andreacavalli/rocksdb
0
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

Add comments t get_context.h

Browse Source 
Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/5353

Differential Revision: D15497912

Pulled By: anand1976

fbshipit-source-id: 72cff2465ca342aa810f925be5a7016b938aa416
This commit is contained in:
anand76 2019-05-24 13:24:52 -07:00 committed by Facebook Github Bot
parent 6267ed251a
commit eb7647ee6c
1 changed files with 31 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
table/get_context.h
View File

@ -17,6 +17,9 @@ namespace rocksdb {
class MergeContext;
class PinnedIteratorsManager;
// Data structure for accumulating statistics during a point lookup. At the
// end of the point lookup, the corresponding ticker stats are updated. This
// avoids the overhead of frequent ticker stats updates
struct GetContextStats {
uint64_t num_cache_hit = 0;
uint64_t num_cache_index_hit = 0;
@ -41,8 +44,17 @@ struct GetContextStats {
uint64_t num_cache_compression_dict_bytes_insert = 0;
};
// A class to hold context about a point lookup, such as pointer to value
// slice, key, merge context etc, as well as the current state of the
// lookup. Any user using GetContext to track the lookup result must call
// SaveValue() whenever the internal key is found. This can happen
// repeatedly in case of merge operands. In case the key may exist with
// high probability, but IO is required to confirm and the user doesn't allow
// it, MarkKeyMayExist() must be called instead of SaveValue().
class GetContext {
public:
// Current state of the point lookup. All except kNotFound and kMerge are
// terminal states
enum GetState {
kNotFound,
kFound,
@ -53,6 +65,19 @@ class GetContext {
};
GetContextStats get_context_stats_;
// Constructor
// @param value_found If non-nullptr, set to false if key may be present
// but we can't be certain because we cannot do IO
// @param max_covering_tombstone_seq Pointer to highest sequence number of
// range deletion covering the key. When an internal key
// is found with smaller sequence number, the lookup
// terminates
// @param seq If non-nullptr, the sequence number of the found key will be
// saved here
// @param callback Pointer to ReadCallback to perform additional checks
// for visibility of a key
// @param is_blob_index If non-nullptr, will be used to indicate if a found
// key is of type blob index
GetContext(const Comparator* ucmp, const MergeOperator* merge_operator,
Logger* logger, Statistics* statistics, GetState init_state,
const Slice& user_key, PinnableSlice* value, bool* value_found,
@ -64,13 +89,15 @@ class GetContext {
GetContext() = default;
// This can be called to indicate that a key may be present, but cannot be
// confirmed due to IO not allowed
void MarkKeyMayExist();
// Records this key, value, and any meta-data (such as sequence number and
// state) into this GetContext.
//
// If the parsed_key matches the user key that we are looking for, sets
// mathced to true.
// matched to true.
//
// Returns True if more keys need to be read (due to merges) or
// False if the complete value has been found.
@ -133,6 +160,9 @@ class GetContext {
bool* is_blob_index_;
};
// Call this to replay a log and bring the get_context up to date. The replay
// log must have been created by another GetContext object, whose replay log
// must have been set by calling GetContext::SetReplayLog().
void replayGetContextLog(const Slice& replay_log, const Slice& user_key,
GetContext* get_context,
Cleanable* value_pinner = nullptr);