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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include <vespa/document/base/globalid.h>
namespace document::select {
class Node;
/**
* This class allows for very quickly and cheaply filtering away metadata
* entries that may not possibly match a document selection with a location
* predicate, based on nothing but the GIDs in the metadata. This avoids
* having to fetch the document IDs or whole documents themselves from
* potentially slow storage in order to evaluate the selection in full.
*/
class GidFilter {
public:
// GCC <= 5.3 has a bug where copying a boost::optional at certain -O
// levels causes a erroneous compiler warning.
// Using our own poor-man's optional for now.
// TODO: replace with std::otional once on a C++17 stdlib.
struct OptionalLocation {
uint32_t _location;
bool _valid;
OptionalLocation() : _location(0), _valid(false) {}
explicit OptionalLocation(uint32_t location)
: _location(location),
_valid(true)
{
}
};
private:
OptionalLocation _required_gid_location;
/**
* Lifetime of AST Node pointed to does not have to extend beyond the call
* to this constructor.
*/
explicit GidFilter(const Node& ast_root);
public:
/**
* No-op filter; everything matches always.
*/
GidFilter()
: _required_gid_location()
{
}
/**
* A GidFilter instance may be safely and cheaply copied. No dependencies
* exist on the life time of the AST from which it was created.
*/
GidFilter(const GidFilter&) = default;
GidFilter& operator=(const GidFilter&) = default;
/**
* Create a filter with a location inferred from the provided selection.
* If the selection does not contain a location predicate, the GidFilter
* will effectively act as a no-op which assumes every document may match.
*
* It is safe to use the resulting GidFilter even if the lifetime of the
* Node pointed to by ast_root does not extend beyond this call; the
* GidFilter does not store any implicit or explicit references to it.
*/
static GidFilter for_selection_root_node(const Node& ast_root) {
return GidFilter(ast_root);
}
/**
* Returns false iff there exists no way that a document whose ID has the
* given GID can possibly match the selection. This currently only applies
* if the document selection contains a location-based predicate (i.e.
* id.user or id.group).
*
* As the name implies this is a probabilistic match; it's possible for
* this function to return true even if the document selection matched
* against the full document/documentid would return false.
*/
bool gid_might_match_selection(const GlobalId& gid) const {
const uint32_t gid_location = gid.getLocationSpecificBits();
return (!_required_gid_location._valid
|| (gid_location == _required_gid_location._location));
}
};
}
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