\u5dee\u5f02\u5de8\u5927，\u673a\u68b0\u6309\u6e38\u6807\u9009\u62e9\u5bb9\u6613\u649e\u4e0a\u91cd\u53e0\u5de8\u5927\u7684\u6587\u4ef6\u3002<\/p>\n<\/li>\n<\/ul>\n
RocksDB \u4e3a\u6b64\u91cd\u6784\u4e86\u8c03\u5ea6\u6846\u67b6，\u63d0\u4f9b\u4e86\u57fa\u4e8e\u591a\u7ef4\u6307\u6807\u7684\u5019\u9009\u4f18\u5148\u7ea7\u673a\u5236\u3002<\/p>\n
\u5b98\u65b9\u5728\u300aOption of Compaction Priority\u300b\u67b6\u6784\u5206\u6790\u4e2d\u6307\u51fa\u4e86\u5f71\u54cd\u5199\u653e\u5927\u7684\u4e09\u5927\u5173\u952e\u53d8\u91cf：<\/p>\n
\u952e\u5bc6\u5ea6\u4e0e\u7a7a\u95f4\u7a7a\u6d1e：\u521a\u88ab\u5f52\u5e76\u8fc7\u7684\u533a\u57df\u901a\u5e38\u4f1a\u5f62\u6210\u952e\u5bc6\u5ea6\u8f83\u4f4e\u7684\u7a7a\u6d1e\u3002\u82e5\u4f18\u5148\u9009\u62e9\u952e\u8303\u56f4\u8de8\u5ea6\u5927\u3001\u5bc6\u5ea6\u4f4e\u7684\u6587\u4ef6，\u5176\u5728\u76ee\u6807\u5c42\u76f8\u4ea4\u7684\u6587\u4ef6\u5f80\u5f80\u66f4\u591a\u3002\u540c\u6837\u5927\u5c0f\u7684\u6587\u4ef6，\u82e5\u4e0e\u4e0b\u5c42 8 \u4e2a\u6587\u4ef6\u91cd\u53e0\u9700\u91cd\u5199 8 \u500d\u6570\u636e，\u82e5\u4e0e 12 \u4e2a\u6587\u4ef6\u91cd\u53e0\u5219\u9700\u91cd\u5199 12 \u500d\u6570\u636e，\u5199\u653e\u5927\u51ed\u7a7a\u6500\u5347 50%\u3002<\/p>\n<\/li>\n
\u5c0f\u5de5\u4f5c\u96c6\u4e0e\u70ed\u70b9\u8986\u76d6：\u4e1a\u52a1\u901a\u5e38\u53ea\u9ad8\u9891\u66f4\u65b0\u5c40\u90e8\u952e\u7a7a\u95f4\u3002\u82e5\u8fc7\u65e9\u5c06\u70ed\u70b9\u6570\u636e\u538b\u5165\u6df1\u5c42，\u6bcf\u6b21\u6df1\u5c42\u91cd\u5199\u4ee3\u4ef7\u6781\u9ad8\u3002\u82e5\u80fd\u5c06\u5176\u7559\u5728\u6d45\u5c42，\u65b0\u6d8c\u5165\u7684\u5199\u7248\u672c\u4fbf\u80fd\u5728\u6d45\u5c42\u5c31\u5730\u8986\u76d6\u6d88\u9664，\u963b\u6b62\u5199\u653e\u5927\u5411\u6df1\u5c42\u6269\u6563\u3002<\/p>\n<\/li>\n
\u5893\u7891\u6e05\u7406\u7684\u7d27\u8feb\u6027：\u5305\u542b\u5927\u91cf Delete \u5893\u7891\u7684\u6587\u4ef6\u82e5\u4e0d\u5c3d\u65e9\u5f52\u5e76，\u4f1a\u5bf9\u70b9\u67e5\u4e0e\u626b\u63cf\u541e\u5410\u9020\u6210\u6301\u7eed\u62d6\u7d2f\u3002<\/p>\n<\/li>\n
\u57fa\u4e8e\u4ee5\u4e0a\u8003\u91cf，RocksDB \u5728\u00a0include\/rocksdb\/advanced_options.h\u00a0\u4e2d\u5b9a\u4e49\u4e86 5 \u79cd\u5019\u9009\u4f18\u5148\u7ea7：<\/p>\n
C++<\/p>\n
enum CompactionPri : char {
\n kByCompensatedSize = 0x0, \/\/ \u6309\u8865\u507f\u5927\u5c0f\u964d\u5e8f（\u4f18\u5148\u6e05\u7406\u5927\u6587\u4ef6\u6216\u5893\u7891\u591a\u7684\u6587\u4ef6）
\n kOldestLargestSeqFirst = 0x1, \/\/ \u6700\u65e7\u7684\u6700\u5927\u5e8f\u5217\u53f7\u4f18\u5148（\u51b7\u6570\u636e\u4e0b\u6c89，\u70ed\u6570\u636e\u7559\u6d45\u5c42）
\n kOldestSmallestSeqFirst = 0x2, \/\/ \u6700\u65e7\u7684\u6700\u5c0f\u5e8f\u5217\u53f7\u4f18\u5148（\u9632\u9965\u997f，\u5747\u8861\u538b\u5b9e）
\n kMinOverlappingRatio = 0x3, \/\/ \u4e0b\u5c42\u6700\u5c0f\u91cd\u53e0\u6bd4\u4f18\u5148（\u6781\u81f4\u4f18\u5316\u5199\u653e\u5927）
\n kRoundRobin = 0x4, \/\/ \u73b0\u4ee3\u5316\u5927\u8de8\u5ea6\u8f6e\u8f6c
\n};<\/p>\n
| \n kByCompensatedSize<\/p>\n<\/td>\n | \n \u865a\u62df\u8865\u507f\u4f53\u79ef（compensated_file_size）\u964d\u5e8f<\/p>\n<\/td>\n | \n \u4f18\u5148\u56de\u6536\u5927\u6587\u4ef6\u7a7a\u95f4，\u52a0\u901f\u5893\u7891\u6e05\u7406<\/p>\n<\/td>\n | \n \u5ffd\u7565\u76ee\u6807\u5c42\u91cd\u53e0\u5927\u5c0f，\u5199\u653e\u5927\u76f8\u5bf9\u504f\u9ad8<\/p>\n<\/td>\n | \n \u5305\u542b\u5927\u91cf\u6279\u91cf\u5220\u9664（Delete）\u7684\u4e1a\u52a1<\/p>\n<\/td>\n<\/tr>\n |
| \n kOldestLargestSeqFirst<\/p>\n<\/td>\n | \n \u6587\u4ef6\u4e2d\u6700\u5927\u7684\u5e8f\u5217\u53f7（largest_seqno）\u5347\u5e8f<\/p>\n<\/td>\n | \n \u5c06\u51b7\u6570\u636e\u4e0b\u6c89，\u628a\u70ed\u70b9\u7559\u5728\u6d45\u5c42\u5438\u6536\u8986\u76d6\u5199<\/p>\n<\/td>\n | \n \u79bb\u6563\u5199\u5165\u4e0b\u53ef\u80fd\u5bfc\u81f4\u5c40\u90e8\u533a\u95f4\u538b\u5b9e\u4e0d\u5747<\/p>\n<\/td>\n | \n \u5177\u5907\u5178\u578b\u5c0f\u5de5\u4f5c\u96c6\u3001\u5c40\u90e8\u70ed\u70b9\u53cd\u590d\u8986\u76d6\u66f4\u65b0\u7684\u573a\u666f<\/p>\n<\/td>\n<\/tr>\n |
| \n kOldestSmallestSeqFirst<\/p>\n<\/td>\n | \n \u6587\u4ef6\u4e2d\u6700\u5c0f\u7684\u5e8f\u5217\u53f7（smallest_seqno）\u5347\u5e8f<\/p>\n<\/td>\n | \n \u4f18\u5148\u5f52\u5e76\u6700\u4e45\u672a\u66f4\u65b0\u7684\u533a\u95f4，\u9632\u6b62\u5c40\u90e8\u9965\u997f<\/p>\n<\/td>\n | \n \u65e0\u6cd5\u9488\u5bf9\u70ed\u70b9\u6216\u91cd\u53e0\u5ea6\u8fdb\u884c\u52a8\u6001\u4f18\u5316<\/p>\n<\/td>\n | \n \u5168\u952e\u7a7a\u95f4\u5747\u5300\u968f\u673a\u5199\u5165<\/p>\n<\/td>\n<\/tr>\n |
| \n kMinOverlappingRatio<\/p>\n<\/td>\n | \n \u4e0b\u5c42\u91cd\u53e0\u6bd4（$\\\\frac{\\\\text{\u91cd\u53e0\u5b57\u8282}}{\\\\text{\u8865\u507f\u4f53\u79ef}}$）\u5347\u5e8f<\/p>\n<\/td>\n | \n \u6781\u81f4\u964d\u4f4e\u8de8\u5c42\u5199\u653e\u5927，\u6700\u5927\u5316\u96f6\u62f7\u8d1d\u89e6\u53d1\u7387<\/p>\n<\/td>\n | \n \u9047\u5927\u6279\u91cf\u96c6\u4e2d\u5220\u9664\u65f6\u4f1a\u5bfc\u81f4\u5893\u7891\u957f\u671f\u9965\u997f<\/p>\n<\/td>\n | \n \u7eaf\u8ffd\u52a0\u3001\u65f6\u5e8f\u5199\u6216\u5199\u5bc6\u96c6\u578b\u4f4e\u5199\u653e\u5927\u8bc9\u6c42\u573a\u666f<\/p>\n<\/td>\n<\/tr>\n |
| \n kRoundRobin<\/p>\n<\/td>\n | \n \u6e38\u6807\u63a8\u8fdb\u8f6e\u8f6c<\/p>\n<\/td>\n | \n \u952e\u7a7a\u95f4\u5404\u533a\u95f4\u5747\u5300\u63a8\u8fdb，\u907f\u514d\u5c40\u90e8\u5c0f\u788e\u7247\u9891\u7e41\u5f52\u5e76<\/p>\n<\/td>\n | \n \u7f3a\u5c11\u57fa\u4e8e\u91cd\u53e0\u5ea6\u548c\u6570\u636e\u7279\u5f81\u7684\u667a\u80fd\u611f\u77e5<\/p>\n<\/td>\n | \n \u8ffd\u6c42\u541e\u5410\u5e73\u7a33\u3001\u5199\u653e\u5927\u975e\u654f\u611f\u573a\u666f<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n \u6df1\u5165\u5256\u6790 kMinOverlappingRatio \u7684\u6392\u5e8f\u903b\u8f91<\/h5>\n\u5728\u00a0db\/version_set.cc\u00a0\u7684\u00a0SortFileByOverlappingRatio\u00a0\u4e2d，\u6700\u5c0f\u91cd\u53e0\u6bd4\u7b56\u7565\u5c55\u73b0\u4e86\u5177\u4f53\u7684\u6253\u5206\u673a\u5236：<\/p>\n C++<\/p>\n void SortFileByOverlappingRatio(…) { \/\/ \u6838\u5fc3\u8bc4\u5206\u516c\u5f0f：Score \u8d8a\u5c0f，\u4f18\u5148\u7ea7\u8d8a\u9ad8！ \/\/ \u4f9d\u636e\u8bc4\u5206\u505a\u5c40\u90e8\u6392\u5e8f \u5176\u8bc4\u5206\u516c\u5f0f\u4e3a：<\/p>\n $$\\\\text{Score} = \\\\frac{\\\\text{OverlappingBytes} \\\\times 1024}{\\\\text{CompensatedFileSize} \\\\times \\\\text{TTLBoostScore}}$$<\/p>\n
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