parallel: With many --sqlworkers minimize the number of duplicates.

NEWS

@@ -1,3 +1,5 @@
+
+
 20200522
 
 New in this release:

doc/release_new_version

@@ -188,7 +188,7 @@ from:tange@gnu.org
 to:parallel@gnu.org, bug-parallel@gnu.org
 stable-bcc: Jesse Alama <jessealama@fastmail.fm>
 
-Subject: GNU Parallel 20200622 ('SpaceX') released <<[stable]>>
+Subject: GNU Parallel 20200622 ('SpaceX/Floyd') released <<[stable]>>
 
 GNU Parallel 20200622 ('') <<[stable]>> has been released. It is available for download at: http://ftpmirror.gnu.org/parallel/
 
@@ -201,12 +201,18 @@ Quote of the month:
 New in this release:
 
 *
+https://www.slideshare.net/hoffmanlab/gnu-parallel-194030490
+https://www.openskysoftware.com/site-credits.htm
 
 
 * Bug fixes and man page updates.
 
 News about GNU Parallel:
 
+https://bioinformaticsworkbook.org/Appendix/GNUparallel/GNU_parallel_examples.html#gsc.tab=0
+
+http://pdebuyl.be/blog/2020/gnu-parallel-for-simulations.html
+
 https://negfeedback.blogspot.com/2020/05/indispensable-command-line-tools.html
 
 Get the book: GNU Parallel 2018 http://www.lulu.com/shop/ole-tange/gnu-parallel-2018/paperback/product-23558902.html

src/parallel

@@ -12299,8 +12299,13 @@ sub new($) {
     my $dbh;
     if($driver eq "CSV") {
 	# CSV does not use normal dsn
+	if(-d $database) {
 	    $dbh = DBI->connect("dbi:CSV:", "", "", { f_dir => "$database", })
 		or die $DBI::errstr;
+	} else {
+	    ::error("$database is not a directory.");
+	    ::wait_and_exit(255);
+	}
     } else {
 	$dbh = DBI->connect($dsn, $userid, $password,
 			   { RaiseError => 1, AutoInactiveDestroy => 1 })
@@ -12311,7 +12316,6 @@ sub new($) {
     $dbh->{'RaiseError'} = 1;
     $dbh->{'ShowErrorStatement'} = 1;
     $dbh->{'HandleError'} = sub {};
-
     if(not defined $options{'table'}) {
 	::error("The DBURL ($dburl) must contain a table.");
 	::wait_and_exit(255);
@@ -12650,13 +12654,37 @@ sub insert_records($) {
 	       0, @$record_ref[1..$#$record_ref]);
 }
 
+
 sub get_record($) {
     my $self = shift;
     my @retval;
     my $table = $self->table();
     my @v_cols = map { ", V$_" } (1..$self->max_number_of_args());
-    my $v = $self->get("SELECT Seq, Command @v_cols FROM $table ".
-		       "WHERE Exitval = -1000 ORDER BY Seq LIMIT 1;");
+    my $rand = "Reserved-".$$.rand();
+    my $v;
+    my $more_pending;
+
+    do {
+	if($self->{'driver'} eq "CSV") {
+	    # Sub SELECT is not supported in CSV
+	    # So to minimize the race condition below select a job at random
+	    my $r = $self->get("SELECT Seq, Command @v_cols FROM $table ".
+			       "WHERE Exitval = -1000 LIMIT 100;");
+	    $v = [ sort { rand() > 0.5 } @$r ];
+	} else {
+	    # Avoid race condition where multiple workers get the same job
+	    # by setting Stdout to a unique string
+	    # (SELECT * FROM (...) AS dummy) is needed due to sillyness in MySQL
+	    $self->update("SET Stdout = ?,Exitval = ? ".
+			  "WHERE Seq = (".
+			  "  SELECT * FROM (".
+			  "    SELECT min(Seq) FROM $table WHERE Exitval = -1000".
+			  "  ) AS dummy".
+			  ") AND Exitval = -1000;", $rand, -1210);
+	    # If a parallel worker overwrote the unique string this will get nothing
+	    $v = $self->get("SELECT Seq, Command @v_cols FROM $table ".
+			    "WHERE Stdout = ?;", $rand);
+	}
 	if($v->[0]) {
 	    my $val_ref = $v->[0];
 	    # Mark record as taken
@@ -12664,12 +12692,20 @@ sub get_record($) {
 	    # Save the sequence number to use when running the job
 	    $SQL::next_seq = $seq;
 	    $self->update("SET Exitval = ? WHERE Seq = ".$seq, -1220);
+	    # Command is encoded with '\257 space' as splitting char
 	    my @command = split /\257 /, shift @$val_ref;
 	    $SQL::command_ref = \@command;
 	    for (@$val_ref) {
 		push @retval, Arg->new($_);
 	    }
+	} else {
+	    # If the record was updated by another job in parallel,
+	    # then we may not be done, so see if there are more jobs pending
+	    $more_pending =
+		$self->get("SELECT Seq FROM $table WHERE Exitval = ?;", -1210);
 	}
+    } while (not $v->[0] and $more_pending->[0]);
+
     if(@retval) {
 	return \@retval;
     } else {

src/parallel.pod

@@ -2380,8 +2380,11 @@ E.g.
   sql:oracle://scott:tiger@ora.example.com/xe/parjob
   postgresql://scott:tiger@pg.example.com/pgdb/parjob
   pg:///parjob
-  sqlite3:///pardb/parjob.sqlite
-  csv:///%2Ftmp%2Fmydir/jobtable
+  sqlite3:///%2Ftmp%2Fpardb.sqlite/parjob
+  csv:///%2Ftmp%2Fpardb/parjob
+
+Notice how / in the path of sqlite and CVS must be encoded as
+%2F. Except the last / in CSV which must be a /.
 
 It can also be an alias from ~/.sql/aliases:
 

testsuite/tests-to-run/parallel-local-sql01.sh

@@ -6,9 +6,11 @@
 export SQLITE=sqlite3:///%2Frun%2Fshm%2Fparallel.db
 export PG=pg://`whoami`:`whoami`@lo/`whoami`
 export MYSQL=mysql://`whoami`:`whoami`@lo/`whoami`
+export CSV=csv:///%2Frun%2Fshm%2Fcsv
 
 export DEBUG=false
-rm /run/shm/parallel.db
+rm -f /run/shm/parallel.db
+mkdir -p /run/shm/csv
 
 p_showsqlresult() {
   SERVERURL=$1
@@ -125,7 +127,8 @@ export -f $(compgen -A function | egrep 'p_|par_')
 # Tested that -j0 in parallel is fastest (up to 15 jobs)
 compgen -A function | grep par_ | sort |
   stdout parallel -vj5 -k --tag --joblog /tmp/jl-`basename $0` p_wrapper \
-	 :::: - ::: \$MYSQL \$PG \$SQLITE | perl -pe 's/tbl\d+/TBL99999/gi;' |
+	 :::: - ::: \$MYSQL \$PG \$SQLITE \$CSV |
+  perl -pe 's/tbl\d+/TBL99999/gi;' |
   perl -pe 's/(from TBL99999 order) .*/$1/g' |
   perl -pe 's/ *\b'"$hostname"'\b */hostname/g' | 
   grep -v -- --------------- |

testsuite/tests-to-run/parallel-local-sql02.sh

@@ -0,0 +1,45 @@
+#!/bin/bash
+
+# GNU Parallel SQL tests
+# The tests must be able to run in parallel
+
+export SQLITE=sqlite3:///%2Frun%2Fshm%2Fparallel.db
+export PG=pg://`whoami`:`whoami`@lo/`whoami`
+export MYSQL=mysql://`whoami`:`whoami`@lo/`whoami`
+export CSV=csv:///%2Frun%2Fshm%2Fcsv
+
+rm -f /run/shm/parallel.db
+mkdir -p /run/shm/csv
+
+par_few_duplicate_run() {
+    echo '### With many workers there will be some duplicates'
+    TABLE=TBL$RANDOM
+    DBURL="$1"/$TABLE
+    parallel --sqlmaster $DBURL echo ::: {1..100}
+    lines=$( (
+	       parallel --sqlworker $DBURL &
+	       parallel --sqlworker $DBURL &
+	       parallel --sqlworker $DBURL &
+	       parallel --sqlworker $DBURL &
+	       wait
+	   ) | wc -l)
+    if [ $lines -gt 105 ] ; then
+	echo Error: $lines are more than 5% duplicates
+    else
+	echo OK
+    fi
+}
+
+hostname=`hostname`
+export -f $(compgen -A function | egrep 'p_|par_')
+# Tested that -j0 in parallel is fastest (up to 15 jobs)
+compgen -A function | grep par_ | sort |
+  stdout parallel -vj5 -k --tag --joblog /tmp/jl-`basename $0` {1} {2} \
+	 :::: - :::  \$CSV \$MYSQL \$PG \$SQLITE |
+  perl -pe 's/tbl\d+/TBL99999/gi;' |
+  perl -pe 's/(from TBL99999 order) .*/$1/g' |
+  perl -pe 's/ *\b'"$hostname"'\b */hostname/g' | 
+  grep -v -- --------------- |
+  perl -pe 's/ *\bhost\b */host/g' |
+  perl -pe 's/ +/ /g'
+

testsuite/wanted-results/parallel-local-sql02

@@ -0,0 +1,12 @@
+par_few_duplicate_run $CSV	par_few_duplicate_run $CSV
+par_few_duplicate_run $CSV	### With many workers there will be some duplicates
+par_few_duplicate_run $CSV	OK
+par_few_duplicate_run $MYSQL	par_few_duplicate_run $MYSQL
+par_few_duplicate_run $MYSQL	### With many workers there will be some duplicates
+par_few_duplicate_run $MYSQL	OK
+par_few_duplicate_run $PG	par_few_duplicate_run $PG
+par_few_duplicate_run $PG	### With many workers there will be some duplicates
+par_few_duplicate_run $PG	OK
+par_few_duplicate_run $SQLITE	par_few_duplicate_run $SQLITE
+par_few_duplicate_run $SQLITE	### With many workers there will be some duplicates
+par_few_duplicate_run $SQLITE	OK