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improve comments in db_impl_secondary

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Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/5360

Differential Revision: D15502973

Pulled By: miasantreble

fbshipit-source-id: 15b7f9d7928e771a6fac0643861173be8ba6b37a
This commit is contained in:
Zhongyi Xie 2019-05-24 15:26:02 -07:00 committed by Facebook Github Bot
parent 029b98984e
commit a466120cd5
2 changed files with 16 additions and 2 deletions
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2
db/db_impl_secondary.cc
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@ -120,8 +120,6 @@ Status DBImplSecondary::FindNewLogNumbers(std::vector<uint64_t>* logs) {
return s; return s;
} }
// try to find log reader using log_number from log_readers_ map, initialize
// if it doesn't exist
Status DBImplSecondary::MaybeInitLogReader( Status DBImplSecondary::MaybeInitLogReader(
uint64_t log_number, log::FragmentBufferedReader** log_reader) { uint64_t log_number, log::FragmentBufferedReader** log_reader) {
auto iter = log_readers_.find(log_number); auto iter = log_readers_.find(log_number);

16
db/db_impl_secondary.h
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@ -13,6 +13,7 @@
namespace rocksdb { namespace rocksdb {
// A wrapper class to hold log reader, log reporter, log status.
class LogReaderContainer { class LogReaderContainer {
public: public:
LogReaderContainer() LogReaderContainer()
@ -62,11 +63,19 @@ class LogReaderContainer {
}; };
}; };
// The secondary instance shares access to the storage as the primary.
// The secondary is able to read and replay changes described in both the
// MANIFEST and the WAL files without coordination with the primary.
// The secondary instance can be opened using `DB::OpenAsSecondary`. After
// that, it can call `DBImplSecondary::TryCatchUpWithPrimary` to make best
// effort attempts to catch up with the primary.
class DBImplSecondary : public DBImpl { class DBImplSecondary : public DBImpl {
public: public:
DBImplSecondary(const DBOptions& options, const std::string& dbname); DBImplSecondary(const DBOptions& options, const std::string& dbname);
~DBImplSecondary() override; ~DBImplSecondary() override;
// Recover by replaying MANIFEST and WAL. Also initialize manifest_reader_
// and log_readers_ to facilitate future operations.
Status Recover(const std::vector<ColumnFamilyDescriptor>& column_families, Status Recover(const std::vector<ColumnFamilyDescriptor>& column_families,
bool read_only, bool error_if_log_file_exist, bool read_only, bool error_if_log_file_exist,
bool error_if_data_exists_in_logs) override; bool error_if_data_exists_in_logs) override;
@ -182,10 +191,15 @@ class DBImplSecondary : public DBImpl {
// method can take long time due to all the I/O and CPU costs. // method can take long time due to all the I/O and CPU costs.
Status TryCatchUpWithPrimary() override; Status TryCatchUpWithPrimary() override;
// Try to find log reader using log_number from log_readers_ map, initialize
// if it doesn't exist
Status MaybeInitLogReader(uint64_t log_number, Status MaybeInitLogReader(uint64_t log_number,
log::FragmentBufferedReader** log_reader); log::FragmentBufferedReader** log_reader);
protected: protected:
// ColumnFamilyCollector is a write batch handler which does nothing
// except recording unique column family IDs
class ColumnFamilyCollector : public WriteBatch::Handler { class ColumnFamilyCollector : public WriteBatch::Handler {
std::unordered_set<uint32_t> column_family_ids_; std::unordered_set<uint32_t> column_family_ids_;
@ -262,6 +276,8 @@ class DBImplSecondary : public DBImpl {
std::unordered_set<ColumnFamilyData*>* cfds_changed, std::unordered_set<ColumnFamilyData*>* cfds_changed,
JobContext* job_context); JobContext* job_context);
Status FindNewLogNumbers(std::vector<uint64_t>* logs); Status FindNewLogNumbers(std::vector<uint64_t>* logs);
// After manifest recovery, replay WALs and refresh log_readers_ if necessary
// REQUIRES: log_numbers are sorted in ascending order
Status RecoverLogFiles(const std::vector<uint64_t>& log_numbers, Status RecoverLogFiles(const std::vector<uint64_t>& log_numbers,
SequenceNumber* next_sequence, SequenceNumber* next_sequence,
std::unordered_set<ColumnFamilyData*>* cfds_changed, std::unordered_set<ColumnFamilyData*>* cfds_changed,