be/src/service/client-request-state.h

// Licensed to the Apache Software Foundation (ASF) under one
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// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
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// with the License.  You may obtain a copy of the License at
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//   http://www.apache.org/licenses/LICENSE-2.0
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// Unless required by applicable law or agreed to in writing,
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// specific language governing permissions and limitations
// under the License.

#pragma once

#include "common/atomic.h"
#include "common/object-pool.h"
#include "common/status.h"
#include "exec/catalog-op-executor.h"
#include "runtime/timestamp-value.h"
#include "scheduling/query-schedule.h"
#include "service/child-query.h"
#include "service/impala-server.h"
#include "service/query-result-set.h"
#include "util/auth-util.h"
#include "util/condition-variable.h"
#include "util/runtime-profile.h"
#include "gen-cpp/Frontend_types.h"
#include "gen-cpp/ImpalaHiveServer2Service.h"

#include <boost/thread.hpp>
#include <boost/unordered_set.hpp>
#include <vector>

namespace impala {

class ClientRequestStateCleaner;
class Coordinator;
class ExecEnv;
class Expr;
class Frontend;
class ReportExecStatusRequestPB;
class RowBatch;
class RuntimeState;
class TRuntimeProfileTree;
class TupleRow;
enum class AdmissionOutcome;

/// Execution state of the client-facing side of a query. This captures everything
/// necessary to convert row batches received by the coordinator into results
/// we can return to the client. It also captures all state required for
/// servicing query-related requests from the client.
/// Thread safety: this class is generally not thread-safe, callers need to
/// synchronize access explicitly via lock(). See the ImpalaServer class comment for
/// the required lock acquisition order.
///
/// State Machine:
/// ExecState represents all possible states and UpdateNonErrorExecState /
/// UpdateQueryStatus defines all possible state transitions. ExecState starts out in the
/// INITIALIZED state and eventually transition to either the FINISHED or ERROR state. Any
/// state can transition to the ERROR state (if an error is hit or a timeout occurs). The
/// possible state transitions differ for a query depending on its type (e.g. depending on
/// the TStmtType). Successful QUERY / DML queries transition from INITIALIZED to PENDING
/// to RUNNING to FINISHED whereas DDL queries skip the PENDING phase.
///
/// TODO: Compute stats is the only stmt that requires child queries. Once the
/// CatalogService performs background stats gathering the concept of child queries
/// will likely become obsolete. Remove all child-query related code from this class.
class ClientRequestState {
 public:
  ClientRequestState(const TQueryCtx& query_ctx, ExecEnv* exec_env, Frontend* frontend,
      ImpalaServer* server, std::shared_ptr<ImpalaServer::SessionState> session);

  ~ClientRequestState();

  enum class ExecState {
    INITIALIZED, PENDING, RUNNING, FINISHED, ERROR
  };

  /// Sets the profile that is produced by the frontend. The frontend creates the
  /// profile during planning and returns it to the backend via TExecRequest,
  /// which then sets the frontend profile.
  void SetFrontendProfile(TRuntimeProfileNode profile);

  /// Based on query type, this either initiates execution of this ClientRequestState's
  /// TExecRequest or submits the query to the Admission controller for asynchronous
  /// admission control. When this returns the operation state is either RUNNING_STATE or
  /// PENDING_STATE.
  /// Non-blocking.
  /// Must *not* be called with lock_ held.
  Status Exec() WARN_UNUSED_RESULT;

  /// Execute a HiveServer2 metadata operation
  /// TODO: This is likely a superset of GetTableNames/GetDbs. Coalesce these different
  /// code paths.
  Status Exec(const TMetadataOpRequest& exec_request) WARN_UNUSED_RESULT;

  /// Call this to ensure that rows are ready when calling FetchRows(). Updates the
  /// query_status_, and advances operation_state_ to FINISHED or EXCEPTION. Must be
  /// preceded by call to Exec(). Waits for all child queries to complete. Takes lock_.
  /// Since this is a blocking operation, it is invoked from a separate thread
  /// (WaitAsync()) and all the callers that intend to block until Wait() completes
  /// are expected to use BlockOnWait().
  ///
  /// Logs the query events once the query reaches the FINISHED state. Threads blocked
  /// on Wait() are signalled *before* logging the events so that they can resume their
  /// execution (like fetching the results) and are not blocked until the event logging
  /// is complete.
  void Wait();

  /// Calls Wait() asynchronously in a thread and returns immediately.
  Status WaitAsync();

  /// BlockOnWait() may be called after WaitAsync() has been called in order to wait
  /// for the asynchronous thread (wait_thread_) to signal block_on_wait_cv_. It is
  /// thread-safe and all the caller threads will block until wait_thread_ has
  /// completed) and multiple times (non-blocking once wait_thread_ has completed).
  /// Do not call while holding lock_. 'timeout' is the amount of time (in microseconds)
  /// that the thread waits for WaitAsync() to complete before returning. If WaitAsync()
  /// completed within the timeout, this method returns true, false otherwise. A value of
  /// 0 causes this method to wait indefinitely. 'block_on_wait_time_us_' is the amount of
  /// time the client spent (in microseconds) waiting in BlockOnWait().
  bool BlockOnWait(int64_t timeout_us, int64_t* block_on_wait_time_us);

  /// Return at most max_rows from the current batch. If the entire current batch has
  /// been returned, fetch another batch first.
  /// Caller needs to hold fetch_rows_lock_ and lock_.
  /// Caller should verify that EOS has not be reached before calling.
  /// Must be preceeded by call to Wait() (or WaitAsync()/BlockOnWait()).
  /// Also updates operation_state_/query_status_ in case of error.
  /// 'block_on_wait_time_us' is the amount of time spent waiting in BlockOnWait(). It
  /// should be 0 if BlockOnWait() was never called.
  Status FetchRows(const int32_t max_rows, QueryResultSet* fetched_rows,
      int64_t block_on_wait_time_us) WARN_UNUSED_RESULT;

  /// Resets the state of this query such that the next fetch() returns results from the
  /// beginning of the query result set (by using the using result_cache_).
  /// It is valid to call this function for any type of statement that returns a result
  /// set, including queries, show stmts, compute stats, etc.
  /// Returns a recoverable error status if the restart is not possible, ok() otherwise.
  /// The error is recoverable to allow clients to resume fetching.
  /// The caller must hold fetch_rows_lock_ and lock_.
  Status RestartFetch() WARN_UNUSED_RESULT;

  /// Update operation state if the requested state isn't already obsolete. This is
  /// only for non-error states (PENDING, RUNNING and FINISHED) - if the query encounters
  /// an error the query status needs to be set with information about the error so
  /// UpdateQueryStatus() must be used instead. Takes lock_.
  void UpdateNonErrorExecState(ExecState exec_state);

  /// Update the query status and the "Query Status" summary profile string.
  /// If current status is already != ok, no update is made (we preserve the first error)
  /// If called with a non-ok argument, the expectation is that the query will be aborted
  /// quickly.
  /// Returns the status argument (so we can write
  /// RETURN_IF_ERROR(UpdateQueryStatus(SomeOperation())).
  /// Does not take lock_, but requires it: caller must ensure lock_
  /// is taken before calling UpdateQueryStatus
  Status UpdateQueryStatus(const Status& status) WARN_UNUSED_RESULT;

  /// Cancels the child queries and the coordinator with the given cause.
  /// If cause is NULL, it assume this was deliberately cancelled by the user while in
  /// FINISHED state. Otherwise, sets state to ERROR (TODO: IMPALA-1262: use CANCELLED).
  /// Does nothing if the query has reached EOS or already cancelled.
  ///
  /// Only returns an error if 'check_inflight' is true and the query is not yet
  /// in-flight. Otherwise, proceed and return Status::OK() even if the query isn't
  /// in-flight (for cleaning up after an error on the query issuing path).
  Status Cancel(bool check_inflight, const Status* cause) WARN_UNUSED_RESULT;

  /// This is called when the query is done (finished, cancelled, or failed).
  /// Takes lock_: callers must not hold lock() before calling.
  void Done();

  /// Sets the API-specific (Beeswax, HS2) result cache and its size bound.
  /// The given cache is owned by this client request state, even if an error is returned.
  /// Returns a non-ok status if max_size exceeds the per-impalad allowed maximum.
  Status SetResultCache(QueryResultSet* cache, int64_t max_size) WARN_UNUSED_RESULT;

  /// Wrappers around Coordinator::UpdateBackendExecStatus() and
  /// Coordinator::UpdateFilter() respectively for the coordinator object associated with
  /// 'this' ClientRequestState object. It ensures that these updates are applied to the
  /// coordinator even before it becomes accessible through GetCoordinator(). These
  /// methods should be used instead of calling them directly using the coordinator
  /// object.
  Status UpdateBackendExecStatus(const ReportExecStatusRequestPB& request,
      const TRuntimeProfileForest& thrift_profiles) WARN_UNUSED_RESULT;
  void UpdateFilter(const TUpdateFilterParams& params);

  /// Populate DML stats in 'dml_result' if this request succeeded.
  /// Sets 'query_status' to the overall query status.
  /// Return true if the result was set, otherwise return false.
  /// Caller must not hold 'lock()'.
  bool GetDmlStats(TDmlResult* dml_result, Status* query_status);

  /// Creates and sets the TExecRequest for the query associated with this
  /// ClientRequestState. The TExecRequest is created by the Impala frontend via the
  /// method Frontend::GetExecRequest(TQueryCtx, TExecRequest). The TQueryCtx is created
  /// by the ImpalaServer and contains the full query string
  /// (TQueryCtx::TClientRequest::stmt).
  Status InitExecRequest(const TQueryCtx& query_ctx);

  ImpalaServer::SessionState* session() const { return session_.get(); }

  /// Queries are run and authorized on behalf of the effective_user.
  const std::string& effective_user() const {
      return GetEffectiveUser(query_ctx_.session);
  }
  const std::string& connected_user() const { return query_ctx_.session.connected_user; }
  bool user_has_profile_access() const { return user_has_profile_access_; }
  const std::string& do_as_user() const { return query_ctx_.session.delegated_user; }
  TSessionType::type session_type() const { return query_ctx_.session.session_type; }
  const TUniqueId& session_id() const { return query_ctx_.session.session_id; }
  const std::string& default_db() const { return query_ctx_.session.database; }
  bool eos() const { return eos_; }
  const QuerySchedule* schedule() const { return schedule_.get(); }

  /// Returns the Coordinator for 'QUERY' and 'DML' requests once Coordinator::Exec()
  /// completes successfully. Otherwise returns null.
  Coordinator* GetCoordinator() const {
    return coord_exec_called_.Load() ? coord_.get() : nullptr;
  }

  /// Resource pool associated with this query, or an empty string if the schedule has not
  /// been created and had the pool set yet, or this StmtType doesn't go through admission
  /// control.
  /// Admission control resource pool associated with this query.
  std::string request_pool() const {
    return query_ctx_.__isset.request_pool ? query_ctx_.request_pool : "";
  }

  int num_rows_fetched() const { return num_rows_fetched_; }
  void set_fetched_rows() { fetched_rows_ = true; }
  bool fetched_rows() const { return fetched_rows_; }
  bool returns_result_set() { return !result_metadata_.columns.empty(); }
  const TResultSetMetadata* result_metadata() const { return &result_metadata_; }
  const TUniqueId& query_id() const { return query_ctx_.query_id; }
  /// Returns the TExecRequest for the query associated with this ClientRequestState.
  /// Contents are only valid after InitExecRequest(TQueryCtx) initializes the
  /// TExecRequest.
  const TExecRequest& exec_request() const {
    return exec_request_;
  }
  TStmtType::type stmt_type() const { return exec_request_.stmt_type; }
  TCatalogOpType::type catalog_op_type() const {
    return exec_request_.catalog_op_request.op_type;
  }
  TDdlType::type ddl_type() const {
    return exec_request_.catalog_op_request.ddl_params.ddl_type;
  }
  boost::mutex* lock() { return &lock_; }
  boost::mutex* fetch_rows_lock() { return &fetch_rows_lock_; }
  /// ExecState is stored using an AtomicEnum, so reads do not require holding lock_.
  ExecState exec_state() const { return exec_state_.Load(); }
  /// Translate exec_state_ to a TOperationState.
  apache::hive::service::cli::thrift::TOperationState::type TOperationState() const;
  /// Translate exec_state_ to a beeswax::QueryState.
  beeswax::QueryState::type BeeswaxQueryState() const;
  const Status& query_status() const { return query_status_; }
  void set_result_metadata(const TResultSetMetadata& md) { result_metadata_ = md; }
  void set_user_profile_access(bool user_has_profile_access) {
    user_has_profile_access_ = user_has_profile_access;
  }
  const RuntimeProfile* profile() const { return profile_; }
  const RuntimeProfile* summary_profile() const { return summary_profile_; }
  int64_t start_time_us() const { return start_time_us_; }
  int64_t end_time_us() const { return end_time_us_.Load(); }
  const std::string& sql_stmt() const { return query_ctx_.client_request.stmt; }
  const TQueryOptions& query_options() const {
    return query_ctx_.client_request.query_options;
  }
  /// Returns 0:0 if this is a root query
  TUniqueId parent_query_id() const { return query_ctx_.parent_query_id; }

  const std::vector<std::string>& GetAnalysisWarnings() const {
    return exec_request_.analysis_warnings;
  }

  inline int64_t last_active_ms() const {
    boost::lock_guard<boost::mutex> l(expiration_data_lock_);
    return last_active_time_ms_;
  }

  /// Returns true if Impala is actively processing this query.
  inline bool is_active() const {
    boost::lock_guard<boost::mutex> l(expiration_data_lock_);
    return ref_count_ > 0;
  }

  bool is_expired() const {
    boost::lock_guard<boost::mutex> l(expiration_data_lock_);
    return is_expired_;
  }

  void set_expired() {
    boost::lock_guard<boost::mutex> l(expiration_data_lock_);
    is_expired_ = true;
  }

  RuntimeProfile::EventSequence* query_events() const { return query_events_; }
  RuntimeProfile* summary_profile() { return summary_profile_; }

  /// Returns nullptr when catalog_op_type is not DDL.
  const TDdlExecResponse* ddl_exec_response() const {
    return catalog_op_executor_->ddl_exec_response();
  }

  /// Returns the FETCH_ROWS_TIMEOUT_MS value for this query (converted to microseconds).
  int64_t fetch_rows_timeout_us() const { return fetch_rows_timeout_us_; }

protected:
  /// Updates the end_time_us_ of this query if it isn't set. The end time is determined
  /// when this function is called for the first time, calling it multiple times does not
  /// change the end time.
  void UpdateEndTime();

 private:
  /// The coordinator is a friend class because it needs to be able to call
  /// UpdateEndTime() when a query's admission control resources are released.
  friend class Coordinator;

  const TQueryCtx query_ctx_;

  /// Ensures single-threaded execution of FetchRows(). Callers of FetchRows() are
  /// responsible for acquiring this lock. To avoid deadlocks, callers must not hold lock_
  /// while acquiring this lock (since FetchRows() will release and re-acquire lock_ during
  /// its execution).
  /// See "Locking" in the class comment for lock acquisition order.
  boost::mutex fetch_rows_lock_;

  /// Protects last_active_time_ms_, ref_count_ and is_expired_. Only held during short
  /// function calls - no other locks should be acquired while holding this lock.
  mutable boost::mutex expiration_data_lock_;

  /// Stores the last time that the query was actively doing work, in Unix milliseconds.
  int64_t last_active_time_ms_;

  /// ref_count_ > 0 if Impala is currently performing work on this query's behalf. Every
  /// time a client instructs Impala to do work on behalf of this query, the ref count is
  /// increased, and decreased once that work is completed.
  uint32_t ref_count_ = 0;

  /// True if the query expired by timing out.
  bool is_expired_ = false;

  /// True if there was a transaction and it got committed or aborted.
  bool transaction_closed_ = false;

  /// Executor for any child queries (e.g. compute stats subqueries). Always non-NULL.
  const boost::scoped_ptr<ChildQueryExecutor> child_query_executor_;

  /// Promise used by the admission controller. AdmissionController:AdmitQuery() will
  /// block on this promise until the query is either rejected, admitted, times out, or is
  /// cancelled. Can be set to CANCELLED by the ClientRequestState in order to cancel, but
  /// otherwise is set by AdmissionController with the admission decision.
  Promise<AdmissionOutcome, PromiseMode::MULTIPLE_PRODUCER> admit_outcome_;

  /// Protects all following fields. Acquirers should be careful not to hold it for too
  /// long, e.g. during RPCs because this lock is required to make progress on various
  /// ImpalaServer requests. If held for too long it can block progress of client
  /// requests for this query, e.g. query status and cancellation. Furthermore, until
  /// IMPALA-3882 is fixed, it can indirectly block progress on all other queries.
  /// See "Locking" in the class comment for lock acquisition order.
  boost::mutex lock_;

  /// TODO: remove and use ExecEnv::GetInstance() instead
  ExecEnv* exec_env_;

  /// Thread for asynchronously running Wait().
  std::unique_ptr<Thread> wait_thread_;

  /// Condition variable used to signal the threads that are blocked on Wait() to finish.
  /// Callers are expected to use BlockOnWait() for Wait() to finish.
  ConditionVariable block_on_wait_cv_;

  /// Wait condition used in conjunction with block_on_wait_cv_.
  bool is_wait_done_ = false;

  /// Session that this query is from
  std::shared_ptr<ImpalaServer::SessionState> session_;

  /// Resource assignment determined by scheduler. Owned by obj_pool_.
  std::unique_ptr<QuerySchedule> schedule_;

  /// Thread for asynchronously running the admission control code-path and starting
  /// execution in the following cases:
  /// 1. exec_request().stmt_type == QUERY or DML.
  /// 2. CTAS query for creating a table that does not exist.
  std::unique_ptr<Thread> async_exec_thread_;

  /// Set by the async-exec-thread after successful admission. Accessed through
  /// GetCoordinator() since most Coordinator methods can be called only after
  /// Coordinator::Exec() returns success. The only exceptions to this are
  /// FinishExecQueryOrDmlRequest(), which initializes it, calls Exec() on it and sets
  /// 'coord_exec_called_' to true, and UpdateBackendExecStatus() and UpdateFilter(),
  /// which can be called before Coordinator::Exec() returns.
  boost::scoped_ptr<Coordinator> coord_;

  /// Used by GetCoordinator() to check if 'coord_' can be made accessible. Set to true by
  /// the async-exec-thread only after Exec() has been successfully called on 'coord_'.
  AtomicBool coord_exec_called_;

  /// Runs statements that query or modify the catalog via the CatalogService.
  boost::scoped_ptr<CatalogOpExecutor> catalog_op_executor_;

  /// Result set used for requests that return results and are not QUERY
  /// statements. For example, EXPLAIN, LOAD, and SHOW use this.
  boost::scoped_ptr<std::vector<TResultRow>> request_result_set_;

  /// Cache of the first result_cache_max_size_ query results to allow clients to restart
  /// fetching from the beginning of the result set. This cache is appended to in
  /// FetchInternal(), and set to NULL if its bound is exceeded. If the bound is exceeded,
  /// then clients cannot restart fetching because some results have been lost since the
  /// last fetch. Only set if result_cache_max_size_ > 0.
  boost::scoped_ptr<QueryResultSet> result_cache_;

  /// Max size of the result_cache_ in number of rows. A value <= 0 means no caching.
  int64_t result_cache_max_size_ = -1;

  ObjectPool profile_pool_;

  /// The ClientRequestState builds three separate profiles.
  /// * profile_ is the top-level profile which houses the other
  ///   profiles, plus the query timeline
  /// * frontend_profile_ is the profile emitted by the frontend
  ///   during planning. Added to summary_profile_ so as to avoid
  ///   breaking other tools that depend on the profile_ layout.
  /// * summary_profile_ contains mostly static information about the
  ///   query, including the query statement, the plan and the user who submitted it.
  /// * server_profile_ tracks time spent inside the ImpalaServer,
  ///   but not inside fragment execution, i.e. the time taken to
  ///   register and set-up the query and for rows to be fetched.
  ///
  /// There's a fourth profile which is not built here (but is a
  /// child of profile_); the execution profile which tracks the
  /// actual fragment execution.
  ///
  /// Redaction: Only the following info strings in the profile are redacted as they
  /// are expected to contain sensitive information like schema/column references etc.
  /// Other fields are left unredacted.
  /// - Query Statement
  /// - Query Plan
  /// - Query Status
  /// - Error logs
  RuntimeProfile* const profile_;
  RuntimeProfile* const frontend_profile_;
  RuntimeProfile* const server_profile_;
  RuntimeProfile* const summary_profile_;

  /// Tracks the time spent materializing rows and converting them into a QueryResultSet.
  /// The QueryResultSet format used depends on the client, for Beeswax clients an ASCII
  /// representation is used, whereas for HS2 clients (using TCLIService.thrift) rows are
  /// converted into a TRowSet. Materializing rows includes evaluating any yet unevaluated
  /// expressions using ScalarExprEvaluators.
  RuntimeProfile::Counter* row_materialization_timer_;

  /// Tracks the rate that rows are materialized.
  RuntimeProfile::Counter* row_materialization_rate_;

  /// Tracks how long we are idle waiting for a client to fetch rows.
  RuntimeProfile::Counter* client_wait_timer_;
  /// Timer to track idle time for the above counter.
  MonotonicStopWatch client_wait_sw_;

  RuntimeProfile::EventSequence* query_events_;

  bool is_cancelled_ = false; // if true, Cancel() was called.
  bool eos_ = false;  // if true, there are no more rows to return

  /// We enforce the invariant that query_status_ is not OK iff exec_state_ is ERROR,
  /// given that lock_ is held. exec_state_ should only be updated using
  /// UpdateExecState(), to ensure that the query profile is also updated.
  AtomicEnum<ExecState> exec_state_{ExecState::INITIALIZED};

  /// The current status of the query tracked by this ClientRequestState. Updated by
  /// UpdateQueryStatus(Status).
  Status query_status_;

  /// The TExecRequest for the query tracked by this ClientRequestState. The TExecRequest
  /// is initialized in InitExecRequest(TQueryCtx). It should not be used until
  /// InitExecRequest(TQueryCtx) has been called.
  TExecRequest exec_request_;

  /// If true, effective_user() has access to the runtime profile and execution
  /// summary.
  bool user_has_profile_access_ = true;

  TResultSetMetadata result_metadata_; // metadata for select query
  int num_rows_fetched_ = 0; // number of rows fetched by client for the entire query

  /// The total number of rows fetched for this query, the counter is not reset if the
  /// fetch is restarted. It does not include any rows read from the results cache. It
  /// only counts the number of materialized rows and it is used for deriving the
  /// row_materialization_rate_. It is not set for non QUERY statements such as EXPLAIN,
  /// SHOW, etc.
  RuntimeProfile::Counter* num_rows_fetched_counter_ = nullptr;

  /// Similar to the 'num_rows_fetched_counter_' except it tracks the number of rows read
  /// from the results cache. The counter is not reset if the fetch is restarted and it
  /// is not set for non QUERY statements.
  RuntimeProfile::Counter* num_rows_fetched_from_cache_counter_ = nullptr;

  /// True if a fetch was attempted by a client, regardless of whether a result set
  /// (or error) was returned to the client.
  bool fetched_rows_ = false;

  /// To get access to UpdateCatalog, LOAD, and DDL methods. Not owned.
  Frontend* frontend_;

  /// The parent ImpalaServer; called to wait until the impalad has processed a catalog
  /// update request. Not owned.
  ImpalaServer* parent_server_;

  /// Start/end time of the query, in Unix microseconds.
  int64_t start_time_us_;
  /// end_time_us_ is initialized to 0, which is used to indicate that the query is not
  /// yet done. It is assinged the final value in ClientRequestState::Done() or when the
  /// coordinator relases its admission control resources.
  AtomicInt64 end_time_us_{0};

  /// Timeout, in microseconds, when waiting for rows to become available. Derived from
  /// the query option FETCH_ROWS_TIMEOUT_MS.
  const int64_t fetch_rows_timeout_us_;

  /// Executes a local catalog operation (an operation that does not need to execute
  /// against the catalog service). Includes USE, SHOW, DESCRIBE, and EXPLAIN statements.
  Status ExecLocalCatalogOp(const TCatalogOpRequest& catalog_op) WARN_UNUSED_RESULT;

  /// Updates last_active_time_ms_ and ref_count_ to reflect that query is currently not
  /// doing any work. Takes expiration_data_lock_.
  void MarkInactive();

  /// Updates last_active_time_ms_ and ref_count_ to reflect that query is currently being
  /// actively processed. Takes expiration_data_lock_.
  void MarkActive();

  /// Sets up profile and pre-execution counters, creates the query schedule, and spawns
  /// a thread that calls FinishExecQueryOrDmlRequest() which contains the core logic of
  /// executing a QUERY or DML execution request.
  /// Non-blocking.
  Status ExecAsyncQueryOrDmlRequest(const TQueryExecRequest& query_exec_request)
      WARN_UNUSED_RESULT;

  /// Submits the QuerySchedule to the admission controller and on successful admission,
  /// starts up the coordinator execution, makes it accessible by setting
  /// 'coord_exec_called_' to true and advances operation_state_ to RUNNING. Handles
  /// async cancellation of queries and cleans up state if needed.
  void FinishExecQueryOrDmlRequest();

  /// Core logic of executing a ddl statement. May internally initiate execution of
  /// queries (e.g., compute stats) or dml (e.g., create table as select)
  Status ExecDdlRequest() WARN_UNUSED_RESULT;

  /// Executes a shut down request.
  Status ExecShutdownRequest() WARN_UNUSED_RESULT;

  /// Core logic of Wait(). Does not update operation_state_/query_status_.
  Status WaitInternal() WARN_UNUSED_RESULT;

  /// Core logic of FetchRows(). Does not update operation_state_/query_status_.
  /// Caller needs to hold fetch_rows_lock_ and lock_. 'block_on_wait_time_us_' is the
  /// amount of time the client spent (in microseconds) waiting in BlockOnWait().
  Status FetchRowsInternal(const int32_t max_rows, QueryResultSet* fetched_rows,
      int64_t block_on_wait_time_us) WARN_UNUSED_RESULT;

  /// Gather and publish all required updates to the metastore.
  /// For transactional queries:
  /// If everything goes well the transaction is committed by the Catalogd.
  /// If an error occurs the transaction gets aborted by this function. Either way
  /// the transaction will be closed when this function returns.
  Status UpdateCatalog() WARN_UNUSED_RESULT;

  /// Copies results into request_result_set_
  /// TODO: Have the FE return list<Data.TResultRow> so that this isn't necessary
  void SetResultSet(const TDdlExecResponse* ddl_resp);
  void SetResultSet(const std::vector<std::string>& results);
  void SetResultSet(const std::vector<std::string>& col1,
      const std::vector<std::string>& col2);
  void SetResultSet(const vector<string>& col1,
      const vector<string>& col2, const vector<string>& col3);
  void SetResultSet(const std::vector<std::string>& col1,
      const std::vector<std::string>& col2, const std::vector<std::string>& col3,
      const std::vector<std::string>& col4);

  /// Sets the result set for a CREATE TABLE AS SELECT statement. The results will not be
  /// ready until all BEs complete execution. This can be called as part of Wait(),
  /// at which point results will be available.
  void SetCreateTableAsSelectResultSet();

  /// Updates the metastore's table and column statistics based on the child-query results
  /// of a compute stats command.
  /// TODO: Unify the various ways that the Metastore is updated for DDL/DML.
  /// For example, INSERT queries update partition metadata in UpdateCatalog() using a
  /// TUpdateCatalogRequest, whereas our DDL uses a TCatalogOpRequest for very similar
  /// purposes. Perhaps INSERT should use a TCatalogOpRequest as well.
  Status UpdateTableAndColumnStats(const std::vector<ChildQuery*>& child_queries)
      WARN_UNUSED_RESULT;

  /// Sets result_cache_ to NULL and updates its associated metrics and mem consumption.
  /// This function is a no-op if the cache has already been cleared.
  void ClearResultCache();

  /// Update the operation state and the "Query State" summary profile string.
  /// Does not take lock_, but requires it: caller must ensure lock_ is taken before
  /// calling UpdateExecState.
  void UpdateExecState(ExecState exec_state);

  /// Gets the query options, their levels and the values for this client request
  /// and populates the result set with them. It covers the subset of options for
  /// 'SET' and all of them for 'SET ALL'
  void PopulateResultForSet(bool is_set_all);

  /// Returns the transaction id for this client request. 'InTransaction()' must be
  /// true when invoked.
  int64_t GetTransactionId() const;

  /// Returns true if there is an open transaction for this client request.
  bool InTransaction() const;

  /// Aborts the transaction of this client request.
  void AbortTransaction();

  /// Invoke this function when the transaction is committed or aborted.
  void ClearTransactionState();

  /// helper that logs the audit record for this query id. Takes the query_status
  /// as input parameter so that it operates on the same status polled in the
  /// beginning of LogQueryEvents().
  Status LogAuditRecord(const Status& query_status) WARN_UNUSED_RESULT;

  /// Helper that logs the lineage record for this query id.
  Status LogLineageRecord() WARN_UNUSED_RESULT;

  /// Logs audit and column lineage events. Expects that Wait() has already finished.
  /// Grabs lock_ for polling the query_status(). Hence do not call it under lock_.
  void LogQueryEvents();

  /// Converts the given ExecState to a string representation.
  std::string ExecStateToString(ExecState state) const;
};

}