Add comments to trace_replay.h (#5359)
Summary: Add file, class, and function level comments in trace_replay.h Pull Request resolved: https://github.com/facebook/rocksdb/pull/5359 Differential Revision: D15505318 Pulled By: sagar0 fbshipit-source-id: 181e3d4ea805fd9a33f91b89e123bbd0c1ead2ce
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@ -15,6 +15,9 @@
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namespace rocksdb {
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// This file contains Tracer and Replayer classes that enable capturing and
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// replaying RocksDB traces.
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class ColumnFamilyHandle;
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class ColumnFamilyData;
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class DB;
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@ -29,6 +32,7 @@ const unsigned int kTracePayloadLengthSize = 4;
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const unsigned int kTraceMetadataSize =
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kTraceTimestampSize + kTraceTypeSize + kTracePayloadLengthSize;
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// Supported Trace types.
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enum TraceType : char {
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kTraceBegin = 1,
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kTraceEnd = 2,
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@ -36,13 +40,16 @@ enum TraceType : char {
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kTraceGet = 4,
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kTraceIteratorSeek = 5,
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kTraceIteratorSeekForPrev = 6,
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// All trace types should be added before kTraceMax
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kTraceMax,
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};
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// TODO: This should also be made part of public interface to help users build
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// custom TracerReaders and TraceWriters.
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//
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// The data structure that defines a single trace.
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struct Trace {
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uint64_t ts;
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uint64_t ts; // timestamp
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TraceType type;
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std::string payload;
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@ -53,25 +60,47 @@ struct Trace {
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}
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};
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// Trace RocksDB operations using a TraceWriter.
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// Tracer captures all RocksDB operations using a user-provided TraceWriter.
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// Every RocksDB operation is written as a single trace. Each trace will have a
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// timestamp and type, followed by the trace payload.
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class Tracer {
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public:
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Tracer(Env* env, const TraceOptions& trace_options,
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std::unique_ptr<TraceWriter>&& trace_writer);
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~Tracer();
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// Trace all write operations -- Put, Merge, Delete, SingleDelete, Write
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Status Write(WriteBatch* write_batch);
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// Trace Get operations.
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Status Get(ColumnFamilyHandle* cfname, const Slice& key);
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// Trace Iterators.
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Status IteratorSeek(const uint32_t& cf_id, const Slice& key);
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Status IteratorSeekForPrev(const uint32_t& cf_id, const Slice& key);
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// Returns true if the trace is over the configured max trace file limit.
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// False otherwise.
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bool IsTraceFileOverMax();
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// Writes a trace footer at the end of the tracing
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Status Close();
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private:
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// Write a trace header at the beginning, typically on initiating a trace,
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// with some metadata like a magic number, trace version, RocksDB version, and
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// trace format.
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Status WriteHeader();
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// Write a trace footer, typically on ending a trace, with some metadata.
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Status WriteFooter();
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// Write a single trace using the provided TraceWriter to the underlying
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// system, say, a filesystem or a streaming service.
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Status WriteTrace(const Trace& trace);
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// Helps in filtering and sampling of traces.
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// Returns true if a trace should be skipped, false otherwise.
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bool ShouldSkipTrace(const TraceType& type);
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Env* env_;
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@ -80,14 +109,24 @@ class Tracer {
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uint64_t trace_request_count_;
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};
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// Replay RocksDB operations from a trace.
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// Replayer helps to replay the captured RocksDB operations, using a user
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// provided TraceReader.
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// The Replayer is instantiated via db_bench today, on using "replay" benchmark.
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class Replayer {
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public:
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Replayer(DB* db, const std::vector<ColumnFamilyHandle*>& handles,
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std::unique_ptr<TraceReader>&& reader);
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~Replayer();
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// Replay all the traces from the provided trace stream, taking the delay
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// between the traces into consideration.
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Status Replay();
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// Enables fast forwarding a replay by reducing the delay between the ingested
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// traces.
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// fast_forward : Rate of replay speedup.
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// If 1, replay the operations at the same rate as in the trace stream.
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// If > 1, speed up the replay by this amount.
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Status SetFastForward(uint32_t fast_forward);
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private:
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