SipHash: allowed not to call update for empty strings (less than 0.3% performance degradation on all test data) [#METR-16781].

dbms/include/DB/Common/SipHash.h

@@ -76,6 +76,7 @@ public:
 		v3 = 0x7465646279746573ULL ^ k1;
 
 		cnt = 0;
+		current_word = 0;
 	}
 
 	void update(const char * data, u64 size)

dbms/src/Common/tests/sip_hash_perf.cpp

@@ -0,0 +1,71 @@
+#include <vector>
+#include <string>
+#include <iomanip>
+
+#include <DB/Common/SipHash.h>
+#include <DB/IO/ReadBufferFromFileDescriptor.h>
+#include <DB/IO/ReadHelpers.h>
+#include <statdaemons/Stopwatch.h>
+
+
+/** Тестировать так:
+  *
+  * clickhouse-client --query="SELECT SearchPhrase AS k FROM test.hits WHERE k != ''" > phrases.tsv
+  * clickhouse-client --query="SELECT URL AS k FROM test.hits" > urls.tsv
+  * clickhouse-client --query="SELECT SearchPhrase AS k FROM test.hits" > phrases_with_empty.tsv
+  * clickhouse-client --query="SELECT Title AS k FROM test.hits" > titles.tsv
+  * clickhouse-client --query="SELECT PageCharset AS k FROM test.hits" > charset.tsv
+  *
+  * for i in {1..1000}; do ./sip_hash_perf < titles.tsv 2>&1 | grep Processed | grep -oP '\d+\.\d+ rows/sec'; done | awk '{ if ($1 > x) { x = $1; print x } }'
+  */
+
+
+int main(int argc, char ** argv)
+{
+	std::vector<std::string> data;
+	DB::ReadBufferFromFileDescriptor in(STDIN_FILENO);
+
+	std::cerr << std::fixed << std::setprecision(3);
+
+	{
+		Stopwatch watch;
+
+		while (!in.eof())
+		{
+			data.emplace_back();
+			DB::readEscapedString(data.back(), in);
+			DB::assertString("\n", in);
+		}
+
+		double seconds = watch.elapsedSeconds();
+		std::cerr << "Read "
+			<< data.size() << " rows, "
+			<< (in.count() / 1048576.0) << " MiB "
+			<< " in " << seconds << " sec., "
+			<< (data.size() / seconds) << " rows/sec., "
+			<< (in.count() / 1048576.0 / seconds) << " MiB/sec.\n";
+	}
+
+	{
+		size_t res = 0;
+		Stopwatch watch;
+
+		for (const auto & s : data)
+		{
+			SipHash hash;
+			hash.update(s.data(), s.size());
+			res += hash.get64();
+		}
+
+		double seconds = watch.elapsedSeconds();
+		std::cerr << "Processed "
+			<< data.size() << " rows, "
+			<< (in.count() / 1048576.0) << " MiB "
+			<< " in " << seconds << " sec., "
+			<< (data.size() / seconds) << " rows/sec., "
+			<< (in.count() / 1048576.0 / seconds) << " MiB/sec. "
+			<< "(res = " << res << ")\n";
+	}
+
+	return 0;
+}