// time has been spent to make sure the cache performs appropriately for
// respective storage medium.
// The file defines
-// PersistentCacheOptions : Options for persistent cache
// PersistentCacheTier : Implementation that handles individual cache tier
// PersistentTieresCache : Implementation that handles all tiers as a logical
// unit
// null
namespace rocksdb {
-// Persistent Cache Options
-//
-// This struct captures all the options that are used to configure persistent
-// cache. Some of the terminologies used in naming the options are
-//
-// dispatch size :
-// This is the size in which IO is dispatched to the device
-//
-// write buffer size :
-// This is the size of an individual write buffer size. Write buffers are
-// grouped to form buffered file.
-//
-// cache size :
-// This is the logical maximum for the cache size
-//
-// qdepth :
-// This is the max number of IOs that can issues to the device in parallel
-//
-// pepeling :
-// The writer code path follows pipelined architecture, which means the
-// operations are handed off from one stage to another
-//
-// pipelining backlog size :
-// With the pipelined architecture, there can always be backlogging of ops in
-// pipeline queues. This is the maximum backlog size after which ops are dropped
-// from queue
-struct PersistentCacheOptions {
- explicit PersistentCacheOptions(Env* const _env, const std::string& _path,
- const uint64_t _cache_size,
- const std::shared_ptr<Logger>& _log,
- const uint32_t _write_buffer_size = 1 * 1024 *
- 1024) {
- env = _env;
- path = _path;
- log = _log;
- cache_size = _cache_size;
- writer_dispatch_size = write_buffer_size = _write_buffer_size;
- }
-
- //
- // Validate the settings. Our intentions are to catch erroneous settings ahead
- // of time instead going violating invariants or causing dead locks.
- //
- Status ValidateSettings() const {
- // (1) check pre-conditions for variables
- if (!env || path.empty()) {
- return Status::InvalidArgument("empty or null args");
- }
-
- // (2) assert size related invariants
- // - cache size cannot be less than cache file size
- // - individual write buffer size cannot be greater than cache file size
- // - total write buffer size cannot be less than 2X cache file size
- if (cache_size < cache_file_size || write_buffer_size >= cache_file_size ||
- write_buffer_size * write_buffer_count() < 2 * cache_file_size) {
- return Status::InvalidArgument("invalid cache size");
- }
-
- // (2) check writer settings
- // - Queue depth cannot be 0
- // - writer_dispatch_size cannot be greater than writer_buffer_size
- // - dispatch size and buffer size need to be aligned
- if (!writer_qdepth || writer_dispatch_size > write_buffer_size ||
- write_buffer_size % writer_dispatch_size) {
- return Status::InvalidArgument("invalid writer settings");
- }
-
- return Status::OK();
- }
-
- //
- // Env abstraction to use for systmer level operations
- //
- Env* env;
-
- //
- // Path for the block cache where blocks are persisted
- //
- std::string path;
-
- //
- // Log handle for logging messages
- //
- std::shared_ptr<Logger> log;
-
- //
- // Logical cache size
- //
- uint64_t cache_size = std::numeric_limits<uint64_t>::max();
-
- // cache-file-size
- //
- // Cache consists of multiples of small files. This parameter defines the
- // size of an individual cache file
- //
- // default: 1M
- uint32_t cache_file_size = 100ULL * 1024 * 1024;
-
- // writer-qdepth
- //
- // The writers can issues IO to the devices in parallel. This parameter
- // controls the max number if IOs that can issues in parallel to the block
- // device
- //
- // default :1
- uint32_t writer_qdepth = 1;
-
- // pipeline-writes
- //
- // The write optionally follow pipelined architecture. This helps
- // avoid regression in the eviction code path of the primary tier. This
- // parameter defines if pipelining is enabled or disabled
- //
- // default: true
- bool pipeline_writes_ = true;
-
- // max-write-pipeline-backlog-size
- //
- // Max pipeline buffer size. This is the maximum backlog we can accumulate
- // while waiting for writes. After the limit, new ops will be dropped.
- //
- // Default: 1GiB
- uint64_t max_write_pipeline_backlog_size = 1ULL * 1024 * 1024 * 1024;
-
- // write-buffer-size
- //
- // This is the size in which buffer slabs are allocated.
- //
- // Default: 1M
- uint32_t write_buffer_size = 1ULL * 1024 * 1024;
-
- // write-buffer-count
- //
- // This is the total number of buffer slabs. This is calculated as a factor of
- // file size in order to avoid dead lock.
- size_t write_buffer_count() const {
- assert(write_buffer_size);
- return static_cast<size_t>((writer_qdepth + 1.2) * cache_file_size /
- write_buffer_size);
- }
-
- // writer-dispatch-size
- //
- // The writer thread will dispatch the IO at the specified IO size
- //
- // default: 1M
- uint64_t writer_dispatch_size = 1ULL * 1024 * 1024;
-
- PersistentCacheOptions MakePersistentCacheOptions(
- const std::string& path, const uint64_t size,
- const std::shared_ptr<Logger>& log);
-};
-
// Persistent Cache Tier
//
// This a logical abstraction that defines a tier of the persistent cache. Tiers
projects / rocksdb.git / commitdiff