diff --git a/archapp/src/archeng.rs b/archapp/src/archeng.rs
index 72c9c45..7c526fa 100644
--- a/archapp/src/archeng.rs
+++ b/archapp/src/archeng.rs
@@ -1,10 +1,13 @@
+pub mod backreadbuf;
 pub mod blockstream;
+pub mod bufminread;
 pub mod datablock;
 pub mod datablockstream;
 pub mod diskio;
 pub mod indexfiles;
 pub mod indextree;
 pub mod pipe;
+pub mod ringbuf;
 
 use self::indexfiles::list_index_files;
 use self::indextree::channel_list;
@@ -196,80 +199,6 @@ pub fn name_hash(s: &str, ht_len: u32) -> u32 {
     h
 }
 
-pub struct RingBuf {
-    buf: Vec<u8>,
-    wp: usize,
-    rp: usize,
-}
-
-impl RingBuf {
-    pub fn new() -> Self {
-        Self {
-            buf: vec![0; 1024 * 8],
-            wp: 0,
-            rp: 0,
-        }
-    }
-
-    pub fn reset(&mut self) {
-        self.rp = 0;
-        self.wp = 0;
-    }
-
-    pub fn len(&self) -> usize {
-        self.wp - self.rp
-    }
-
-    pub fn adv(&mut self, n: usize) {
-        self.rp += n;
-    }
-
-    pub fn data(&self) -> &[u8] {
-        &self.buf[self.rp..self.wp]
-    }
-
-    pub async fn fill(&mut self, file: &mut File, stats: &StatsChannel) -> Result<usize, Error> {
-        if self.rp == self.wp {
-            if self.rp != 0 {
-                self.wp = 0;
-                self.rp = 0;
-            }
-        } else {
-            unsafe {
-                std::ptr::copy::<u8>(&self.buf[self.rp], &mut self.buf[0], self.len());
-                self.wp -= self.rp;
-                self.rp = 0;
-            }
-        }
-        let n = read(file, &mut self.buf[self.wp..], stats).await?;
-        self.wp += n;
-        return Ok(n);
-    }
-
-    pub async fn fill_if_low(&mut self, file: &mut File, stats: &StatsChannel) -> Result<usize, Error> {
-        let len = self.len();
-        let cap = self.buf.len();
-        while self.len() < cap / 6 {
-            let n = self.fill(file, stats).await?;
-            if n == 0 {
-                break;
-            }
-        }
-        return Ok(self.len() - len);
-    }
-
-    pub async fn fill_min(&mut self, file: &mut File, min: usize, stats: &StatsChannel) -> Result<usize, Error> {
-        let len = self.len();
-        while self.len() < min {
-            let n = self.fill(file, stats).await?;
-            if n == 0 {
-                return Err(Error::with_msg_no_trace(format!("fill_min can not read min {}", min)));
-            }
-        }
-        return Ok(self.len() - len);
-    }
-}
-
 fn format_hex_block(buf: &[u8], max: usize) -> String {
     use std::fmt::Write;
     const COLS: usize = 16;
diff --git a/archapp/src/archeng/backreadbuf.rs b/archapp/src/archeng/backreadbuf.rs
new file mode 100644
index 0000000..4c97709
--- /dev/null
+++ b/archapp/src/archeng/backreadbuf.rs
@@ -0,0 +1,118 @@
+use crate::archeng::{read, seek, StatsChannel};
+use err::Error;
+use netpod::log::*;
+use std::{borrow::BorrowMut, io::SeekFrom};
+use tokio::fs::File;
+
+pub struct BackReadBuf<F> {
+    file: F,
+    buf: Vec<u8>,
+    abs: u64,
+    wp: usize,
+    rp: usize,
+    stats: StatsChannel,
+    seek_request: u64,
+    seek_done: u64,
+    read_done: u64,
+}
+
+impl<F> BackReadBuf<F>
+where
+    F: BorrowMut<File>,
+{
+    pub async fn new(file: F, pos: u64, stats: StatsChannel) -> Result<Self, Error> {
+        let mut ret = Self {
+            file,
+            buf: vec![0; 1024 * 8],
+            abs: pos,
+            wp: 0,
+            rp: 0,
+            stats,
+            seek_request: 0,
+            seek_done: 0,
+            read_done: 0,
+        };
+        ret.seek(pos).await?;
+        Ok(ret)
+    }
+
+    pub fn into_file(self) -> F {
+        //self.file
+        err::todoval()
+    }
+
+    pub fn len(&self) -> usize {
+        self.wp - self.rp
+    }
+
+    pub fn adv(&mut self, n: usize) {
+        self.rp += n;
+    }
+
+    pub fn data(&self) -> &[u8] {
+        &self.buf[self.rp..self.wp]
+    }
+
+    async fn fill(&mut self) -> Result<usize, Error> {
+        if self.rp != 0 && self.rp == self.wp {
+            self.wp = 0;
+            self.rp = 0;
+        } else {
+            unsafe {
+                std::ptr::copy::<u8>(&self.buf[self.rp], &mut self.buf[0], self.len());
+                self.wp -= self.rp;
+                self.rp = 0;
+            }
+        }
+        let n = read(&mut self.file.borrow_mut(), &mut self.buf[self.wp..], &self.stats).await?;
+        //debug!("I/O fill  n {}", n);
+        self.wp += n;
+        self.read_done += 1;
+        Ok(n)
+    }
+
+    pub async fn fill_min(&mut self, min: usize) -> Result<usize, Error> {
+        let len = self.len();
+        while self.len() < min {
+            let n = self.fill().await?;
+            if n == 0 {
+                return Err(Error::with_msg_no_trace(format!("fill_min can not read min {}", min)));
+            }
+        }
+        Ok(self.len() - len)
+    }
+
+    pub async fn seek(&mut self, pos: u64) -> Result<u64, Error> {
+        let dp = pos as i64 - self.abs as i64 - self.rp as i64;
+        if pos >= self.abs && pos < self.abs + self.buf.len() as u64 - 64 {
+            self.rp = (pos - self.abs) as usize;
+            self.seek_request += 1;
+            Ok(pos)
+        } else {
+            //debug!("I/O seek  dp {}", dp);
+            let s0 = pos.min(1024 * 2 - 256);
+            self.abs = pos - s0;
+            self.rp = 0;
+            self.wp = 0;
+            let ret = seek(self.file.borrow_mut(), SeekFrom::Start(self.abs), &self.stats)
+                .await
+                .map_err(|e| Error::from(e))?;
+            self.fill_min(s0 as usize).await?;
+            self.rp = s0 as usize;
+            self.seek_request += 1;
+            self.seek_done += 1;
+            Ok(ret)
+        }
+    }
+}
+
+impl<F> Drop for BackReadBuf<F> {
+    fn drop(&mut self) {
+        info!(
+            "BackReadBuf  Drop  {}  {}%  {}",
+            self.seek_request,
+            self.seek_done * 100 / self.seek_request,
+            self.read_done
+        );
+    }
+}
diff --git a/archapp/src/archeng/blockstream.rs b/archapp/src/archeng/blockstream.rs
index 6f75630..8daebc2 100644
--- a/archapp/src/archeng/blockstream.rs
+++ b/archapp/src/archeng/blockstream.rs
@@ -1,9 +1,14 @@
-use crate::archeng::datablock::{read_data_1, read_datafile_header};
+use crate::archeng::backreadbuf::BackReadBuf;
+use crate::archeng::datablock::{read_data2, read_data_1, read_datafile_header, read_datafile_header2};
 use crate::archeng::indexfiles::{database_connect, unfold_stream, UnfoldExec};
-use crate::archeng::indextree::{read_datablockref, IndexFileBasics, RecordIter, RecordTarget};
+use crate::archeng::indextree::{
+    read_datablockref, read_datablockref2, DataheaderPos, HeaderVersion, IndexFileBasics, RecordIter, RecordTarget,
+};
+use crate::archeng::ringbuf::RingBuf;
 use crate::archeng::{open_read, seek, StatsChannel};
 use err::Error;
 use futures_core::{Future, Stream};
+use items::WithLen;
 #[allow(unused)]
 use netpod::log::*;
 use netpod::{Channel, ChannelArchiver, FilePos, NanoRange};
@@ -14,8 +19,6 @@ use std::path::PathBuf;
 use std::pin::Pin;
 use tokio::fs::File;
 
-use super::indextree::HeaderVersion;
-
 enum Steps {
     Start,
     SelectIndexFile,
@@ -30,12 +33,15 @@ struct DataBlocks {
     range: NanoRange,
     steps: Steps,
     paths: VecDeque<String>,
-    file1: Option<File>,
-    file2: Option<File>,
+    file1: Option<BackReadBuf<File>>,
+    file2: Option<RingBuf<File>>,
     last_dp: u64,
     last_dp2: u64,
     last_f2: String,
+    last_dfhpos: DataheaderPos,
     dfnotfound: BTreeMap<String, bool>,
+    data_bytes_read: u64,
+    same_dfh_count: u64,
 }
 
 impl DataBlocks {
@@ -51,7 +57,10 @@ impl DataBlocks {
             last_dp: 0,
             last_dp2: 0,
             last_f2: String::new(),
+            last_dfhpos: DataheaderPos(u64::MAX),
             dfnotfound: BTreeMap::new(),
+            data_bytes_read: 0,
+            same_dfh_count: 0,
         }
     }
 
@@ -77,14 +86,16 @@ impl DataBlocks {
                 // For simplicity, simply read all storage classes linearly.
                 if let Some(path) = self.paths.pop_front() {
                     // TODO
-                    let basics = IndexFileBasics::from_path(&path, stats).await?;
+                    let mut file = open_read(path.clone().into(), stats).await?;
+                    let basics = IndexFileBasics::from_file(&path, &mut file, stats).await?;
                     let mut tree = basics
                         .rtree_for_channel(self.channel.name(), stats)
                         .await?
                         .ok_or_else(|| Error::with_msg_no_trace("channel not in index files"))?;
                     if let Some(iter) = tree.iter_range(self.range.clone(), stats).await? {
+                        debug!("SetupNextPath {:?}", path);
                         self.steps = ReadBlocks(iter, basics.hver().duplicate(), path.clone().into());
-                        self.file1 = Some(open_read(path.into(), stats).await?);
+                        self.file1 = Some(BackReadBuf::new(file, 0, stats.clone()).await?);
                     } else {
                         self.steps = SetupNextPath;
                     };
@@ -101,43 +112,68 @@ impl DataBlocks {
                     // TODO the iterator should actually return Dataref. We never expect child nodes here.
                     if let RecordTarget::Dataref(dp) = rec.target {
                         let f1 = self.file1.as_mut().unwrap();
-                        //seek(f1, SeekFrom::Start(dp.0), stats).await?;
-                        // Read the dataheader...
-                        // TODO the function should take a DatarefPos or?
-                        // TODO the seek is hidden in the function which makes possible optimization not accessible.
-                        let dref = read_datablockref(f1, FilePos { pos: dp.0 }, hver.as_ref(), stats).await?;
+                        let dref = read_datablockref2(f1, dp.clone(), hver.as_ref()).await?;
                         // TODO Remember the index path, need it here for relative path.
                         // TODO open datafile, relative path to index path.
                         // TODO keep open when path does not change.
                         let acc;
                         let num_samples;
-                        if let Some(_) = self.dfnotfound.get(dref.file_name()) {
-                            num_samples = 0;
-                            acc = 1;
-                        } else {
-                            if dref.file_name() == self.last_f2 {
-                                acc = 2;
-                            } else {
-                                let dpath = indexpath.parent().unwrap().join(dref.file_name());
-                                match open_read(dpath, stats).await {
-                                    Ok(f2) => {
-                                        acc = 4;
-                                        self.file2 = Some(f2);
-                                        self.last_f2 = dref.file_name().into();
-                                    }
-                                    Err(_) => {
-                                        acc = 3;
-                                        self.file2 = None;
-                                    }
-                                }
-                            };
-                            if let Some(f2) = self.file2.as_mut() {
-                                let dfheader = read_datafile_header(f2, dref.data_header_pos(), stats).await?;
-                                num_samples = dfheader.num_samples;
-                            } else {
-                                self.dfnotfound.insert(dref.file_name().into(), true);
+                        if true {
+                            if let Some(_) = self.dfnotfound.get(dref.file_name()) {
                                 num_samples = 0;
-                            };
+                                acc = 1;
+                            } else {
+                                if dref.file_name() == self.last_f2 {
+                                    acc = 2;
+                                } else {
+                                    let dpath = indexpath.parent().unwrap().join(dref.file_name());
+                                    match open_read(dpath, stats).await {
+                                        Ok(f2) => {
+                                            acc = 4;
+                                            self.file2 = Some(
+                                                RingBuf::new(f2, dref.data_header_pos().0, StatsChannel::dummy())
+                                                    .await?,
+                                            );
+                                            self.last_f2 = dref.file_name().into();
+                                        }
+                                        Err(_) => {
+                                            acc = 3;
+                                            self.file2 = None;
+                                        }
+                                    }
+                                };
+                                if let Some(f2) = self.file2.as_mut() {
+                                    if dref.file_name() == self.last_f2 && dref.data_header_pos() == self.last_dfhpos {
+                                        num_samples = 0;
+                                    } else {
+                                        self.last_dfhpos = dref.data_header_pos();
+                                        let rp1 = f2.rp_abs();
+                                        let dfheader = read_datafile_header2(f2, dref.data_header_pos()).await?;
+                                        let data = read_data2(f2, &dfheader, self.range.clone(), false).await?;
+                                        let rp2 = f2.rp_abs();
+                                        self.data_bytes_read += rp2 - rp1;
+                                        num_samples = dfheader.num_samples;
+                                        if data.len() != num_samples as usize {
+                                            if (data.len() as i64 - num_samples as i64).abs() < 4 {
+                                                // TODO get always one event less than num_samples tells us.
+                                                //warn!("small deviation  {} vs {}", data.len(), num_samples);
+                                            } else {
+                                                return Err(Error::with_msg_no_trace(format!(
+                                                    "event count mismatch  {} vs {}",
+                                                    data.len(),
+                                                    num_samples
+                                                )));
+                                            }
+                                        }
+                                    }
+                                } else {
+                                    self.dfnotfound.insert(dref.file_name().into(), true);
+                                    num_samples = 0;
+                                };
+                            }
+                        } else {
+                            acc = 6;
+                            num_samples = 0;
                         }
                         let item = serde_json::to_value((
                             dp.0,
@@ -156,6 +192,10 @@ impl DataBlocks {
                         panic!();
                     }
                 } else {
+                    info!(
+                        "data_bytes_read: {}  same_dfh_count: {}",
+                        self.data_bytes_read, self.same_dfh_count
+                    );
                     self.steps = SetupNextPath;
                     JsVal::String(format!("NOMORE"))
                 };
diff --git a/archapp/src/archeng/bufminread.rs b/archapp/src/archeng/bufminread.rs
new file mode 100644
index 0000000..8b13789
--- /dev/null
+++ b/archapp/src/archeng/bufminread.rs
@@ -0,0 +1 @@
+
diff --git a/archapp/src/archeng/datablock.rs b/archapp/src/archeng/datablock.rs
index 6a4b317..4804bb7 100644
--- a/archapp/src/archeng/datablock.rs
+++ b/archapp/src/archeng/datablock.rs
@@ -1,6 +1,5 @@
-use crate::archeng::{
-    read_exact, read_string, readf64, readu16, readu32, seek, RingBuf, StatsChannel, EPICS_EPOCH_OFFSET,
-};
+use crate::archeng::ringbuf::RingBuf;
+use crate::archeng::{read_exact, read_string, readf64, readu16, readu32, seek, StatsChannel, EPICS_EPOCH_OFFSET};
 use crate::eventsitem::EventsItem;
 use crate::plainevents::{PlainEvents, ScalarPlainEvents};
 use err::Error;
@@ -76,14 +75,14 @@ pub struct DatafileHeader {
 
 const DATA_HEADER_LEN_ON_DISK: usize = 72 + 40 + 40;
 
+// TODO retire this version (better version reads from buffer)
 pub async fn read_datafile_header(
     file: &mut File,
     pos: DataheaderPos,
     stats: &StatsChannel,
 ) -> Result<DatafileHeader, Error> {
-    seek(file, SeekFrom::Start(pos.0), stats).await?;
-    let mut rb = RingBuf::new();
-    rb.fill_min(file, DATA_HEADER_LEN_ON_DISK, stats).await?;
+    let mut rb = RingBuf::new(file, pos.0, stats.clone()).await?;
+    rb.fill_min(DATA_HEADER_LEN_ON_DISK).await?;
     let buf = rb.data();
     let dir_offset = readu32(buf, 0);
     let next_offset = readu32(buf, 4);
@@ -142,6 +141,136 @@ pub async fn read_datafile_header(
     Ok(ret)
 }
 
+pub async fn read_datafile_header2(rb: &mut RingBuf<File>, pos: DataheaderPos) -> Result<DatafileHeader, Error> {
+    // TODO avoid the extra seek: make sure that RingBuf catches this. Profile..
+    rb.seek(pos.0).await?;
+    rb.fill_min(DATA_HEADER_LEN_ON_DISK).await?;
+    let buf = rb.data();
+    let dir_offset = readu32(buf, 0);
+    let next_offset = readu32(buf, 4);
+    let prev_offset = readu32(buf, 8);
+    let curr_offset = readu32(buf, 12);
+    let num_samples = readu32(buf, 16);
+    let ctrl_info_offset = readu32(buf, 20);
+    let buf_size = readu32(buf, 24);
+    let buf_free = readu32(buf, 28);
+    let dbr_type = DbrType::from_u16(readu16(buf, 32))?;
+    let dbr_count = readu16(buf, 34);
+    // 4 bytes padding.
+    let period = readf64(buf, 40);
+    let ts1a = readu32(buf, 48);
+    let ts1b = readu32(buf, 52);
+    let ts2a = readu32(buf, 56);
+    let ts2b = readu32(buf, 60);
+    let ts3a = readu32(buf, 64);
+    let ts3b = readu32(buf, 68);
+    let ts_beg = if ts1a != 0 || ts1b != 0 {
+        ts1a as u64 * SEC + ts1b as u64 + EPICS_EPOCH_OFFSET
+    } else {
+        0
+    };
+    let ts_end = if ts3a != 0 || ts3b != 0 {
+        ts3a as u64 * SEC + ts3b as u64 + EPICS_EPOCH_OFFSET
+    } else {
+        0
+    };
+    let ts_next_file = if ts2a != 0 || ts2b != 0 {
+        ts2a as u64 * SEC + ts2b as u64 + EPICS_EPOCH_OFFSET
+    } else {
+        0
+    };
+    let fname_prev = read_string(&buf[72..112])?;
+    let fname_next = read_string(&buf[112..152])?;
+    rb.adv(DATA_HEADER_LEN_ON_DISK);
+    let ret = DatafileHeader {
+        pos,
+        dir_offset,
+        next_offset,
+        prev_offset,
+        curr_offset,
+        num_samples,
+        ctrl_info_offset,
+        buf_size,
+        buf_free,
+        dbr_type,
+        dbr_count: dbr_count as usize,
+        period,
+        ts_beg: Nanos { ns: ts_beg },
+        ts_end: Nanos { ns: ts_end },
+        ts_next_file: Nanos { ns: ts_next_file },
+        fname_next,
+        fname_prev,
+    };
+    Ok(ret)
+}
+
+pub async fn read_data2(
+    rb: &mut RingBuf<File>,
+    datafile_header: &DatafileHeader,
+    range: NanoRange,
+    _expand: bool,
+) -> Result<EventsItem, Error> {
+    // TODO handle expand mode
+    //let dhpos = datafile_header.pos.0 + DATA_HEADER_LEN_ON_DISK as u64;
+    //seek(file, SeekFrom::Start(dhpos), stats).await?;
+    let res = match &datafile_header.dbr_type {
+        DbrType::DbrTimeDouble => {
+            if datafile_header.dbr_count == 1 {
+                trace!("~~~~~~~~~~~~~~~~~~~~~   read  scalar  DbrTimeDouble");
+                let mut evs = EventValues {
+                    tss: vec![],
+                    values: vec![],
+                };
+                let n1 = datafile_header.num_samples as usize;
+                //let n2 = datafile_header.dbr_type.byte_len();
+                let n2 = 2 + 2 + 4 + 4 + (4) + 8;
+                let n3 = n1 * n2;
+                rb.fill_min(n3).await?;
+                //let mut buf = vec![0; n3];
+                //read_exact(file, &mut buf, stats).await?;
+                let buf = rb.data();
+                let mut p1 = 0;
+                let mut ntot = 0;
+                while p1 < n3 - n2 {
+                    let _status = u16::from_be_bytes(buf[p1..p1 + 2].try_into().unwrap());
+                    p1 += 2;
+                    let _severity = u16::from_be_bytes(buf[p1..p1 + 2].try_into().unwrap());
+                    p1 += 2;
+                    let ts1a = u32::from_be_bytes(buf[p1..p1 + 4].try_into().unwrap());
+                    p1 += 4;
+                    let ts1b = u32::from_be_bytes(buf[p1..p1 + 4].try_into().unwrap());
+                    p1 += 4;
+                    let ts1 = ts1a as u64 * SEC + ts1b as u64 + EPICS_EPOCH_OFFSET;
+                    p1 += 4;
+                    let value = f64::from_be_bytes(buf[p1..p1 + 8].try_into().unwrap());
+                    p1 += 8;
+                    ntot += 1;
+                    if ts1 >= range.beg && ts1 < range.end {
+                        evs.tss.push(ts1);
+                        evs.values.push(value);
+                    }
+                }
+                rb.adv(n3);
+                info!("parsed block with {} / {} events", ntot, evs.tss.len());
+                let evs = ScalarPlainEvents::Double(evs);
+                let plain = PlainEvents::Scalar(evs);
+                let item = EventsItem::Plain(plain);
+                item
+            } else {
+                let msg = format!("dbr_count {:?} not yet supported", datafile_header.dbr_count);
+                error!("{}", msg);
+                return Err(Error::with_msg_no_trace(msg));
+            }
+        }
+        _ => {
+            let msg = format!("Type {:?} not yet supported", datafile_header.dbr_type);
+            error!("{}", msg);
+            return Err(Error::with_msg_no_trace(msg));
+        }
+    };
+    Ok(res)
+}
+
 pub async fn read_data_1(
     file: &mut File,
     datafile_header: &DatafileHeader,
diff --git a/archapp/src/archeng/indexfiles.rs b/archapp/src/archeng/indexfiles.rs
index 43be010..1fbbce5 100644
--- a/archapp/src/archeng/indexfiles.rs
+++ b/archapp/src/archeng/indexfiles.rs
@@ -333,8 +333,9 @@ impl ScanChannels {
                         .await?;
                     if rows.len() == 1 {
                         let indexfile_rid: i64 = rows[0].try_get(0)?;
-                        let mut basics = super::indextree::IndexFileBasics::from_path(path, stats).await?;
-                        let entries = basics.all_channel_entries(stats).await?;
+                        let mut file = open_read(path.clone().into(), stats).await?;
+                        let mut basics = super::indextree::IndexFileBasics::from_file(path, &mut file, stats).await?;
+                        let entries = basics.all_channel_entries(&mut file, stats).await?;
                         for entry in entries {
                             let rows = dbc
                                 .query("select rowid from channels where name = $1", &[&entry.channel_name()])
diff --git a/archapp/src/archeng/indextree.rs b/archapp/src/archeng/indextree.rs
index b9868c3..86207f0 100644
--- a/archapp/src/archeng/indextree.rs
+++ b/archapp/src/archeng/indextree.rs
@@ -1,5 +1,6 @@
+use crate::archeng::ringbuf::RingBuf;
 use crate::archeng::{
-    format_hex_block, name_hash, open_read, readu16, readu32, readu64, seek, RingBuf, StatsChannel, EPICS_EPOCH_OFFSET,
+    format_hex_block, name_hash, open_read, readu16, readu32, readu64, seek, StatsChannel, EPICS_EPOCH_OFFSET,
 };
 use err::Error;
 use netpod::{log::*, NanoRange};
@@ -11,6 +12,8 @@ use std::path::{Path, PathBuf};
 use std::time::{Duration, Instant};
 use tokio::fs::File;
 
+use super::backreadbuf::BackReadBuf;
+
 pub trait HeaderVersion: Send + Sync + fmt::Debug {
     fn version(&self) -> u8;
     fn read_offset(&self, buf: &[u8], pos: usize) -> u64;
@@ -81,7 +84,6 @@ impl NamedHashChannelEntry {
 
 #[derive(Debug)]
 pub struct IndexFileBasics {
-    file: File,
     path: PathBuf,
     version: u8,
     name_hash_anchor_beg: u64,
@@ -100,21 +102,78 @@ pub struct IndexFileBasics {
 }
 
 impl IndexFileBasics {
-    pub async fn from_path(path: impl Into<PathBuf>, stats: &StatsChannel) -> Result<Self, Error> {
+    pub async fn from_file(path: impl Into<PathBuf>, file: &mut File, stats: &StatsChannel) -> Result<Self, Error> {
         let path = path.into();
-        let file = open_read(path.clone(), stats).await?;
         read_file_basics(path, file, stats).await
     }
 
     pub fn hver(&self) -> &Box<dyn HeaderVersion> {
         &self.hver
     }
+
+    pub async fn all_channel_entries(
+        &mut self,
+        file: &mut File,
+        stats: &StatsChannel,
+    ) -> Result<Vec<NamedHashChannelEntry>, Error> {
+        let mut entries = vec![];
+        let mut rb = RingBuf::new(file, 0, stats.clone()).await?;
+        for epos in &self.name_hash_entries {
+            if epos.named_hash_channel_entry_pos != 0 {
+                let mut pos = epos.named_hash_channel_entry_pos;
+                while pos != 0 {
+                    rb.seek(pos).await?;
+                    let min0 = 4 + 2 * self.hver.offset_size();
+                    rb.fill_min(min0).await?;
+                    let buf = rb.data();
+                    let entry = parse_name_hash_channel_entry(buf, self.hver.as_ref())?;
+                    info!("parsed entry {:?}", entry);
+                    pos = entry.next;
+                    entries.push(entry);
+                }
+            }
+        }
+        Ok(entries)
+    }
+
+    pub async fn rtree_for_channel(&self, channel_name: &str, stats: &StatsChannel) -> Result<Option<Rtree>, Error> {
+        // TODO in the common case, the caller has already a opened file and could reuse that here.
+        let mut index_file = open_read(self.path.clone(), stats).await?;
+        let chn_hash = name_hash(channel_name, self.name_hash_anchor_len as u32);
+        let epos = &self.name_hash_entries[chn_hash as usize];
+        let mut pos = epos.named_hash_channel_entry_pos;
+        if pos == 0 {
+            warn!("no hash entry for channel {}", channel_name);
+        }
+        let mut entries = vec![];
+        let mut rb = RingBuf::new(&mut index_file, pos, stats.clone()).await?;
+        while pos != 0 {
+            rb.seek(pos).await?;
+            let min0 = 4 + 2 * self.hver.offset_size();
+            rb.fill_min(min0).await?;
+            let buf = rb.data();
+            let e = parse_name_hash_channel_entry(buf, self.hver.as_ref())?;
+            let next = e.next;
+            entries.push(e);
+            pos = next;
+        }
+        drop(rb);
+        for e in &entries {
+            if e.channel_name == channel_name {
+                let hver = self.hver.duplicate();
+                let pos = RtreePos(e.id_rtree_pos);
+                // TODO Rtree could reuse the File here:
+                let tree = Rtree::new(self.path.clone(), index_file, pos, hver, stats).await?;
+                return Ok(Some(tree));
+            }
+        }
+        Ok(None)
+    }
 }
 
-pub async fn read_file_basics(path: PathBuf, file: File, stats: &StatsChannel) -> Result<IndexFileBasics, Error> {
-    let mut file = file;
-    let mut rb = RingBuf::new();
-    rb.fill_min(&mut file, 4, stats).await?;
+pub async fn read_file_basics(path: PathBuf, file: &mut File, stats: &StatsChannel) -> Result<IndexFileBasics, Error> {
+    let mut rb = RingBuf::new(file, 0, stats.clone()).await?;
+    rb.fill_min(4).await?;
     let buf = rb.data();
     let version = String::from_utf8(buf[3..4].to_vec())?.parse()?;
     let min0;
@@ -125,11 +184,10 @@ pub async fn read_file_basics(path: PathBuf, file: File, stats: &StatsChannel) -
     } else {
         panic!();
     }
-    rb.fill_min(&mut file, min0, stats).await?;
+    rb.fill_min(min0).await?;
     let buf = rb.data();
     let mut ret = if version == 3 {
         IndexFileBasics {
-            file,
             path,
             version,
             name_hash_anchor_beg: readu64(buf, 4),
@@ -148,7 +206,6 @@ pub async fn read_file_basics(path: PathBuf, file: File, stats: &StatsChannel) -
         }
     } else if version == 2 {
         IndexFileBasics {
-            file,
             path,
             version,
             name_hash_anchor_beg: readu32(buf, 4) as u64,
@@ -178,7 +235,7 @@ pub async fn read_file_basics(path: PathBuf, file: File, stats: &StatsChannel) -
     {
         let hver = &ret.hver;
         for _ in 0..ret.name_hash_anchor_len {
-            rb.fill_min(&mut ret.file, hver.offset_size(), stats).await?;
+            rb.fill_min(hver.offset_size()).await?;
             let buf = rb.data();
             let pos = hver.read_offset(buf, 0);
             rb.adv(hver.offset_size());
@@ -191,63 +248,6 @@ pub async fn read_file_basics(path: PathBuf, file: File, stats: &StatsChannel) -
     Ok(ret)
 }
 
-impl IndexFileBasics {
-    pub async fn all_channel_entries(&mut self, stats: &StatsChannel) -> Result<Vec<NamedHashChannelEntry>, Error> {
-        let mut entries = vec![];
-        let mut rb = RingBuf::new();
-        for epos in &self.name_hash_entries {
-            if epos.named_hash_channel_entry_pos != 0 {
-                let mut pos = epos.named_hash_channel_entry_pos;
-                while pos != 0 {
-                    rb.reset();
-                    seek(&mut self.file, SeekFrom::Start(pos), stats).await?;
-                    let min0 = 4 + 2 * self.hver.offset_size();
-                    rb.fill_min(&mut self.file, min0, stats).await?;
-                    let buf = rb.data();
-                    let entry = parse_name_hash_channel_entry(buf, self.hver.as_ref())?;
-                    info!("parsed entry {:?}", entry);
-                    pos = entry.next;
-                    entries.push(entry);
-                }
-            }
-        }
-        Ok(entries)
-    }
-
-    pub async fn rtree_for_channel(&self, channel_name: &str, stats: &StatsChannel) -> Result<Option<Rtree>, Error> {
-        let mut index_file = open_read(self.path.clone(), stats).await?;
-        let chn_hash = name_hash(channel_name, self.name_hash_anchor_len as u32);
-        let epos = &self.name_hash_entries[chn_hash as usize];
-        let mut pos = epos.named_hash_channel_entry_pos;
-        if pos == 0 {
-            warn!("no hash entry for channel {}", channel_name);
-        }
-        let mut entries = vec![];
-        let mut rb = RingBuf::new();
-        while pos != 0 {
-            rb.reset();
-            seek(&mut index_file, SeekFrom::Start(pos), stats).await?;
-            let min0 = 4 + 2 * self.hver.offset_size();
-            rb.fill_min(&mut index_file, min0, stats).await?;
-            let buf = rb.data();
-            let e = parse_name_hash_channel_entry(buf, self.hver.as_ref())?;
-            let next = e.next;
-            entries.push(e);
-            pos = next;
-        }
-        for e in &entries {
-            if e.channel_name == channel_name {
-                let hver = self.hver.duplicate();
-                let pos = RtreePos(e.id_rtree_pos);
-                // TODO Rtree could reuse the File here:
-                let tree = Rtree::new(self.path.clone(), index_file, pos, hver, stats).await?;
-                return Ok(Some(tree));
-            }
-        }
-        Ok(None)
-    }
-}
-
 #[derive(Debug)]
 pub struct RTreeNodeRecord {
     pub ts1: Nanos,
@@ -286,10 +286,10 @@ pub async fn read_rtree_node(
     const OFF1: usize = 9;
     const RLEN: usize = 24;
     const NANO_MAX: u32 = 999999999;
-    seek(file, SeekFrom::Start(pos.into()), stats).await?;
-    let mut rb = RingBuf::new();
+    // TODO should not be used.
+    let mut rb = RingBuf::new(file, pos.pos, stats.clone()).await?;
     // TODO must know how much data I need at least...
-    rb.fill_min(file, OFF1 + rtree_m * RLEN, stats).await?;
+    rb.fill_min(OFF1 + rtree_m * RLEN).await?;
     if false {
         let s = format_hex_block(rb.data(), 128);
         info!("RTREE NODE:\n{}", s);
@@ -423,7 +423,7 @@ impl RtreeNodeAtRecord {
 #[derive(Debug)]
 pub struct Rtree {
     path: PathBuf,
-    file: File,
+    rb: RingBuf<File>,
     m: usize,
     root: NodePos,
     hver: Box<dyn HeaderVersion>,
@@ -438,10 +438,10 @@ impl Rtree {
         stats: &StatsChannel,
     ) -> Result<Self, Error> {
         let mut file = file;
-        let (m, root) = Self::read_entry(&mut file, pos, hver.as_ref(), stats).await?;
+        let (m, root) = Self::read_entry(&mut file, pos.clone(), hver.as_ref(), stats).await?;
         let ret = Self {
             path: path.as_ref().into(),
-            file,
+            rb: RingBuf::new(file, pos.0, stats.clone()).await?,
             m,
             root,
             hver,
@@ -455,11 +455,10 @@ impl Rtree {
         hver: &dyn HeaderVersion,
         stats: &StatsChannel,
     ) -> Result<(usize, NodePos), Error> {
-        seek(file, SeekFrom::Start(pos.0), stats).await?;
-        let mut rb = RingBuf::new();
+        let mut rb = RingBuf::new(file, pos.0, stats.clone()).await?;
         // TODO should be able to indicate how much I need at most before I know that I will e.g. seek or abort.
         let min0 = hver.offset_size() + 4;
-        rb.fill_min(file, min0, stats).await?;
+        rb.fill_min(min0).await?;
         if rb.len() < min0 {
             return Err(Error::with_msg_no_trace("could not read enough"));
         }
@@ -475,14 +474,13 @@ impl Rtree {
         Ok(ret)
     }
 
-    pub async fn read_node_at(&mut self, pos: NodePos, stats: &StatsChannel) -> Result<RtreeNode, Error> {
-        let file = &mut self.file;
-        seek(file, SeekFrom::Start(pos.0), stats).await?;
-        let mut rb = RingBuf::new();
+    pub async fn read_node_at(&mut self, pos: NodePos, _stats: &StatsChannel) -> Result<RtreeNode, Error> {
+        let rb = &mut self.rb;
+        rb.seek(pos.0).await?;
         let off1 = 1 + self.hver.offset_size();
         let rlen = 4 * 4 + self.hver.offset_size();
         let min0 = off1 + self.m * rlen;
-        rb.fill_min(file, min0, stats).await?;
+        rb.fill_min(min0).await?;
         if false {
             let s = format_hex_block(rb.data(), min0);
             trace!("RTREE NODE:\n{}", s);
@@ -498,9 +496,10 @@ impl Rtree {
         if false {
             trace!("is_leaf: {}  parent: {:?}", is_leaf, parent);
         }
+        let hver = self.hver.duplicate();
         let recs = (0..self.m)
             .into_iter()
-            .filter_map(|i| {
+            .filter_map(move |i| {
                 const NANO_MAX: u32 = 999999999;
                 let off2 = off1 + i * rlen;
                 let ts1a = readu32(buf, off2 + 0);
@@ -511,7 +510,7 @@ impl Rtree {
                 let ts2b = ts2b.min(NANO_MAX);
                 let ts1 = ts1a as u64 * SEC + ts1b as u64 + EPICS_EPOCH_OFFSET;
                 let ts2 = ts2a as u64 * SEC + ts2b as u64 + EPICS_EPOCH_OFFSET;
-                let target = self.hver.read_offset(buf, off2 + 16);
+                let target = hver.read_offset(buf, off2 + 16);
                 //trace!("NODE   {} {}   {} {}   {}", ts1a, ts1b, ts2a, ts2b, child_or_id);
                 if target != 0 && ts2 != 0 {
                     let target = if is_leaf {
@@ -586,7 +585,7 @@ impl Rtree {
         let file = open_read(self.path.clone(), stats).await?;
         let ret = Self {
             path: self.path.clone(),
-            file: file,
+            rb: RingBuf::new(file, 0, stats.clone()).await?,
             m: self.m,
             root: self.root.clone(),
             hver: self.hver.duplicate(),
@@ -669,10 +668,9 @@ pub async fn read_rtree_entrypoint(
     _basics: &IndexFileBasics,
     stats: &StatsChannel,
 ) -> Result<RTreeNode, Error> {
-    seek(file, SeekFrom::Start(pos), stats).await?;
-    let mut rb = RingBuf::new();
+    let mut rb = RingBuf::new(file, pos, stats.clone()).await?;
     // TODO remove, this is anyway still using a hardcoded offset size.
-    rb.fill_min(file, 8 + 4, stats).await?;
+    rb.fill_min(8 + 4).await?;
     if rb.len() < 8 + 4 {
         return Err(Error::with_msg_no_trace("could not read enough"));
     }
@@ -681,7 +679,8 @@ pub async fn read_rtree_entrypoint(
     let rtree_m = readu32(b, 8);
     //info!("node_offset: {}  rtree_m: {}", node_offset, rtree_m);
     let pos = FilePos { pos: node_offset };
-    let node = read_rtree_node(file, pos, rtree_m as usize, stats).await?;
+    let mut file = rb.into_file();
+    let node = read_rtree_node(&mut file, pos, rtree_m as usize, stats).await?;
     //info!("read_rtree_entrypoint   READ ROOT NODE: {:?}", node);
     Ok(node)
 }
@@ -829,17 +828,17 @@ pub async fn read_channel(
     stats: &StatsChannel,
 ) -> Result<Option<ChannelInfoBasics>, Error> {
     let path = path.into();
-    let mut basics = read_file_basics(path.clone(), index_file, stats).await?;
+    let mut index_file = index_file;
+    let basics = read_file_basics(path.clone(), &mut index_file, stats).await?;
     let chn_hash = name_hash(channel_name, basics.name_hash_anchor_len as u32);
     let epos = &basics.name_hash_entries[chn_hash as usize];
     let mut entries = vec![];
-    let mut rb = RingBuf::new();
     let mut pos = epos.named_hash_channel_entry_pos;
+    let mut rb = RingBuf::new(index_file, pos, stats.clone()).await?;
     loop {
-        rb.reset();
-        seek(&mut basics.file, SeekFrom::Start(pos), stats).await?;
+        rb.seek(pos).await?;
         let fill_min = if basics.hver.offset_size() == 8 { 20 } else { 12 };
-        rb.fill_min(&mut basics.file, fill_min, stats).await?;
+        rb.fill_min(fill_min).await?;
         if rb.len() < fill_min {
             warn!("not enough data to continue reading channel list from name hash list");
             break;
@@ -930,10 +929,9 @@ pub async fn read_datablockref(
     hver: &dyn HeaderVersion,
     stats: &StatsChannel,
 ) -> Result<Dataref, Error> {
-    seek(file, SeekFrom::Start(pos.pos), stats).await?;
-    let mut rb = RingBuf::new();
+    let mut rb = RingBuf::new(file, pos.pos, stats.clone()).await?;
     let min0 = hver.offset_size() * 2 + 2;
-    rb.fill_min(file, min0, stats).await?;
+    rb.fill_min(min0).await?;
     let buf = rb.data();
     let mut p = 0;
     let next = hver.read_offset(buf, p);
@@ -943,7 +941,37 @@ pub async fn read_datablockref(
     let len = readu16(buf, p) as usize;
     p += 2;
     let _ = p;
-    rb.fill_min(file, min0 + len, stats).await?;
+    rb.fill_min(min0 + len).await?;
+    let buf = rb.data();
+    let fname = String::from_utf8(buf[min0..min0 + len].to_vec())?;
+    let next = DatarefPos(next);
+    let data_header_pos = DataheaderPos(data);
+    let ret = Dataref {
+        next,
+        data_header_pos,
+        fname,
+    };
+    Ok(ret)
+}
+
+pub async fn read_datablockref2(
+    rb: &mut BackReadBuf<File>,
+    pos: DatarefPos,
+    hver: &dyn HeaderVersion,
+) -> Result<Dataref, Error> {
+    rb.seek(pos.0).await?;
+    let min0 = hver.offset_size() * 2 + 2;
+    rb.fill_min(min0).await?;
+    let buf = rb.data();
+    let mut p = 0;
+    let next = hver.read_offset(buf, p);
+    p += hver.offset_size();
+    let data = hver.read_offset(buf, p);
+    p += hver.offset_size();
+    let len = readu16(buf, p) as usize;
+    p += 2;
+    let _ = p;
+    rb.fill_min(min0 + len).await?;
     let buf = rb.data();
     let fname = String::from_utf8(buf[min0..min0 + len].to_vec())?;
     let next = DatarefPos(next);
@@ -964,12 +992,11 @@ async fn channel_list_from_index_name_hash_list(
 ) -> Result<Vec<NamedHashChannelEntry>, Error> {
     let mut pos = pos;
     let mut ret = vec![];
-    let mut rb = RingBuf::new();
+    let mut rb = RingBuf::new(file, pos.pos, stats.clone()).await?;
     loop {
-        rb.reset();
-        seek(file, SeekFrom::Start(pos.pos), stats).await?;
+        rb.seek(pos.pos).await?;
         let fill_min = if hver.offset_size() == 8 { 20 } else { 12 };
-        rb.fill_min(file, fill_min, stats).await?;
+        rb.fill_min(fill_min).await?;
         if rb.len() < fill_min {
             warn!("not enough data to continue reading channel list from name hash list");
             break;
@@ -989,8 +1016,8 @@ async fn channel_list_from_index_name_hash_list(
 // TODO retire this function
 pub async fn channel_list(index_path: PathBuf, stats: &StatsChannel) -> Result<Vec<String>, Error> {
     let mut ret = vec![];
-    let file = open_read(index_path.clone(), stats).await?;
-    let mut basics = read_file_basics(index_path.clone(), file, stats).await?;
+    let mut file = open_read(index_path.clone(), stats).await?;
+    let basics = read_file_basics(index_path.clone(), &mut file, stats).await?;
     let hver2 = HeaderVersion2;
     let hver3 = HeaderVersion3;
     let hver: &dyn HeaderVersion = if basics.version == 2 {
@@ -1008,7 +1035,7 @@ pub async fn channel_list(index_path: PathBuf, stats: &StatsChannel) -> Result<V
             let pos = FilePos {
                 pos: name_hash_entry.named_hash_channel_entry_pos,
             };
-            let list = channel_list_from_index_name_hash_list(&mut basics.file, pos, hver, stats).await?;
+            let list = channel_list_from_index_name_hash_list(&mut file, pos, hver, stats).await?;
             for e in list {
                 ret.push(e.channel_name);
             }
@@ -1040,8 +1067,8 @@ mod test {
     fn read_file_basic_info() -> Result<(), Error> {
         let fut = async {
             let stats = &StatsChannel::dummy();
-            let file = open_read(CHN_0_MASTER_INDEX.into(), stats).await?;
-            let res = read_file_basics(CHN_0_MASTER_INDEX.into(), file, stats).await?;
+            let mut file = open_read(CHN_0_MASTER_INDEX.into(), stats).await?;
+            let res = read_file_basics(CHN_0_MASTER_INDEX.into(), &mut file, stats).await?;
             assert_eq!(res.version, 3);
             assert_eq!(res.name_hash_anchor_beg, 88);
             assert_eq!(res.name_hash_anchor_len, 1009);
@@ -1062,7 +1089,8 @@ mod test {
         let fut = async {
             let stats = &StatsChannel::dummy();
             let channel_name = "X05DA-FE-WI1:TC1";
-            let basics = IndexFileBasics::from_path(CHN_0_MASTER_INDEX, stats).await?;
+            let mut file = open_read(CHN_0_MASTER_INDEX.into(), stats).await?;
+            let basics = IndexFileBasics::from_file(CHN_0_MASTER_INDEX, &mut file, stats).await?;
             let tree = basics.rtree_for_channel(channel_name, stats).await?;
             let tree = tree.ok_or_else(|| Error::with_msg("no tree found for channel"))?;
             assert_eq!(tree.m, 50);
@@ -1078,7 +1106,8 @@ mod test {
             let stats = &StatsChannel::dummy();
             let channel_name = "X05DA-FE-WI1:TC1";
             let range = NanoRange { beg: 0, end: u64::MAX };
-            let basics = IndexFileBasics::from_path(CHN_0_MASTER_INDEX, stats).await?;
+            let mut file = open_read(CHN_0_MASTER_INDEX.into(), stats).await?;
+            let basics = IndexFileBasics::from_file(CHN_0_MASTER_INDEX, &mut file, stats).await?;
             let mut tree = basics
                 .rtree_for_channel(channel_name, stats)
                 .await?
@@ -1114,7 +1143,8 @@ mod test {
                 beg: 1601503499684884156,
                 end: 1601569919634086480,
             };
-            let basics = IndexFileBasics::from_path(CHN_0_MASTER_INDEX, stats).await?;
+            let mut file = open_read(CHN_0_MASTER_INDEX.into(), stats).await?;
+            let basics = IndexFileBasics::from_file(CHN_0_MASTER_INDEX, &mut file, stats).await?;
             let mut tree = basics
                 .rtree_for_channel(channel_name, stats)
                 .await?
diff --git a/archapp/src/archeng/ringbuf.rs b/archapp/src/archeng/ringbuf.rs
new file mode 100644
index 0000000..4cd9002
--- /dev/null
+++ b/archapp/src/archeng/ringbuf.rs
@@ -0,0 +1,135 @@
+use crate::archeng::{read, seek, StatsChannel};
+use err::Error;
+use netpod::log::*;
+use std::fmt;
+use std::mem::ManuallyDrop;
+use std::{borrow::BorrowMut, io::SeekFrom};
+use tokio::fs::File;
+
+pub struct RingBuf<F> {
+    file: Option<F>,
+    buf: Vec<u8>,
+    abs: usize,
+    wp: usize,
+    rp: usize,
+    stats: StatsChannel,
+    seek_request: u64,
+    seek_done: u64,
+    read_done: u64,
+}
+
+impl<F> RingBuf<F>
+where
+    F: BorrowMut<File>,
+{
+    pub async fn new(file: F, pos: u64, stats: StatsChannel) -> Result<Self, Error> {
+        let mut ret = Self {
+            file: Some(file),
+            buf: vec![0; 1024 * 1024],
+            abs: usize::MAX,
+            wp: 0,
+            rp: 0,
+            stats,
+            seek_request: 0,
+            seek_done: 0,
+            read_done: 0,
+        };
+        ret.seek(pos).await?;
+        Ok(ret)
+    }
+
+    pub fn into_file(mut self) -> F {
+        self.file.take().unwrap()
+    }
+
+    pub fn len(&self) -> usize {
+        self.wp - self.rp
+    }
+
+    pub fn adv(&mut self, n: usize) {
+        self.rp += n;
+    }
+
+    pub fn data(&self) -> &[u8] {
+        &self.buf[self.rp..self.wp]
+    }
+
+    async fn fill(&mut self) -> Result<usize, Error> {
+        if self.rp == self.wp {
+            if self.rp != 0 {
+                self.wp = 0;
+                self.rp = 0;
+            }
+        } else {
+            unsafe {
+                std::ptr::copy::<u8>(&self.buf[self.rp], &mut self.buf[0], self.len());
+                self.wp -= self.rp;
+                self.rp = 0;
+            }
+        }
+        let n = read(
+            self.file.as_mut().unwrap().borrow_mut(),
+            &mut self.buf[self.wp..],
+            &self.stats,
+        )
+        .await?;
+        self.wp += n;
+        self.read_done += 1;
+        Ok(n)
+    }
+
+    pub async fn fill_min(&mut self, min: usize) -> Result<usize, Error> {
+        let len = self.len();
+        while self.len() < min {
+            let n = self.fill().await?;
+            if n == 0 {
+                return Err(Error::with_msg_no_trace(format!("fill_min can not read min {}", min)));
+            }
+        }
+        Ok(self.len() - len)
+    }
+
+    pub async fn seek(&mut self, pos: u64) -> Result<u64, Error> {
+        let dp = pos as i64 - self.abs as i64 - self.rp as i64;
+        if dp < 0 && dp > -2048 {
+            debug!("small NEG seek {}", dp);
+        } else if dp == 0 {
+            debug!("zero seek");
+        } else if dp > 0 && dp < 2048 {
+            debug!("small POS seek {}", dp);
+        }
+        self.abs = pos as usize;
+        self.rp = 0;
+        self.wp = 0;
+        let ret = seek(
+            self.file.as_mut().unwrap().borrow_mut(),
+            SeekFrom::Start(pos),
+            &self.stats,
+        )
+        .await
+        .map_err(|e| Error::from(e))?;
+        self.seek_request += 1;
+        self.seek_done += 1;
+        Ok(ret)
+    }
+
+    pub fn rp_abs(&self) -> u64 {
+        self.abs as u64 + self.rp as u64
+    }
+}
+
+impl<F> fmt::Debug for RingBuf<F> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("RingBuf")
+            .field("abs", &self.abs)
+            .field("wp", &self.wp)
+            .field("rp", &self.rp)
+            .finish()
+    }
+}
+
+impl<F> Drop for RingBuf<F> {
+    fn drop(&mut self) {
+        info!("RingBuf  Drop  {}  {}", self.seek_request, self.read_done);
+    }
+}
diff --git a/taskrun/src/lib.rs b/taskrun/src/lib.rs
index 0c4e7ea..9638254 100644
--- a/taskrun/src/lib.rs
+++ b/taskrun/src/lib.rs
@@ -96,6 +96,8 @@ pub fn tracing_init() {
                     "archapp::archeng::datablockstream=info",
                     "archapp::archeng::indextree=info",
                     "archapp::archeng::blockstream=trace",
+                    "archapp::archeng::ringbuf=trace",
+                    "archapp::archeng::backreadbuf=trace",
                     "archapp::storagemerge=info",
                     "daqbuffer::test=trace",
                 ]