add LinkBench README

Author: saffahyjp

README-LinkBench.md

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+# Reproduce LinkBench Results of LiveGraph
+
+As [LinkBench](https://github.com/facebookarchive/linkbench) is implemented in Java and LiveGraph is in C++, we record traces collected from LinkBench Java driver and replay them in a driver of C++ version, so that LiveGraph can perform those queries.
+
+These repositories are used to run LinkBench on LiveGraph:
+
+* A [modified LinkBench Java driver](https://github.com/coolerzxw/LinkBench), with a wrapper implementation which processes the queries correctly (by calling MySQL implementation inside) and also records the operations of each thread into files.
+* A [C++ driver](https://github.com/coolerzxw/LinkBench-Cpp), which reads the queries from files, calls LiveGraph (or other implementations LMDB and RocksDB), and gives performance statistics.
+
+Detailed steps of reproducing are listed as follows. For questions, you may want to open an issue or contact Jiping Yu (yjp19@mails.tsinghua.edu.cn). Also, we are currently working on implementing LinkBench directly in C++, to make reproducing the results easier.
+
+## Recording
+
+Build, config, and run the [modified Java driver](https://github.com/coolerzxw/LinkBench) in the same way as the [original driver](https://github.com/facebookarchive/linkbench). After the run, the recorded traces are written to `record` directory of the current working directory.
+
+## Replaying
+
+Clone and build the C++ driver.
+
+```
+git clone https://github.com/coolerzxw/LinkBench-Cpp.git
+cd LinkBench-Cpp
+mkdir build
+cd build
+cmake ..
+make
+```
+
+You can run each implementation as follows. `[#loaders]` and `[#requesters]` should equal the numbers during recording.
+
+```
+./livegraph [database path] [max #vertices] [trace directory path] [#loaders] [#requesters]
+./lmdb [trace directory path] [#loaders] [#requesters] [database path]
+./rocksdb [trace directory path] [#loaders] [#requesters] [database path]
+```