neon/safekeeper/src/timeline.rs

//! This module implements Timeline lifecycle management and has all necessary code
//! to glue together SafeKeeper and all other background services.

use anyhow::{anyhow, bail, Result};
use parking_lot::{Mutex, MutexGuard};
use postgres_ffi::XLogSegNo;

use std::cmp::max;
use std::path::PathBuf;
use std::sync::Arc;
use tokio::{
    sync::{mpsc::Sender, watch},
    time::Instant,
};
use tracing::*;
use utils::http::error::ApiError;
use utils::{
    id::{NodeId, TenantTimelineId},
    lsn::Lsn,
};

use storage_broker::proto::SafekeeperTimelineInfo;
use storage_broker::proto::TenantTimelineId as ProtoTenantTimelineId;

use crate::safekeeper::{
    AcceptorProposerMessage, ProposerAcceptorMessage, SafeKeeper, SafeKeeperState,
    SafekeeperMemState, ServerInfo, Term,
};
use crate::send_wal::WalSenders;
use crate::{control_file, safekeeper::UNKNOWN_SERVER_VERSION};

use crate::metrics::FullTimelineInfo;
use crate::wal_storage::Storage as wal_storage_iface;
use crate::SafeKeeperConf;
use crate::{debug_dump, wal_storage};

/// Things safekeeper should know about timeline state on peers.
#[derive(Debug, Clone)]
pub struct PeerInfo {
    pub sk_id: NodeId,
    /// Term of the last entry.
    _last_log_term: Term,
    /// LSN of the last record.
    _flush_lsn: Lsn,
    pub commit_lsn: Lsn,
    /// Since which LSN safekeeper has WAL. TODO: remove this once we fill new
    /// sk since backup_lsn.
    pub local_start_lsn: Lsn,
    /// When info was received.
    ts: Instant,
}

impl PeerInfo {
    fn from_sk_info(sk_info: &SafekeeperTimelineInfo, ts: Instant) -> PeerInfo {
        PeerInfo {
            sk_id: NodeId(sk_info.safekeeper_id),
            _last_log_term: sk_info.last_log_term,
            _flush_lsn: Lsn(sk_info.flush_lsn),
            commit_lsn: Lsn(sk_info.commit_lsn),
            local_start_lsn: Lsn(sk_info.local_start_lsn),
            ts,
        }
    }
}

// vector-based node id -> peer state map with very limited functionality we
// need.
#[derive(Debug, Clone, Default)]
pub struct PeersInfo(pub Vec<PeerInfo>);

impl PeersInfo {
    fn get(&mut self, id: NodeId) -> Option<&mut PeerInfo> {
        self.0.iter_mut().find(|p| p.sk_id == id)
    }

    fn upsert(&mut self, p: &PeerInfo) {
        match self.get(p.sk_id) {
            Some(rp) => *rp = p.clone(),
            None => self.0.push(p.clone()),
        }
    }
}

/// Shared state associated with database instance
pub struct SharedState {
    /// Safekeeper object
    sk: SafeKeeper<control_file::FileStorage, wal_storage::PhysicalStorage>,
    /// In memory list containing state of peers sent in latest messages from them.
    peers_info: PeersInfo,
    /// True when WAL backup launcher oversees the timeline, making sure WAL is
    /// offloaded, allows to bother launcher less.
    wal_backup_active: bool,
    /// True whenever there is at least some pending activity on timeline: live
    /// compute connection, pageserver is not caughtup (it must have latest WAL
    /// for new compute start) or WAL backuping is not finished. Practically it
    /// means safekeepers broadcast info to peers about the timeline, old WAL is
    /// trimmed.
    ///
    /// TODO: it might be better to remove tli completely from GlobalTimelines
    /// when tli is inactive instead of having this flag.
    active: bool,
    num_computes: u32,
    last_removed_segno: XLogSegNo,
}

impl SharedState {
    /// Initialize fresh timeline state without persisting anything to disk.
    fn create_new(
        conf: &SafeKeeperConf,
        ttid: &TenantTimelineId,
        state: SafeKeeperState,
    ) -> Result<Self> {
        if state.server.wal_seg_size == 0 {
            bail!(TimelineError::UninitializedWalSegSize(*ttid));
        }

        if state.server.pg_version == UNKNOWN_SERVER_VERSION {
            bail!(TimelineError::UninitialinzedPgVersion(*ttid));
        }

        if state.commit_lsn < state.local_start_lsn {
            bail!(
                "commit_lsn {} is higher than local_start_lsn {}",
                state.commit_lsn,
                state.local_start_lsn
            );
        }

        // We don't want to write anything to disk, because we may have existing timeline there.
        // These functions should not change anything on disk.
        let control_store = control_file::FileStorage::create_new(ttid, conf, state)?;
        let wal_store =
            wal_storage::PhysicalStorage::new(ttid, conf.timeline_dir(ttid), conf, &control_store)?;
        let sk = SafeKeeper::new(control_store, wal_store, conf.my_id)?;

        Ok(Self {
            sk,
            peers_info: PeersInfo(vec![]),
            wal_backup_active: false,
            active: false,
            num_computes: 0,
            last_removed_segno: 0,
        })
    }

    /// Restore SharedState from control file. If file doesn't exist, bails out.
    fn restore(conf: &SafeKeeperConf, ttid: &TenantTimelineId) -> Result<Self> {
        let control_store = control_file::FileStorage::restore_new(ttid, conf)?;
        if control_store.server.wal_seg_size == 0 {
            bail!(TimelineError::UninitializedWalSegSize(*ttid));
        }

        let wal_store =
            wal_storage::PhysicalStorage::new(ttid, conf.timeline_dir(ttid), conf, &control_store)?;

        Ok(Self {
            sk: SafeKeeper::new(control_store, wal_store, conf.my_id)?,
            peers_info: PeersInfo(vec![]),
            wal_backup_active: false,
            active: false,
            num_computes: 0,
            last_removed_segno: 0,
        })
    }

    fn is_active(&self, remote_consistent_lsn: Lsn) -> bool {
        self.is_wal_backup_required()
            // FIXME: add tracking of relevant pageservers and check them here individually,
            // otherwise migration won't work (we suspend too early).
            || remote_consistent_lsn < self.sk.inmem.commit_lsn
    }

    /// Mark timeline active/inactive and return whether s3 offloading requires
    /// start/stop action.
    fn update_status(&mut self, remote_consistent_lsn: Lsn, ttid: TenantTimelineId) -> bool {
        let is_active = self.is_active(remote_consistent_lsn);
        if self.active != is_active {
            info!("timeline {} active={} now", ttid, is_active);
        }
        self.active = is_active;
        self.is_wal_backup_action_pending()
    }

    /// Should we run s3 offloading in current state?
    fn is_wal_backup_required(&self) -> bool {
        let seg_size = self.get_wal_seg_size();
        self.num_computes > 0 ||
        // Currently only the whole segment is offloaded, so compare segment numbers.
               (self.sk.inmem.commit_lsn.segment_number(seg_size) >
                self.sk.inmem.backup_lsn.segment_number(seg_size))
    }

    /// Is current state of s3 offloading is not what it ought to be?
    fn is_wal_backup_action_pending(&self) -> bool {
        let res = self.wal_backup_active != self.is_wal_backup_required();
        if res {
            let action_pending = if self.is_wal_backup_required() {
                "start"
            } else {
                "stop"
            };
            trace!(
                "timeline {} s3 offloading action {} pending: num_computes={}, commit_lsn={}, backup_lsn={}",
                self.sk.state.timeline_id, action_pending, self.num_computes, self.sk.inmem.commit_lsn, self.sk.inmem.backup_lsn
            );
        }
        res
    }

    /// Returns whether s3 offloading is required and sets current status as
    /// matching.
    fn wal_backup_attend(&mut self) -> bool {
        self.wal_backup_active = self.is_wal_backup_required();
        self.wal_backup_active
    }

    fn get_wal_seg_size(&self) -> usize {
        self.sk.state.server.wal_seg_size as usize
    }

    fn get_safekeeper_info(
        &self,
        ttid: &TenantTimelineId,
        conf: &SafeKeeperConf,
        remote_consistent_lsn: Lsn,
    ) -> SafekeeperTimelineInfo {
        SafekeeperTimelineInfo {
            safekeeper_id: conf.my_id.0,
            tenant_timeline_id: Some(ProtoTenantTimelineId {
                tenant_id: ttid.tenant_id.as_ref().to_owned(),
                timeline_id: ttid.timeline_id.as_ref().to_owned(),
            }),
            last_log_term: self.sk.get_epoch(),
            flush_lsn: self.sk.wal_store.flush_lsn().0,
            // note: this value is not flushed to control file yet and can be lost
            commit_lsn: self.sk.inmem.commit_lsn.0,
            // TODO: rework feedbacks to avoid max here
            remote_consistent_lsn: remote_consistent_lsn.0,
            peer_horizon_lsn: self.sk.inmem.peer_horizon_lsn.0,
            safekeeper_connstr: conf.listen_pg_addr.clone(),
            backup_lsn: self.sk.inmem.backup_lsn.0,
            local_start_lsn: self.sk.state.local_start_lsn.0,
            availability_zone: conf.availability_zone.clone(),
        }
    }
}

#[derive(Debug, thiserror::Error)]
pub enum TimelineError {
    #[error("Timeline {0} was cancelled and cannot be used anymore")]
    Cancelled(TenantTimelineId),
    #[error("Timeline {0} was not found in global map")]
    NotFound(TenantTimelineId),
    #[error("Timeline {0} exists on disk, but wasn't loaded on startup")]
    Invalid(TenantTimelineId),
    #[error("Timeline {0} is already exists")]
    AlreadyExists(TenantTimelineId),
    #[error("Timeline {0} is not initialized, wal_seg_size is zero")]
    UninitializedWalSegSize(TenantTimelineId),
    #[error("Timeline {0} is not initialized, pg_version is unknown")]
    UninitialinzedPgVersion(TenantTimelineId),
}

// Convert to HTTP API error.
impl From<TimelineError> for ApiError {
    fn from(te: TimelineError) -> ApiError {
        match te {
            TimelineError::NotFound(ttid) => {
                ApiError::NotFound(anyhow!("timeline {} not found", ttid))
            }
            _ => ApiError::InternalServerError(anyhow!("{}", te)),
        }
    }
}

/// Timeline struct manages lifecycle (creation, deletion, restore) of a safekeeper timeline.
/// It also holds SharedState and provides mutually exclusive access to it.
pub struct Timeline {
    pub ttid: TenantTimelineId,

    /// Sending here asks for wal backup launcher attention (start/stop
    /// offloading). Sending ttid instead of concrete command allows to do
    /// sending without timeline lock.
    pub wal_backup_launcher_tx: Sender<TenantTimelineId>,

    /// Used to broadcast commit_lsn updates to all background jobs.
    commit_lsn_watch_tx: watch::Sender<Lsn>,
    commit_lsn_watch_rx: watch::Receiver<Lsn>,

    /// Safekeeper and other state, that should remain consistent and synchronized
    /// with the disk.
    mutex: Mutex<SharedState>,
    walsenders: Arc<WalSenders>,

    /// Cancellation channel. Delete/cancel will send `true` here as a cancellation signal.
    cancellation_tx: watch::Sender<bool>,

    /// Timeline should not be used after cancellation. Background tasks should
    /// monitor this channel and stop eventually after receiving `true` from this channel.
    cancellation_rx: watch::Receiver<bool>,

    /// Directory where timeline state is stored.
    pub timeline_dir: PathBuf,
}

impl Timeline {
    /// Load existing timeline from disk.
    pub fn load_timeline(
        conf: SafeKeeperConf,
        ttid: TenantTimelineId,
        wal_backup_launcher_tx: Sender<TenantTimelineId>,
    ) -> Result<Timeline> {
        let _enter = info_span!("load_timeline", timeline = %ttid.timeline_id).entered();

        let shared_state = SharedState::restore(&conf, &ttid)?;
        let rcl = shared_state.sk.state.remote_consistent_lsn;
        let (commit_lsn_watch_tx, commit_lsn_watch_rx) =
            watch::channel(shared_state.sk.state.commit_lsn);
        let (cancellation_tx, cancellation_rx) = watch::channel(false);

        Ok(Timeline {
            ttid,
            wal_backup_launcher_tx,
            commit_lsn_watch_tx,
            commit_lsn_watch_rx,
            mutex: Mutex::new(shared_state),
            walsenders: WalSenders::new(rcl),
            cancellation_rx,
            cancellation_tx,
            timeline_dir: conf.timeline_dir(&ttid),
        })
    }

    /// Create a new timeline, which is not yet persisted to disk.
    pub fn create_empty(
        conf: SafeKeeperConf,
        ttid: TenantTimelineId,
        wal_backup_launcher_tx: Sender<TenantTimelineId>,
        server_info: ServerInfo,
        commit_lsn: Lsn,
        local_start_lsn: Lsn,
    ) -> Result<Timeline> {
        let (commit_lsn_watch_tx, commit_lsn_watch_rx) = watch::channel(Lsn::INVALID);
        let (cancellation_tx, cancellation_rx) = watch::channel(false);
        let state = SafeKeeperState::new(&ttid, server_info, vec![], commit_lsn, local_start_lsn);

        Ok(Timeline {
            ttid,
            wal_backup_launcher_tx,
            commit_lsn_watch_tx,
            commit_lsn_watch_rx,
            mutex: Mutex::new(SharedState::create_new(&conf, &ttid, state)?),
            walsenders: WalSenders::new(Lsn(0)),
            cancellation_rx,
            cancellation_tx,
            timeline_dir: conf.timeline_dir(&ttid),
        })
    }

    /// Initialize fresh timeline on disk and start background tasks. If bootstrap
    /// fails, timeline is cancelled and cannot be used anymore.
    ///
    /// Bootstrap is transactional, so if it fails, created files will be deleted,
    /// and state on disk should remain unchanged.
    pub fn bootstrap(&self, shared_state: &mut MutexGuard<SharedState>) -> Result<()> {
        match std::fs::metadata(&self.timeline_dir) {
            Ok(_) => {
                // Timeline directory exists on disk, we should leave state unchanged
                // and return error.
                bail!(TimelineError::Invalid(self.ttid));
            }
            Err(e) if e.kind() == std::io::ErrorKind::NotFound => {}
            Err(e) => {
                return Err(e.into());
            }
        }

        // Create timeline directory.
        std::fs::create_dir_all(&self.timeline_dir)?;

        // Write timeline to disk and TODO: start background tasks.
        match || -> Result<()> {
            shared_state.sk.persist()?;
            // TODO: add more initialization steps here
            self.update_status(shared_state);
            Ok(())
        }() {
            Ok(_) => Ok(()),
            Err(e) => {
                // Bootstrap failed, cancel timeline and remove timeline directory.
                self.cancel(shared_state);

                if let Err(fs_err) = std::fs::remove_dir_all(&self.timeline_dir) {
                    warn!(
                        "failed to remove timeline {} directory after bootstrap failure: {}",
                        self.ttid, fs_err
                    );
                }

                Err(e)
            }
        }
    }

    /// Delete timeline from disk completely, by removing timeline directory. Background
    /// timeline activities will stop eventually.
    pub fn delete_from_disk(
        &self,
        shared_state: &mut MutexGuard<SharedState>,
    ) -> Result<(bool, bool)> {
        let was_active = shared_state.active;
        self.cancel(shared_state);
        let dir_existed = delete_dir(&self.timeline_dir)?;
        Ok((dir_existed, was_active))
    }

    /// Cancel timeline to prevent further usage. Background tasks will stop
    /// eventually after receiving cancellation signal.
    fn cancel(&self, shared_state: &mut MutexGuard<SharedState>) {
        info!("timeline {} is cancelled", self.ttid);
        let _ = self.cancellation_tx.send(true);
        let res = self.wal_backup_launcher_tx.blocking_send(self.ttid);
        if let Err(e) = res {
            error!("Failed to send stop signal to wal_backup_launcher: {}", e);
        }
        // Close associated FDs. Nobody will be able to touch timeline data once
        // it is cancelled, so WAL storage won't be opened again.
        shared_state.sk.wal_store.close();
    }

    /// Returns if timeline is cancelled.
    pub fn is_cancelled(&self) -> bool {
        *self.cancellation_rx.borrow()
    }

    /// Take a writing mutual exclusive lock on timeline shared_state.
    pub fn write_shared_state(&self) -> MutexGuard<SharedState> {
        self.mutex.lock()
    }

    fn update_status(&self, shared_state: &mut SharedState) -> bool {
        shared_state.update_status(self.get_walsenders().get_remote_consistent_lsn(), self.ttid)
    }

    /// Register compute connection, starting timeline-related activity if it is
    /// not running yet.
    pub async fn on_compute_connect(&self) -> Result<()> {
        if self.is_cancelled() {
            bail!(TimelineError::Cancelled(self.ttid));
        }

        let is_wal_backup_action_pending: bool;
        {
            let mut shared_state = self.write_shared_state();
            shared_state.num_computes += 1;
            is_wal_backup_action_pending = self.update_status(&mut shared_state);
        }
        // Wake up wal backup launcher, if offloading not started yet.
        if is_wal_backup_action_pending {
            // Can fail only if channel to a static thread got closed, which is not normal at all.
            self.wal_backup_launcher_tx.send(self.ttid).await?;
        }
        Ok(())
    }

    /// De-register compute connection, shutting down timeline activity if
    /// pageserver doesn't need catchup.
    pub fn on_compute_disconnect(&self) -> Result<()> {
        let is_wal_backup_action_pending: bool;
        {
            let mut shared_state = self.write_shared_state();
            shared_state.num_computes -= 1;
            is_wal_backup_action_pending = self.update_status(&mut shared_state);
        }
        // Wake up wal backup launcher, if it is time to stop the offloading.
        if is_wal_backup_action_pending {
            // Can fail only if channel to a static thread got closed, which is not normal at all.
            //
            // Note: this is blocking_send because on_compute_disconnect is called in Drop, there is
            // no async Drop and we use current thread runtimes. With current thread rt spawning
            // task in drop impl is racy, as thread along with runtime might finish before the task.
            // This should be switched send.await when/if we go to full async.
            self.wal_backup_launcher_tx.blocking_send(self.ttid)?;
        }
        Ok(())
    }

    /// Returns true if walsender should stop sending WAL to pageserver. We
    /// terminate it if remote_consistent_lsn reached commit_lsn and there is no
    /// computes. While there might be nothing to stream already, we learn about
    /// remote_consistent_lsn update through replication feedback, and we want
    /// to stop pushing to the broker if pageserver is fully caughtup.
    pub fn should_walsender_stop(&self, reported_remote_consistent_lsn: Lsn) -> bool {
        if self.is_cancelled() {
            return true;
        }
        let shared_state = self.write_shared_state();
        if shared_state.num_computes == 0 {
            return shared_state.sk.inmem.commit_lsn == Lsn(0) || // no data at all yet
            reported_remote_consistent_lsn >= shared_state.sk.inmem.commit_lsn;
        }
        false
    }

    /// Returns whether s3 offloading is required and sets current status as
    /// matching it.
    pub fn wal_backup_attend(&self) -> bool {
        if self.is_cancelled() {
            return false;
        }

        self.write_shared_state().wal_backup_attend()
    }

    /// Returns commit_lsn watch channel.
    pub fn get_commit_lsn_watch_rx(&self) -> watch::Receiver<Lsn> {
        self.commit_lsn_watch_rx.clone()
    }

    /// Pass arrived message to the safekeeper.
    pub fn process_msg(
        &self,
        msg: &ProposerAcceptorMessage,
    ) -> Result<Option<AcceptorProposerMessage>> {
        if self.is_cancelled() {
            bail!(TimelineError::Cancelled(self.ttid));
        }

        let mut rmsg: Option<AcceptorProposerMessage>;
        let commit_lsn: Lsn;
        {
            let mut shared_state = self.write_shared_state();
            rmsg = shared_state.sk.process_msg(msg)?;

            // if this is AppendResponse, fill in proper pageserver and hot
            // standby feedback.
            if let Some(AcceptorProposerMessage::AppendResponse(ref mut resp)) = rmsg {
                let (ps_feedback, hs_feedback) = self.walsenders.get_feedbacks();
                resp.hs_feedback = hs_feedback;
                resp.pageserver_feedback = ps_feedback;
            }

            commit_lsn = shared_state.sk.inmem.commit_lsn;
        }
        self.commit_lsn_watch_tx.send(commit_lsn)?;
        Ok(rmsg)
    }

    /// Returns wal_seg_size.
    pub fn get_wal_seg_size(&self) -> usize {
        self.write_shared_state().get_wal_seg_size()
    }

    /// Returns true only if the timeline is loaded and active.
    pub fn is_active(&self) -> bool {
        if self.is_cancelled() {
            return false;
        }

        self.write_shared_state().active
    }

    /// Returns state of the timeline.
    pub fn get_state(&self) -> (SafekeeperMemState, SafeKeeperState) {
        let state = self.write_shared_state();
        (state.sk.inmem.clone(), state.sk.state.clone())
    }

    /// Returns latest backup_lsn.
    pub fn get_wal_backup_lsn(&self) -> Lsn {
        self.write_shared_state().sk.inmem.backup_lsn
    }

    /// Sets backup_lsn to the given value.
    pub fn set_wal_backup_lsn(&self, backup_lsn: Lsn) -> Result<()> {
        if self.is_cancelled() {
            bail!(TimelineError::Cancelled(self.ttid));
        }

        let mut state = self.write_shared_state();
        state.sk.inmem.backup_lsn = max(state.sk.inmem.backup_lsn, backup_lsn);
        // we should check whether to shut down offloader, but this will be done
        // soon by peer communication anyway.
        Ok(())
    }

    /// Get safekeeper info for broadcasting to broker and other peers.
    pub fn get_safekeeper_info(&self, conf: &SafeKeeperConf) -> SafekeeperTimelineInfo {
        let shared_state = self.write_shared_state();
        shared_state.get_safekeeper_info(
            &self.ttid,
            conf,
            self.walsenders.get_remote_consistent_lsn(),
        )
    }

    /// Update timeline state with peer safekeeper data.
    pub async fn record_safekeeper_info(&self, mut sk_info: SafekeeperTimelineInfo) -> Result<()> {
        // Update local remote_consistent_lsn in memory (in .walsenders) and in
        // sk_info to pass it down to control file.
        sk_info.remote_consistent_lsn = self
            .walsenders
            .update_remote_consistent_lsn(Lsn(sk_info.remote_consistent_lsn))
            .0;
        let is_wal_backup_action_pending: bool;
        let commit_lsn: Lsn;
        {
            let mut shared_state = self.write_shared_state();
            shared_state.sk.record_safekeeper_info(&sk_info)?;
            let peer_info = PeerInfo::from_sk_info(&sk_info, Instant::now());
            shared_state.peers_info.upsert(&peer_info);
            is_wal_backup_action_pending = self.update_status(&mut shared_state);
            commit_lsn = shared_state.sk.inmem.commit_lsn;
        }
        self.commit_lsn_watch_tx.send(commit_lsn)?;
        // Wake up wal backup launcher, if it is time to stop the offloading.
        if is_wal_backup_action_pending {
            self.wal_backup_launcher_tx.send(self.ttid).await?;
        }
        Ok(())
    }

    /// Get our latest view of alive peers status on the timeline.
    /// We pass our own info through the broker as well, so when we don't have connection
    /// to the broker returned vec is empty.
    pub fn get_peers(&self, conf: &SafeKeeperConf) -> Vec<PeerInfo> {
        let shared_state = self.write_shared_state();
        let now = Instant::now();
        shared_state
            .peers_info
            .0
            .iter()
            // Regard peer as absent if we haven't heard from it within heartbeat_timeout.
            .filter(|p| now.duration_since(p.ts) <= conf.heartbeat_timeout)
            .cloned()
            .collect()
    }

    pub fn get_walsenders(&self) -> &Arc<WalSenders> {
        &self.walsenders
    }

    /// Returns flush_lsn.
    pub fn get_flush_lsn(&self) -> Lsn {
        self.write_shared_state().sk.wal_store.flush_lsn()
    }

    /// Delete WAL segments from disk that are no longer needed. This is determined
    /// based on pageserver's remote_consistent_lsn and local backup_lsn/peer_lsn.
    pub fn remove_old_wal(&self, wal_backup_enabled: bool) -> Result<()> {
        if self.is_cancelled() {
            bail!(TimelineError::Cancelled(self.ttid));
        }

        let horizon_segno: XLogSegNo;
        let remover: Box<dyn Fn(u64) -> Result<(), anyhow::Error>>;
        {
            let shared_state = self.write_shared_state();
            horizon_segno = shared_state.sk.get_horizon_segno(wal_backup_enabled);
            remover = shared_state.sk.wal_store.remove_up_to();
            if horizon_segno <= 1 || horizon_segno <= shared_state.last_removed_segno {
                return Ok(());
            }
            // release the lock before removing
        }

        // delete old WAL files
        remover(horizon_segno - 1)?;

        // update last_removed_segno
        let mut shared_state = self.write_shared_state();
        shared_state.last_removed_segno = horizon_segno;
        Ok(())
    }

    /// Returns full timeline info, required for the metrics. If the timeline is
    /// not active, returns None instead.
    pub fn info_for_metrics(&self) -> Option<FullTimelineInfo> {
        if self.is_cancelled() {
            return None;
        }

        let ps_feedback = self.walsenders.get_ps_feedback();
        let state = self.write_shared_state();
        if state.active {
            Some(FullTimelineInfo {
                ttid: self.ttid,
                ps_feedback,
                wal_backup_active: state.wal_backup_active,
                timeline_is_active: state.active,
                num_computes: state.num_computes,
                last_removed_segno: state.last_removed_segno,
                epoch_start_lsn: state.sk.epoch_start_lsn,
                mem_state: state.sk.inmem.clone(),
                persisted_state: state.sk.state.clone(),
                flush_lsn: state.sk.wal_store.flush_lsn(),
                remote_consistent_lsn: self.get_walsenders().get_remote_consistent_lsn(),
                wal_storage: state.sk.wal_store.get_metrics(),
            })
        } else {
            None
        }
    }

    /// Returns in-memory timeline state to build a full debug dump.
    pub fn memory_dump(&self) -> debug_dump::Memory {
        let state = self.write_shared_state();

        let (write_lsn, write_record_lsn, flush_lsn, file_open) =
            state.sk.wal_store.internal_state();

        debug_dump::Memory {
            is_cancelled: self.is_cancelled(),
            peers_info_len: state.peers_info.0.len(),
            walsenders: self.walsenders.get_all(),
            wal_backup_active: state.wal_backup_active,
            active: state.active,
            num_computes: state.num_computes,
            last_removed_segno: state.last_removed_segno,
            epoch_start_lsn: state.sk.epoch_start_lsn,
            mem_state: state.sk.inmem.clone(),
            write_lsn,
            write_record_lsn,
            flush_lsn,
            file_open,
        }
    }
}

/// Deletes directory and it's contents. Returns false if directory does not exist.
fn delete_dir(path: &PathBuf) -> Result<bool> {
    match std::fs::remove_dir_all(path) {
        Ok(_) => Ok(true),
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(false),
        Err(e) => Err(e.into()),
    }
}