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authorJohn Firebaugh <john.firebaugh@gmail.com>2016-02-09 17:19:27 -0800
committerJohn Firebaugh <john.firebaugh@gmail.com>2016-02-10 15:40:20 -0800
commitdb3620c58f0c3351e26b0e3bcfd23ff414f829a1 (patch)
treee8def564e12307a997270b66a4ed46b68f5e13a4 /include
parent591012401072e63b89071787d90bf5ae4362dca1 (diff)
downloadqtlocation-mapboxgl-db3620c58f0c3351e26b0e3bcfd23ff414f829a1.tar.gz
[core] Implement an eviction policy for OfflineDatabase
When inserting an cached resource, or removing a region, remove least-recently used resources and tiles, not used by offline regions, until the used database size, as calculated by multiplying the number of in-use pages by the page size, is less than the maximum cache size minus 5 times the page size. In addition, OfflineDatabase may be configured to ignore cache puts of individual resources larger than a certain size. This policy is similar but not identical to the former SQLiteCache policy: * It accounts for offline, by exempting resources required by offline regions from eviction. * It must delete from two tables (resources and tiles), rather than one. Currently the strategy is naive: evict 50 rows at a time from each table. * It makes maximumCacheSize and maximumCacheEntrySize completely independent. The SQLiteCache implementation evicted when `usedSize > maximumCacheSize - 2 * maximumCacheEntrySize`. This evicts when `usedSize > maximumCacheSize - 5 * pageSize`. * It uses a non-unlimited default value for maximumCacheSize: 50 MB. We should have always had a limit in place; "a cache without an eviction policy is a resource leak".
Diffstat (limited to 'include')
-rw-r--r--include/mbgl/storage/default_file_source.hpp29
-rw-r--r--include/mbgl/util/constants.hpp3
2 files changed, 12 insertions, 20 deletions
diff --git a/include/mbgl/storage/default_file_source.hpp b/include/mbgl/storage/default_file_source.hpp
index e7ffe125b1..0cee7de328 100644
--- a/include/mbgl/storage/default_file_source.hpp
+++ b/include/mbgl/storage/default_file_source.hpp
@@ -3,6 +3,7 @@
#include <mbgl/storage/file_source.hpp>
#include <mbgl/storage/offline.hpp>
+#include <mbgl/util/constants.hpp>
#include <vector>
@@ -14,15 +15,15 @@ template <typename T> class Thread;
class DefaultFileSource : public FileSource {
public:
- DefaultFileSource(const std::string& cachePath, const std::string& assetRoot);
+ DefaultFileSource(const std::string& cachePath,
+ const std::string& assetRoot,
+ uint64_t maximumCacheSize = util::DEFAULT_MAX_CACHE_SIZE,
+ uint64_t maximumCacheEntrySize = util::DEFAULT_MAX_CACHE_ENTRY_SIZE);
~DefaultFileSource() override;
void setAccessToken(const std::string&);
std::string getAccessToken() const;
- void setMaximumCacheSize(uint64_t size);
- void setMaximumCacheEntrySize(uint64_t size);
-
std::unique_ptr<FileRequest> request(const Resource&, Callback) override;
/*
@@ -71,13 +72,11 @@ public:
optional<OfflineRegionStatus>)>) const;
/*
- * Initiate the removal of offline region from the database.
+ * Remove an offline region from the database and perform any resources evictions
+ * necessary as a result.
*
- * All resources required by the region, but not also required by other regions, will
- * become eligible for removal for space-optimization. Because the offline database is
- * also used for ambient usage-based caching, and offline resources may still be useful
- * for ambient usage, they are not immediately removed. To immediately remove resources
- * not used by any extant region, call removeUnusedOfflineResources().
+ * Eviction works by removing the least-recently requested resources not also required
+ * by other regions, until the database shrinks below a certain size.
*
* Note that this method takes ownership of the input, reflecting the fact that once
* region deletion is initiated, it is not legal to perform further actions with the
@@ -89,16 +88,6 @@ public:
*/
void deleteOfflineRegion(OfflineRegion&&, std::function<void (std::exception_ptr)>);
- /*
- * Remove all resources in the database that are not required by any region, thus
- * optimizing the disk space used by the offline database.
- *
- * When the operation is complete or encounters an error, the given callback will be
- * executed on the database thread; it is the responsibility of the SDK bindings
- * to re-execute a user-provided callback on the main thread.
- */
- void removeUnusedOfflineResources(std::function<void (std::exception_ptr)>);
-
// For testing only.
void put(const Resource&, const Response&);
void goOffline();
diff --git a/include/mbgl/util/constants.hpp b/include/mbgl/util/constants.hpp
index 24f4b5ee72..667e2f8497 100644
--- a/include/mbgl/util/constants.hpp
+++ b/include/mbgl/util/constants.hpp
@@ -21,6 +21,9 @@ extern const double PITCH_MAX;
extern const double MIN_ZOOM;
extern const double MAX_ZOOM;
+extern const uint64_t DEFAULT_MAX_CACHE_SIZE;
+extern const uint64_t DEFAULT_MAX_CACHE_ENTRY_SIZE;
+
} // namespace util
namespace debug {