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[Memcached_DataObject] Change how multiGet achieves an ordered result 

The previous approach sent the key values twice, which for large sets is
twice as bad.

As an optional feature of this approach multiGet now allows retrieving tuples
in exact order and amount of the requested key values.
This commit is contained in:
Alexei Sorokin 2020-09-03 18:11:12 +03:00
parent 55136c1c6f
commit 4884a97223
2 changed files with 132 additions and 78 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
classes/Managed_DataObject.php
View File

@ -75,15 +75,25 @@ abstract class Managed_DataObject extends Memcached_DataObject
/**
* Get multiple items from the database by key
*
* @param string $keyCol name of column for key
* @param array $keyVals key values to fetch
* @param boolean $skipNulls return only non-null results?
*
* @return array Array of objects, in order
* @param string $keyCol name of column for key
* @param array $keyVals key values to fetch
* @param bool $skipNulls return only non-null results
* @param bool $preserve return the same tuples as input
* @return object An object with tuples to be fetched, in order
*/
public static function multiGet($keyCol, array $keyVals, $skipNulls = true)
{
return parent::multiGetClass(get_called_class(), $keyCol, $keyVals, $skipNulls);
public static function multiGet(
string $keyCol,
array $keyVals,
bool $skipNulls = true,
bool $preserve = false
): object {
return parent::multiGetClass(
get_called_class(),
$keyCol,
$keyVals,
$skipNulls,
$preserve
);
}
/**
@ -312,11 +322,6 @@ abstract class Managed_DataObject extends Memcached_DataObject
return $ckeys;
}
public function escapedTableName()
{
return common_database_tablename($this->tableName());
}
/**
* Returns an object by looking at the primary key column(s).
*

179
classes/Memcached_DataObject.php
View File

@ -66,87 +66,131 @@ class Memcached_DataObject extends Safe_DataObject
/**
* Get multiple items from the database by key
*
* @param string $cls Class to fetch
* @param string $keyCol name of column for key
* @param array $keyVals key values to fetch
* @param boolean $skipNulls skip provided null values
*
* @return array Array of objects, in order
* @param string $cls Class to fetch
* @param string $keyCol name of column for key
* @param array $keyVals key values to fetch
* @param bool $skipNulls return only non-null results
* @param bool $preserve return the same tuples as input
* @return object An object with tuples to be fetched, in order
*/
public static function multiGetClass($cls, $keyCol, array $keyVals, $skipNulls = true)
{
$obj = new $cls;
public static function multiGetClass(
string $cls,
string $keyCol,
array $keyVals,
bool $skipNulls,
bool $preserve
): object {
$obj = new $cls();
// PHP compatible datatype for settype() below
$colType = $obj->columnType($keyCol);
// Do not select anything extra
$obj->selectAdd();
$obj->selectAdd($obj->escapedTableName() . '.*');
if (!in_array($colType, array('integer', 'int'))) {
// This is because I'm afraid to escape strings incorrectly
// in the way we use them below in FIND_IN_SET for MariaDB
throw new ServerException('Cannot do multiGet on anything but integer columns');
// A PHP-compatible datatype to check against
$col_type = $obj->columnType($keyCol);
// The code below assumes one of the two results
if (!in_array($col_type, ['int', 'string'])) {
throw new ServerException(
'Cannot do multiGet on anything but integer or string columns'
);
}
if ($skipNulls) {
foreach ($keyVals as $key => $val) {
if (is_null($val)) {
unset($keyVals[$key]);
}
// Actually need to know if MariaDB or Oracle MySQL this time
$db_type = common_config('db', 'type');
if ($db_type === 'mysql') {
$tmp_obj = new $cls();
$tmp_obj->query('SELECT 0 /*M! + 1 */ AS is_mariadb;');
if ($tmp_obj->fetch() && $tmp_obj->is_mariadb) {
$db_type = 'mariadb';
}
}
$obj->whereAddIn($keyCol, $keyVals, $colType);
// Since we're inputting straight to a query: format and escape
foreach ($keyVals as $key => $val) {
settype($val, $colType);
$keyVals[$key] = $obj->escape($val);
$vals_escaped = [];
foreach (array_values($keyVals) as $i => $val) {
if (is_null($val)) {
$val_escaped = 'NULL';
} elseif ($col_type === 'int') {
$val_escaped = (string)(int) $val;
} else {
$val_escaped = "'{$obj->escape($val)}'";
}
if ($db_type !== 'mariadb') {
$vals_escaped[] = $val_escaped;
} else {
// A completely different approach for MariaDB (see below)
$vals_escaped[] = "({$val_escaped},{$i})";
}
}
// Check if values are ordered, makes sorting in SQL easier
$prev_val = reset($keyVals);
$order_asc = $order_desc = true;
foreach ($keyVals as $val) {
if ($val < $prev_val) {
$order_asc = false;
}
if ($val > $prev_val) {
$order_desc = false;
}
if ($order_asc === false && $order_desc === false) {
// One way to guarantee that there is no name collision
$join_tablename = common_database_tablename(
$obj->tableName() . '_vals'
);
$join_keyword = ($preserve ? 'RIGHT' : 'LEFT') . ' JOIN';
$vals_cast_type = ($col_type === 'int') ? 'INTEGER' : 'TEXT';
// A lot of magic to ensure we get an ordered reply with the same exact
// values as on input.
switch ($db_type) {
case 'pgsql':
// Explicit casting is done to cast empty arrays
$obj->_join = "\n" . sprintf(
<<<END
{$join_keyword} unnest(
CAST(ARRAY[%s] AS {$vals_cast_type}[])
) WITH ORDINALITY
AS {$join_tablename} ({$keyCol}, {$keyCol}_pos)
USING ({$keyCol})
END,
implode(',', $vals_escaped)
);
break;
}
$prev_val = $val;
case 'mariadb':
// Delivers an empty set
if (count($vals_escaped) == 0) {
$vals_escaped[] = '(NULL,0) LIMIT 0';
}
// MariaDB doesn't support JSON_TABLE, but Oracle MySQL does,
// which doesn't support VALUES without a ROW keyword though.
$obj->_join = "\n" . sprintf(
<<<END
{$join_keyword} (
WITH t1 ({$keyCol}, {$keyCol}_pos) AS (VALUES %s)
SELECT * FROM t1
) AS {$join_tablename} USING ({$keyCol})
END,
implode(',', $vals_escaped)
);
break;
case 'mysql':
default:
$obj->_join = "\n" . sprintf(
<<<END
{$join_keyword} JSON_TABLE(
JSON_ARRAY(%s), '$[*]' COLUMNS (
{$keyCol} {$vals_cast_type} PATH '$',
{$keyCol}_pos FOR ORDINALITY
)
) AS {$join_tablename} USING ({$keyCol})
END,
implode(',', $vals_escaped)
);
}
if ($order_asc) {
$obj->orderBy($keyCol);
} elseif ($order_desc) {
$obj->orderBy("{$keyCol} DESC");
} else {
switch (common_config('db', 'type')) {
case 'pgsql':
// "position" will make sure we keep the desired order
$obj->orderBy(sprintf(
"position(',' || CAST(%s AS text) || ',' IN ',%s,')",
$keyCol,
implode(',', $keyVals)
));
break;
case 'mysql':
// "find_in_set" will make sure we keep the desired order
$obj->orderBy(sprintf(
"find_in_set(%s, '%s')",
$keyCol,
implode(',', $keyVals)
));
break;
default:
throw new ServerException('Unknown DB type selected.');
}
if (!$preserve) {
// Implements a left semi-join
$obj->whereAdd("{$join_tablename}.{$keyCol}_pos IS NOT NULL");
}
// Filters both NULLs requested and non-matching NULLs
if ($skipNulls) {
$obj->whereAdd("{$obj->escapedTableName()}.{$keyCol} IS NOT NULL");
}
$obj->orderBy("{$join_tablename}.{$keyCol}_pos");
$obj->find();
return $obj;
}
@ -400,6 +444,11 @@ class Memcached_DataObject extends Safe_DataObject
return $result;
}
public function escapedTableName()
{
return common_database_tablename($this->tableName());
}
public function columnType($columnName)
{
$keys = $this->table();
@ -410,7 +459,7 @@ class Memcached_DataObject extends Safe_DataObject
$def = $keys[$columnName];
if ($def & DB_DATAOBJECT_INT) {
return 'integer';
return 'int';
} else {
return 'string';
}