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XPath: Optimize attribute axis lookup

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When looking for an attribute by name, finding the first attribute means
we can stop looking since attribute names are unique. This makes some
queries faster by 40%.

Another very common pattern in XPath queries is finding an attribute with
a specified value using a predicate (@name = 'value'). While we perform an
optimal amount of traversal in that case, there is a substantial overhead
with evaluating the nodes, saving and restoring the stack state, pushing
the attribute node into a set, etc. Detecting this pattern allows us to
use optimized code, resulting in up to 2x speedup for some queries.

git-svn-id: https://pugixml.googlecode.com/svn/trunk@1061 99668b35-9821-0410-8761-19e4c4f06640
This commit is contained in:
Arseny Kapoulkine 2014-10-16 03:46:42 +00:00
parent 883031fb45
commit 5da51dff27
2 changed files with 60 additions and 15 deletions
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57
src/pugixml.cpp
View File

@ -7473,6 +7473,11 @@ PUGI__NS_BEGIN
*write = 0;
}
inline bool is_xpath_attribute(const char_t* name)
{
return !(starts_with(name, PUGIXML_TEXT("xmlns")) && (name[5] == 0 || name[5] == ':'));
}
struct xpath_variable_boolean: xpath_variable
{
xpath_variable_boolean(): value(false)
@ -8217,7 +8222,6 @@ PUGI__NS_BEGIN
ast_func_normalize_space_0, // normalize-space()
ast_func_normalize_space_1, // normalize-space(left)
ast_func_translate, // translate(left, right, third)
ast_func_translate_table, // translate(left, right, third) where right/third are constants
ast_func_boolean, // boolean(left)
ast_func_not, // not(left)
ast_func_true, // true()
@ -8230,7 +8234,10 @@ PUGI__NS_BEGIN
ast_func_ceiling, // ceiling(left)
ast_func_round, // round(left)
ast_step, // process set left with step
ast_step_root // select root node
ast_step_root, // select root node
ast_opt_translate_table, // translate(left, right, third) where right/third are constants
ast_opt_compare_attribute // @name = 'string'
};
enum axis_t
@ -8296,7 +8303,7 @@ PUGI__NS_BEGIN
xpath_variable* variable;
// node test for ast_step (node name/namespace/node type/pi target)
const char_t* nodetest;
// table for ast_func_translate_table
// table for ast_opt_translate_table
const unsigned char* table;
} _data;
@ -8498,36 +8505,38 @@ PUGI__NS_BEGIN
}
}
void step_push(xpath_node_set_raw& ns, const xml_attribute a, const xml_node parent, xpath_allocator* alloc)
bool step_push(xpath_node_set_raw& ns, const xml_attribute a, const xml_node parent, xpath_allocator* alloc)
{
if (!a) return;
if (!a) return false;
const char_t* name = a.name();
// There are no attribute nodes corresponding to attributes that declare namespaces
// That is, "xmlns:..." or "xmlns"
if (starts_with(name, PUGIXML_TEXT("xmlns")) && (name[5] == 0 || name[5] == ':')) return;
switch (_test)
{
case nodetest_name:
if (strequal(name, _data.nodetest))
if (strequal(name, _data.nodetest) && is_xpath_attribute(name))
{
ns.push_back(xpath_node(a, parent), alloc);
return true;
}
break;
case nodetest_type_node:
case nodetest_all:
ns.push_back(xpath_node(a, parent), alloc);
if (is_xpath_attribute(name))
ns.push_back(xpath_node(a, parent), alloc);
break;
case nodetest_all_in_namespace:
if (starts_with(name, _data.nodetest))
if (starts_with(name, _data.nodetest) && is_xpath_attribute(name))
ns.push_back(xpath_node(a, parent), alloc);
break;
default:
;
}
return false;
}
void step_push(xpath_node_set_raw& ns, const xml_node n, xpath_allocator* alloc)
@ -8589,7 +8598,8 @@ PUGI__NS_BEGIN
case axis_attribute:
{
for (xml_attribute a = n.first_attribute(); a; a = a.next_attribute())
step_push(ns, a, n, alloc);
if (step_push(ns, a, n, alloc))
break; // step_push returns true if it found a unique attribute
break;
}
@ -9007,6 +9017,15 @@ PUGI__NS_BEGIN
return false;
}
case ast_opt_compare_attribute:
{
const char_t* value = (_right->_type == ast_string_constant) ? _right->_data.string : _right->_data.variable->get_string();
xml_attribute attr = c.n.node().attribute(_left->_data.nodetest);
return attr && strequal(attr.value(), value) && is_xpath_attribute(attr.name());
}
case ast_variable:
{
assert(_rettype == _data.variable->type());
@ -9412,7 +9431,7 @@ PUGI__NS_BEGIN
return s;
}
case ast_func_translate_table:
case ast_opt_translate_table:
{
xpath_string s = _left->eval_string(c, stack);
@ -9610,10 +9629,18 @@ PUGI__NS_BEGIN
if (table)
{
_type = ast_func_translate_table;
_type = ast_opt_translate_table;
_data.table = table;
}
}
// Use optimized path for @attr = 'value' or @attr = $value
if (_type == ast_op_equal &&
_left->_type == ast_step && _left->_axis == axis_attribute && _left->_test == nodetest_name && !_left->_left && !_left->_right &&
(_right->_type == ast_string_constant || (_right->_type == ast_variable && _right->rettype() == xpath_type_string)))
{
_type = ast_opt_compare_attribute;
}
}
bool is_posinv_expr() const

18
tests/test_xpath_paths.cpp
View File

@ -561,4 +561,22 @@ TEST_XML(xpath_paths_unsorted_child, "<node><foo><bar/></foo><node><foo><bar/></
CHECK(ns[2] == nss[1]);
}
TEST_XML(xpath_paths_optimize_compare_attribute, "<node id='1' /><node id='2' /><node xmlns='3' />")
{
CHECK_XPATH_NODESET(doc, STR("node[@id = '1']")) % 2;
CHECK_XPATH_NODESET(doc, STR("node[@id = '2']")) % 4;
CHECK_XPATH_NODESET(doc, STR("node[@id = 2]")) % 4;
CHECK_XPATH_NODESET(doc, STR("node[@id[. > 3] = '2']"));
CHECK_XPATH_NODESET(doc, STR("node['1' = @id]")) % 2;
xpath_variable_set set;
set.set(STR("var1"), STR("2"));
set.set(STR("var2"), 2.0);
CHECK_XPATH_NODESET_VAR(doc, STR("node[@id = $var1]"), &set) % 4;
CHECK_XPATH_NODESET_VAR(doc, STR("node[@id = $var2]"), &set) % 4;
CHECK_XPATH_NODESET(doc, STR("node[@xmlns = '3']"));
}
#endif