.

t/neo/storage/fs1/xbufio.go

@@ -33,6 +33,7 @@ import (
 
 
 // SeqBufReader implements buffering for a io.ReaderAt optimized for sequential access
+// Both forward, backward and interleaved forward/backward access patterns are supported	XXX
 // FIXME access from multiple goroutines? (it is required per io.ReaderAt
 // interface, but for sequential workloads we do not need it)
 // XXX -> xbufio.SeqReader
@@ -41,8 +42,13 @@ type SeqBufReader struct {
 	buf	[]byte
 	pos	int64
 
-	// position of last IO  (can be != .pos because large reads are not buffered)
-	posLastIO int64
+	// // position of last IO  (can be != .pos because large reads are not buffered)
+	// posLastIO int64
+
+	// TODO text
+	posLastAccess	int64
+	posLastFwdAfter	int64
+	posLastBackward	int64
 
 	r io.ReaderAt
 }
@@ -55,7 +61,7 @@ func NewSeqBufReader(r io.ReaderAt) *SeqBufReader {
 }
 
 func NewSeqBufReaderSize(r io.ReaderAt, size int) *SeqBufReader {
-	sb := &SeqBufReader{r: r, pos: 0, buf: make([]byte, 0, size), posLastIO: 0}
+	sb := &SeqBufReader{r: r, pos: 0, buf: make([]byte, 0, size)}	//, posLastIO: 0}
 	return sb
 }
 
@@ -66,13 +72,25 @@ func NewSeqBufReaderSize(r io.ReaderAt, size int) *SeqBufReader {
 // }
 
 func (sb *SeqBufReader) ReadAt(p []byte, pos int64) (int, error) {
+	// read-in last access positions and update them in *sb with current ones for next read
+	posLastAccess := sb.posLastAccess
+	posLastFwdAfter := sb.posLastFwdAfter
+	posLastBackward := sb.posLastBackward
+	sb.posLastAccess = pos
+	if pos >= posLastAccess {
+		sb.posLastFwdAfter = pos + len64(p)
+	} else {
+		sb.posLastBackward = pos
+	}
+
 	// if request size > buffer - read data directly
 	if len(p) > cap(sb.buf) {
 		// no copying from sb.buf here at all as if e.g. we could copy from sb.buf, the
 		// kernel can copy the same data from pagecache as well, and it will take the same time
 		// because for data in sb.buf corresponding page in pagecache has high p. to be hot.
 		//log.Printf("READ [%v, %v)\t#%v", pos, pos + len64(p), len(p))
-		sb.posLastIO = pos
+		//sb.posLastIO = pos
+		// TODO update lastAccess & lastFwd/lastBack
 		return sb.r.ReadAt(p, pos)
 	}
 
@@ -122,13 +140,42 @@ func (sb *SeqBufReader) ReadAt(p []byte, pos int64) (int, error) {
 	// NOTE len(p) <= cap(sb.buf)
 	var xpos int64 // position for new IO request
 
-	if pos >= sb.posLastIO {
+	//if pos >= sb.posLastIO {
+	if pos >= posLastAccess {
 		// forward
 		xpos = pos
 
+		// if forward trend continues and buffering can be made adjacent to
+		// previous forward access - shift reading down right to after it.
+		xLastAfter := posLastFwdAfter + int64(nhead)	// XXX comment
+		if xLastAfter <= xpos && xpos + len64(p) <= xLastAfter + cap64(sb.buf) {
+			xpos = xLastAfter
+		}
+
+		// XXX symmetry for "alternatively" in backward case
+
 	} else {
 		// backward
+		xpos = pos
+
+		// if backward trend continues and bufferring would overlap with
+		// previous backward access - shift reading up right to it.
+		if xpos < posLastBackward && posLastBackward < xpos + cap64(sb.buf) {
+			xpos = max64(posLastBackward, xpos + len64(p)) - cap64(sb.buf)
+
+		// XXX recheck do we really need this ?	( was added for {122, 6, 121, 10} )
+		// XXX alternatively even if backward trend does not continue anymore
+		// but if this will overlap with last access (XXX load) range, probably
+		// it is better (we are optimizing for sequential access) to
+		// shift loading region down not to overlap.
+		} else if xpos + cap64(sb.buf) > posLastAccess {
+			xpos = max64(posLastAccess, xpos + len64(p)) - cap64(sb.buf)
+		}
+
+		// don't let reading go beyond start of the file
+		xpos = max64(xpos, 0)
 
+		/*
 		// by default we want to read forward, even when iterating backward:
 		// there are frequent jumps backward for reading a record there forward
 		xpos = pos
@@ -141,14 +188,15 @@ func (sb *SeqBufReader) ReadAt(p []byte, pos int64) (int, error) {
 		// can overlap, if e.g. last access was big non-buffered read.
 		if xpos + cap64(sb.buf) > sb.posLastIO {
 			xpos = max64(sb.posLastIO, xpos + len64(p)) - cap64(sb.buf)
-		}
 
-		// don't let reading go beyond start of the file
-		xpos = max64(xpos, 0)
+			// don't let reading go beyond start of the file
+			xpos = max64(xpos, 0)
+		}
+		*/
 	}
 
 	//log.Printf("read [%v, %v)\t#%v", xpos, xpos + cap64(sb.buf), cap(sb.buf))
-	sb.posLastIO = xpos
+//	sb.posLastIO = xpos
 	nn, err := sb.r.ReadAt(sb.buf[:cap(sb.buf)], xpos)
 
 	// even if there was an error, or data partly read, we cannot retain
@@ -169,9 +217,9 @@ func (sb *SeqBufReader) ReadAt(p []byte, pos int64) (int, error) {
 		// - it was backward reading, and
 		// - original requst was narrower than buffer
 		// try to satisfy it once again directly
-		if pos != xpos {
+		if pos != xpos {	// FIXME pos != xpos no longer means backward
 			//log.Printf("read [%v, %v)\t#%v", pos, pos + len64(p), len(p))
-			sb.posLastIO = pos
+//			sb.posLastIO = pos
 			nn, err = sb.r.ReadAt(p, pos)
 			if nn < len(p) {
 				return nn, err

t/neo/storage/fs1/xbufio_test.go

@@ -9,6 +9,8 @@ import (
 	"errors"
 	"io"
 	"testing"
+
+	"fmt"
 )
 
 
@@ -41,14 +43,15 @@ func (r *XReader) ReadAt(p []byte, pos int64) (n int, err error) {
 
 // read @pos/len -> rb.pos, len(rb.buf)
 var xSeqBufTestv = []struct {pos int64; Len int; bufPos int64; bufLen int} {
+	// TODO add trend / not trend everywhere
 	{40,  5, 40, 10},	// 1st access, forward by default
-	{45,  7, 50, 10},	// part taken from buf, part read next, forward
+	{45,  7, 50, 10},	// part taken from buf, part read next, forward (trend)
 	{52,  5, 50, 10},	// everything taken from buf
-	{57,  5, 60, 10},	// part taken from buf, part read next
+	{57,  5, 60, 10},	// part taken from buf, part read next (trend)
 	{60, 11, 60, 10},	// access > cap(buf), buf skipped
 	{71, 11, 60, 10},	// access > cap(buf), once again
 	{82, 10, 82, 10},	// access = cap(buf), should refill buf
-	{92,  5, 92,  8},	// next access - should refill buffer, but only up to EIO range
+	{92,  5, 92,  8},	// next access - should refill buffer (trend), but only up to EIO range
 	{97,  4, 100, 0},	// this triggers user-visible EIO, buffer scratched
 	{101, 5, 101, 0},	// EIO again
 	{105, 5, 105, 10},	// past EIO range - buffer refilled
@@ -57,7 +60,7 @@ var xSeqBufTestv = []struct {pos int64; Len int; bufPos int64; bufLen int} {
 	{110,70, 98,  2},	// very big access forward, buf untouched
 	{180,70, 98,  2},	// big access ~ forward
 
-	{172, 5, 170, 10},	// backward: buffer refilled up to posLastIO
+	{170, 5, 170, 10},	// backward: buffer refilled forward because prev backward reading was below
 	{168, 4, 160, 10},	// backward: buffer refilled backward
 	{162, 6, 160, 10},	// backward: all data read from buffer
 	{150,12, 160, 10},	// big backward: buf untouched
@@ -68,28 +71,48 @@ var xSeqBufTestv = []struct {pos int64; Len int; bufPos int64; bufLen int} {
 	{122, 6, 121, 10},	// backward after forward: buf refilled backward
 	{131, 9, 131, 10},	// forward again
 	{136,20, 131, 10},	// big forward starting from inside filled buf
-	{128, 4, 126, 10},	// backward: buf refilled up to posLastIO
+	{128, 4, 126, 10},	// backward (not trend): buf refilled up to posLastIO
+
+	// TODO interleaved forward + back-back-back
+	// TODO interleaved backward + fwd-fwd-fwd
 
 	{5, 4, 5, 10},		// forward near file start
 	{2, 3, 0, 10},		// backward: buf does not go beyong 0
 
 	{40, 0, 0, 10},		// zero-sized out-of-buffer read do not change buffer
 
-	// backward vs EIO
-	{110, 1, 110, 10},	// reset state: forward @110
-	{105, 7, 100,  0},	// backward client after EIO: buf scratched but read request satisfied
-	{110, 1, 110, 10},	// reset @110
-	{103, 5, 100,  0},	// backward overlapping tail EIO: buf scratched, EIO -> user
-	{110, 1, 110, 10},	// reset @110
-	{101, 2, 100,  0},	// backward inside EIO range: buf scratched, EIO -> user
-	{108, 1, 108, 10},	// reset @108
-	{100, 4,  98,  2},	// backward = EIO range: buf filled < EIO range, EIO -> user
-	{108, 1, 108, 10},	// reset @108
+	// backward (not trend) vs EIO
+	{108,10, 108, 10},	// reset @108
+	{ 98, 1,  98,  2},	// backward not overlapping EIO: buf filled < EIO range
+	{108,10, 108, 10},	// reset @108
+	{ 99, 4,  98,  2},	// backward overlapping head EIO: buf filled < EIO range, EIO -> user
+	{108,10, 108, 10},	// reset @108
 	{ 99, 6,  98,  2},	// backward overlapping whole EIO range: buf filled <= EIO range, EIO -> user
-	{108, 1, 108, 10},	// reset @108
+	{108,10, 108, 10},	// reset @108
+	{100, 4,  98,  2},	// backward = EIO range: buf filled < EIO range, EIO -> user
+	{110,10, 110, 10},	// reset @110
+	{101, 2, 100,  0},	// backward inside EIO range: buf scratched, EIO -> user
+	{110,10, 110, 10},	// reset @110
+	{103, 5, 100,  0},	// backward overlapping tail EIO: buf scratched, EIO -> user
+	{110,10, 110, 10},	// reset state: forward @110
+	{105, 7, 100,  0},	// backward client after EIO: buf scratched but read request satisfied
+
+	// backward (trend) vs EIO
+	// NOTE this is reverse of `backward (not trend) vs EIO
+	{110,10, 110, 10},	// reset state: forward @110
+	{105, 7, 100,  0},	// backward client after EIO: buf scratched but read request satisfied
+	{110,10, 110, 10},	// reset @110
+	{103, 5,  98,  2},	// backward overlapping tail EIO: buf scratched (XXX), EIO -> user
+	{110,10, 110, 10},	// reset @110
+	{101, 2,  93,  7},	// backward inside EIO range: buf scratched (XXX), EIO -> user
+	{108,10, 108, 10},	// reset @108
+	{100, 4,  94,  6},	// backward = EIO range: buf filled < EIO range, EIO -> user
+	{108,10, 108, 10},	// reset @108
+	{ 99, 6,  95,  5},	// backward overlapping whole EIO range: buf filled <= EIO range, EIO -> user
+	{108,10, 108, 10},	// reset @108
 	{ 99, 4,  98,  2},	// backward overlapping head EIO: buf filled < EIO range, EIO -> user
-	{108, 1, 108, 10},	// reset @108
-	{ 98, 1,  98,  2},	// nackward not overlapping EIO: buf filled < EIO range
+	{108,10, 108, 10},	// reset @108
+	{ 98, 1,  89, 10},	// backward not overlapping EIO: buf filled according to backward trend
 
 	{250, 4, 250,  6},	// access near EOF - buffer fill hits EOF, but not returns it to client
 	{254, 5, 256,  0},	// access overlapping EOF - EOF returned, buf scratched
@@ -103,6 +126,7 @@ func TestSeqBufReader(t *testing.T) {
 	rb := NewSeqBufReaderSize(r, 10) // with 10 it is easier to do/check math for a human
 
 	for _, tt := range xSeqBufTestv {
+		fmt.Println(tt)
 		pOk := make([]byte, tt.Len)
 		pB  := make([]byte, tt.Len)