diff --git a/.gitignore b/.gitignore
index 1cea8c20f..8bba1b851 100644
--- a/.gitignore
+++ b/.gitignore
@@ -50,3 +50,5 @@ java/**.asc
 java/javadoc
 
 scan_build_report/
+t
+LOG
diff --git a/Makefile b/Makefile
index c2fb434e6..efb97fa6d 100644
--- a/Makefile
+++ b/Makefile
@@ -6,12 +6,21 @@
 
 #-----------------------------------------------
 
+CLEAN_FILES = # deliberately empty, so we can append below.
 CFLAGS += ${EXTRA_CFLAGS}
 CXXFLAGS += ${EXTRA_CXXFLAGS}
 LDFLAGS += $(EXTRA_LDFLAGS)
 MACHINE ?= $(shell uname -m)
 ARFLAGS = rs
 
+# Transform parallel LOG output into something more readable.
+perl_command = perl -n \
+  -e '@a=split("\t",$$_,-1); $$t=$$a[8]; $$t =~ s,^\./,,;'		\
+  -e '$$t =~ s, >.*,,; chomp $$t;'					\
+  -e '$$t =~ /.*--gtest_filter=(.*?\.[\w\/]+)/ and $$t=$$1;'		\
+  -e 'printf "%7.3f %s %s\n", $$a[3], $$a[6] == 0 ? "PASS" : "FAIL", $$t'
+quoted_perl_command = $(subst ','\'',$(perl_command))
+
 ifneq ($(MAKECMDGOALS),dbg)
 OPT += -O2 -fno-omit-frame-pointer
 ifneq ($(MACHINE),ppc64) # ppc64 doesn't support -momit-leaf-frame-pointer
@@ -64,6 +73,7 @@ AM_LINK = $(AM_V_CCLD)$(CXX) $^ $(EXEC_LDFLAGS) -o $@ $(LDFLAGS) $(COVERAGEFLAGS
 dummy := $(shell (export ROCKSDB_ROOT="$(CURDIR)"; "$(CURDIR)/build_tools/build_detect_platform" "$(CURDIR)/make_config.mk"))
 # this file is generated by the previous line to set build flags and sources
 include make_config.mk
+CLEAN_FILES += make_config.mk
 
 ifneq ($(PLATFORM), IOS)
 CFLAGS += -g
@@ -163,6 +173,7 @@ gen_build_version =							\
 # as a regular source file as part of the compilation process.
 # One can run "strings executable_filename | grep _build_" to find
 # the version of the source that we used to build the executable file.
+CLEAN_FILES += util/build_version.cc:
 FORCE:
 util/build_version.cc: FORCE
 	$(AM_V_GEN)rm -f $@-t
@@ -332,18 +343,149 @@ release:
 coverage:
 	$(MAKE) clean
 	COVERAGEFLAGS="-fprofile-arcs -ftest-coverage" LDFLAGS+="-lgcov" $(MAKE) all check -j32
-	(cd coverage; ./coverage_test.sh)
-	# Delete intermediate files
+	cd coverage && ./coverage_test.sh
+        # Delete intermediate files
 	find . -type f -regex ".*\.\(\(gcda\)\|\(gcno\)\)" -exec rm {} \;
 
-check: all
-	for t in $(TESTS); do echo "***** Running $$t"; ./$$t || exit 1; done
-	python tools/ldb_test.py
+# Extract the names of its tests by running db_test with --gtest_list_tests.
+# This filter removes the "#"-introduced comments, and expands to
+# fully-qualified names by changing input like this:
+#
+#   DBTest.
+#     Empty
+#     WriteEmptyBatch
+#   MultiThreaded/MultiThreadedDBTest.
+#     MultiThreaded/0  # GetParam() = 0
+#     MultiThreaded/1  # GetParam() = 1
+#
+# into this:
+#
+#   DBTest.Empty
+#   DBTest.WriteEmptyBatch
+#   MultiThreaded/MultiThreadedDBTest.MultiThreaded/0
+#   MultiThreaded/MultiThreadedDBTest.MultiThreaded/1
+#
+test_names = \
+  ./db_test --gtest_list_tests						\
+    | perl -n								\
+      -e 's/ *\#.*//;'							\
+      -e '/^(\s*)(\S+)/; !$$1 and do {$$p=$$2; break};'			\
+      -e 'print qq! $$p$$2!'
+
+ifeq ($(MAKECMDGOALS),check)
+# Use /dev/shm if it has the sticky bit set (otherwise, /tmp),
+# and create a randomly-named rocksdb.XXXX directory therein.
+# We'll use that directory in the "make check" rules.
+ifeq ($(TMPD),)
+TMPD := $(shell f=/dev/shm; test -k $$f || f=/tmp;			\
+  perl -le 'use File::Temp "tempdir";'					\
+    -e 'print tempdir("'$$f'/rocksdb.XXXX", CLEANUP => 0)')
+endif
+endif
 
-check_some: $(SUBSET) ldb
-	for t in $(SUBSET); do echo "***** Running $$t"; ./$$t || exit 1; done
-	python tools/ldb_test.py
+ifneq ($(T),)
+
+# Run all tests in parallel, accumulating per-test logs in t/log-*.
+
+# t_sanitized is each $(T) with "-" in place of each "/".
+t_sanitized = $(subst /,-,$(T))
+
+# t_run is each sanitized name with a leading "t/".
+t_run = $(patsubst %,t/%,$(t_sanitized))
+
+# Each t_run file is a tiny generated bourne shell script
+# that invokes one of db_tests's sub-tests. Why use a file
+# for this?  Because that makes the invocation of parallel
+# below simpler, which in turn makes the parsing of parallel's
+# LOG simpler (the latter is for live monitoring as parallel
+# tests run).
+filter = --gtest_filter=$(subst -,/,$(@F))
+$(t_run): Makefile db_test
+	$(AM_V_GEN)mkdir -p t
+	$(AM_V_at)rm -f $@ $@-t
+	$(AM_V_at)printf '%s\n'						\
+	    '#!/bin/sh'							\
+	    'd=$(TMPD)/$(@F)'						\
+	    'mkdir -p $$d'						\
+	    'TEST_TMPDIR=$$d ./db_test $(filter)'			\
+	  > $@-t
+	$(AM_V_at)chmod a=rx $@-t
+	$(AM_V_at)mv $@-t $@
+
+# Reorder input lines (which are one per test) so that the
+# longest-running tests appear first in the output.
+# Do this by prefixing each selected name with its duration,
+# sort the resulting names, and remove the leading numbers.
+# FIXME: the "100" we prepend is a fake time, for now.
+# FIXME: squirrel away timings from each run and use them
+# (when present) on subsequent runs to order these tests.
+#
+# Without this reordering, these two tests would happen to start only
+# after almost all other tests had completed, thus adding 100 seconds
+# to the duration of parallel "make check".  That's the difference
+# between 4 minutes (old) and 2m20s (new).
+#
+# 152.120 PASS t/DBTest.FileCreationRandomFailure
+# 107.816 PASS t/DBTest.EncodeDecompressedBlockSizeTest
+#
+slow_test_regexp = \
+  ^t/DBTest\.(?:FileCreationRandomFailure|EncodeDecompressedBlockSizeTest)$$
+prioritize_long_running_tests =						\
+  perl -pe 's,($(slow_test_regexp)),100 $$1,'				\
+    | sort -k1,1gr							\
+    | sed 's/^[.0-9]* //'
+
+# "make check" uses
+# Run with "make J=1 check" to disable parallelism in "make check".
+# Run with "make J=200% check" to run two parallel jobs per core.
+# The default is to run one job per core (J=100%).
+# See "man parallel" for its "-j ..." option.
+J = 100%
+
+.PHONY: check_0
+check_0: $(t_run)
+	$(AM_V_GEN)export TEST_TMPDIR=$(TMPD);				\
+	printf '%s\n' ''						\
+	  'To monitor subtest <duration,pass/fail,name>,'		\
+	  '  run "make watch-log" in a separate window' '';		\
+	test -t 1 && eta=--eta || eta=;					\
+	{								\
+	  printf './%s\n' $(filter-out db_test, $(TESTS));		\
+	  printf '%s\n' $(t_run);					\
+	}								\
+	  | $(prioritize_long_running_tests)				\
+	  | parallel -j$(J) --joblog=LOG $$eta --gnu '{} >& t/log-{/}'
+endif
+
+CLEAN_FILES += t LOG $(TMPD)
 
+# When running parallel "make check", you can monitor its progress
+# from another window.
+# Run "make watch_LOG" to show the duration,PASS/FAIL,name of parallel
+# tests as they are being run.  We sort them so that longer-running ones
+# appear at the top of the list and any failing tests remain at the top
+# regardless of their duration. As with any use of "watch", hit ^C to
+# interrupt.
+watch-log:
+	watch --interval=0 'sort -k7,7nr -k4,4gr LOG|$(quoted_perl_command)'
+
+# If GNU parallel is installed, run the tests in parallel,
+# via the check_0 rule above.  Otherwise, run them sequentially.
+check: all
+	$(AM_V_GEN)case $$(parallel --gnu --help 2>/dev/null) in	\
+	  *'GNU Parallel'*)						\
+	    t=$$($(test_names));					\
+	    $(MAKE) T="$$t" TMPD=$(TMPD) check_0;;			\
+	  *)								\
+	    for t in $(TESTS); do					\
+	      echo "===== Running $$t"; ./$$t || exit 1; done;;		\
+	esac
+	rm -rf $(TMPD)
+
+check_some: $(SUBSET) ldb_tests
+	for t in $(SUBSET); do echo "===== Running $$t"; ./$$t || exit 1; done
+
+.PHONY: ldb_tests
 ldb_tests: ldb
 	python tools/ldb_test.py
 
@@ -385,7 +527,8 @@ analyze: clean
 		-o $(CURDIR)/scan_build_report \
 		$(MAKE) dbg
 
-unity.cc:
+CLEAN_FILES += unity.cc
+unity.cc: Makefile
 	rm -f $@ $@-t
 	for source_file in $(LIB_SOURCES); do \
 		echo "#include <$$source_file>" >> $@-t; \
@@ -398,9 +541,8 @@ unity: unity.o
 	$(AM_LINK)
 
 clean:
-	rm -f $(BENCHMARKS) $(TOOLS) $(TESTS) $(LIBRARY) $(SHARED) make_config.mk unity.cc
-	rm -f util/build_version.cc
-	rm -rf ios-x86 ios-arm scan_build_report
+	rm -f $(BENCHMARKS) $(TOOLS) $(TESTS) $(LIBRARY) $(SHARED)
+	rm -rf $(CLEAN_FILES) ios-x86 ios-arm scan_build_report
 	find . -name "*.[oda]" -exec rm {} \;
 	find . -type f -regex ".*\.\(\(gcda\)\|\(gcno\)\)" -exec rm {} \;
 	rm -rf bzip2* snappy* zlib* lz4*
@@ -811,18 +953,18 @@ endif
 #  	Source files dependencies detection
 # ---------------------------------------------------------------------------
 
+all_sources = $(LIB_SOURCES) $(TEST_BENCH_SOURCES) $(MOCK_SOURCES)
+DEPFILES = $(all_sources:.cc=.d)
+
 # Add proper dependency support so changing a .h file forces a .cc file to
 # rebuild.
 
 # The .d file indicates .cc file's dependencies on .h files. We generate such
 # dependency by g++'s -MM option, whose output is a make dependency rule.
-%.d: %.cc
+$(DEPFILES): %.d: %.cc
 	@$(CXX) $(CXXFLAGS) $(PLATFORM_SHARED_CFLAGS) \
 	  -MM -MT'$@' -MT'$(<:.cc=.o)' "$<" -o '$@'
 
-all_sources = $(LIB_SOURCES) $(TEST_BENCH_SOURCES) $(MOCK_SOURCES)
-DEPFILES = $(all_sources:.cc=.d)
-
 depend: $(DEPFILES)
 
 # if the make goal is either "clean" or "format", we shouldn't