Don't crash if group by attrib is empty string.

bin/pt-query-digest

@@ -5453,7 +5453,7 @@ sub _calc_metrics {
 sub metrics {
    my ( $self, %args ) = @_;
    foreach my $arg ( qw(attrib where) ) {
-      die "I need a $arg argument" unless $args{$arg};
+      die "I need a $arg argument" unless defined $args{$arg};
    }
    my $attrib = $args{attrib};
    my $where   = $args{where};
@@ -6365,7 +6365,7 @@ sub files {
 sub header {
    my ( $self, %args ) = @_;
    foreach my $arg ( qw(ea orderby) ) {
-      die "I need a $arg argument" unless $args{$arg};
+      die "I need a $arg argument" unless defined $args{$arg};
    }
    my $ea      = $args{ea};
    my $orderby = $args{orderby};
@@ -6594,7 +6594,7 @@ sub query_report {
 sub event_report {
    my ( $self, %args ) = @_;
    foreach my $arg ( qw(ea item orderby) ) {
-      die "I need a $arg argument" unless $args{$arg};
+      die "I need a $arg argument" unless defined $args{$arg};
    }
    my $ea      = $args{ea};
    my $item    = $args{item};
@@ -6765,7 +6765,7 @@ sub event_report {
 sub chart_distro {
    my ( $self, %args ) = @_;
    foreach my $arg ( qw(ea item attrib) ) {
-      die "I need a $arg argument" unless $args{$arg};
+      die "I need a $arg argument" unless defined $args{$arg};
    }
    my $ea     = $args{ea};
    my $item   = $args{item};
@@ -6814,7 +6814,7 @@ sub chart_distro {
 sub distro_sparkline {
    my ( $self, %args ) = @_;
    foreach my $arg ( qw(ea item attrib) ) {
-      die "I need a $arg argument" unless $args{$arg};
+      die "I need a $arg argument" unless defined $args{$arg};
    }
    my $ea     = $args{ea};
    my $item   = $args{item};

lib/EventAggregator.pm

@@ -764,7 +764,7 @@ sub _calc_metrics {
 sub metrics {
    my ( $self, %args ) = @_;
    foreach my $arg ( qw(attrib where) ) {
-      die "I need a $arg argument" unless $args{$arg};
+      die "I need a $arg argument" unless defined $args{$arg};
    }
    my $attrib = $args{attrib};
    my $where   = $args{where};

lib/QueryReportFormatter.pm

@@ -209,7 +209,7 @@ sub files {
 sub header {
    my ( $self, %args ) = @_;
    foreach my $arg ( qw(ea orderby) ) {
-      die "I need a $arg argument" unless $args{$arg};
+      die "I need a $arg argument" unless defined $args{$arg};
    }
    my $ea      = $args{ea};
    my $orderby = $args{orderby};
@@ -489,7 +489,7 @@ sub query_report {
 sub event_report {
    my ( $self, %args ) = @_;
    foreach my $arg ( qw(ea item orderby) ) {
-      die "I need a $arg argument" unless $args{$arg};
+      die "I need a $arg argument" unless defined $args{$arg};
    }
    my $ea      = $args{ea};
    my $item    = $args{item};
@@ -686,7 +686,7 @@ sub event_report {
 sub chart_distro {
    my ( $self, %args ) = @_;
    foreach my $arg ( qw(ea item attrib) ) {
-      die "I need a $arg argument" unless $args{$arg};
+      die "I need a $arg argument" unless defined $args{$arg};
    }
    my $ea     = $args{ea};
    my $item   = $args{item};
@@ -765,7 +765,7 @@ sub chart_distro {
 sub distro_sparkline {
    my ( $self, %args ) = @_;
    foreach my $arg ( qw(ea item attrib) ) {
-      die "I need a $arg argument" unless $args{$arg};
+      die "I need a $arg argument" unless defined $args{$arg};
    }
    my $ea     = $args{ea};
    my $item   = $args{item};

t/lib/EventAggregator.t

@@ -9,7 +9,7 @@ BEGIN {
 use strict;
 use warnings FATAL => 'all';
 use English qw(-no_match_vars);
-use Test::More tests => 81;
+use Test::More tests => 82;
 
 use QueryRewriter;
 use EventAggregator;
@@ -1924,6 +1924,21 @@ is(
    "Parse InnoDB_trx_id as string"
 );
 
+# #############################################################################
+# Bug 924950: pt-query-digest --group-by db may crash profile report
+# #############################################################################
+$ea = new EventAggregator(
+   groupby => 'Schema',
+   worst   => 'Query_time',
+);
+parse_file('t/lib/samples/slowlogs/slow055.txt', $p, $ea);
+my $m = $ea->metrics(where => '', attrib => 'Query_time');
+is(
+   $m->{cnt},
+   3,
+   "Metrics for '' attrib (bug 924950)"
+);
+
 # #############################################################################
 # Done.
 # #############################################################################

t/lib/samples/slowlogs/slow055.txt

@@ -0,0 +1,15 @@
+# User@Host: meow[meow] @  [1.2.3.8]
+# Thread_id: 5  Schema: 
+# Query_time: 0.000002  Lock_time: 0.000000  Rows_sent: 0  Rows_examined: 0
+# No InnoDB statistics available for this query
+# administrator command: Quit;
+# User@Host: meow[meow] @  [1.2.3.8]
+# Thread_id: 6  Schema: 
+# Query_time: 0.000899  Lock_time: 0.000000  Rows_sent: 0  Rows_examined: 0
+# No InnoDB statistics available for this query
+SET NAMES utf8;
+# User@Host: meow[meow] @  [1.2.3.8]
+# Thread_id: 6  Schema: 
+# Query_time: 0.018799  Lock_time: 0.009453  Rows_sent: 0  Rows_examined: 0
+# No InnoDB statistics available for this query
+SELECT MIN(id),MAX(id) FROM tbl;

t/pt-query-digest/samples/slow055.txt

@@ -0,0 +1,30 @@
+
+# ########################################################################
+# Report grouped by db
+# ########################################################################
+
+# Item 1: 0 QPS, 0x concurrency, ID 0xE9800998ECF8427E at byte 420 _______
+# This item is included in the report because it matches --limit.
+# Scores: Apdex = 1.00 [1.0]*, V/M = 0.01
+# Query_time sparkline: |^ ^ ^   |
+# Attribute    pct   total     min     max     avg     95%  stddev  median
+# ============ === ======= ======= ======= ======= ======= ======= =======
+# Count        100       3
+# Exec time    100    20ms     2us    19ms     7ms    18ms     8ms   881us
+# Lock time    100     9ms       0     9ms     3ms     9ms     4ms       0
+# Rows sent      0       0       0       0       0       0       0       0
+# Rows examine   0       0       0       0       0       0       0       0
+# Query size   100      72      14      31      24   30.19    6.95   26.08
+# String:
+# Hosts
+# Users        meow
+# Query_time distribution
+#   1us  ################################################################
+#  10us
+# 100us  ################################################################
+#   1ms
+#  10ms  ################################################################
+# 100ms
+#    1s
+#  10s+
+

t/pt-query-digest/slowlog_analyses.t

@@ -9,7 +9,7 @@ BEGIN {
 use strict;
 use warnings FATAL => 'all';
 use English qw(-no_match_vars);
-use Test::More tests => 43;
+use Test::More tests => 44;
 
 use PerconaTest;
 
@@ -433,6 +433,18 @@ ok(
    'Analysis for slow054 (InnoDB_trx_id bug 821694)'
 );
 
+# #############################################################################
+# Bug 924950: pt-query-digest --group-by db may crash profile report
+# #############################################################################
+ok(
+   no_diff(
+      sub { pt_query_digest::main(@args, $sample.'slow055.txt',
+         qw(--group-by db)) },
+      "t/pt-query-digest/samples/slow055.txt",
+   ),
+   'Analysis for slow055 (group by blank db bug 924950)'
+);
+
 # #############################################################################
 # Done.
 # #############################################################################