From ad9620786898024e4324df8ab534da2cc0e7168a Mon Sep 17 00:00:00 2001
From: "Jonathan A. Sternberg" <jonathan@influxdb.com>
Date: Tue, 22 Mar 2016 09:36:27 -0400
Subject: [PATCH] Fix ORDER BY desc so it doesn't skip values

After reading the initial buffer, ORDER BY desc would read the next
block into the buffer and only read the first element. It's because the
code that was copied from the ascending cursor wasn't modified correctly
to set the position to the last element in the buffer.

The buffer size has also been lowered from 1000 to 10 to match with the
ascending cursor for performance with limit queries.

Fixes #6055.
---
 tsdb/engine/tsm1/iterator.gen.go      | 16 ++++++++--------
 tsdb/engine/tsm1/iterator.gen.go.tmpl |  4 ++--
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/tsdb/engine/tsm1/iterator.gen.go b/tsdb/engine/tsm1/iterator.gen.go
index 0a1e19df9f..988e0fd623 100644
--- a/tsdb/engine/tsm1/iterator.gen.go
+++ b/tsdb/engine/tsm1/iterator.gen.go
@@ -338,7 +338,7 @@ func newFloatDescendingCursor(seek int64, cacheValues Values, tsmKeyCursor *KeyC
 	}
 
 	c.tsm.keyCursor = tsmKeyCursor
-	c.tsm.buf = make([]FloatValue, 1000)
+	c.tsm.buf = make([]FloatValue, 10)
 	c.tsm.values, _ = c.tsm.keyCursor.ReadFloatBlock(c.tsm.buf)
 	c.tsm.pos = sort.Search(len(c.tsm.values), func(i int) bool {
 		return c.tsm.values[i].UnixNano() >= seek
@@ -418,7 +418,7 @@ func (c *floatDescendingCursor) nextTSM() {
 		if len(c.tsm.values) == 0 {
 			return
 		}
-		c.tsm.pos = 0
+		c.tsm.pos = len(c.tsm.values) - 1
 	}
 }
 
@@ -681,7 +681,7 @@ func newIntegerDescendingCursor(seek int64, cacheValues Values, tsmKeyCursor *Ke
 	}
 
 	c.tsm.keyCursor = tsmKeyCursor
-	c.tsm.buf = make([]IntegerValue, 1000)
+	c.tsm.buf = make([]IntegerValue, 10)
 	c.tsm.values, _ = c.tsm.keyCursor.ReadIntegerBlock(c.tsm.buf)
 	c.tsm.pos = sort.Search(len(c.tsm.values), func(i int) bool {
 		return c.tsm.values[i].UnixNano() >= seek
@@ -761,7 +761,7 @@ func (c *integerDescendingCursor) nextTSM() {
 		if len(c.tsm.values) == 0 {
 			return
 		}
-		c.tsm.pos = 0
+		c.tsm.pos = len(c.tsm.values) - 1
 	}
 }
 
@@ -1024,7 +1024,7 @@ func newStringDescendingCursor(seek int64, cacheValues Values, tsmKeyCursor *Key
 	}
 
 	c.tsm.keyCursor = tsmKeyCursor
-	c.tsm.buf = make([]StringValue, 1000)
+	c.tsm.buf = make([]StringValue, 10)
 	c.tsm.values, _ = c.tsm.keyCursor.ReadStringBlock(c.tsm.buf)
 	c.tsm.pos = sort.Search(len(c.tsm.values), func(i int) bool {
 		return c.tsm.values[i].UnixNano() >= seek
@@ -1104,7 +1104,7 @@ func (c *stringDescendingCursor) nextTSM() {
 		if len(c.tsm.values) == 0 {
 			return
 		}
-		c.tsm.pos = 0
+		c.tsm.pos = len(c.tsm.values) - 1
 	}
 }
 
@@ -1367,7 +1367,7 @@ func newBooleanDescendingCursor(seek int64, cacheValues Values, tsmKeyCursor *Ke
 	}
 
 	c.tsm.keyCursor = tsmKeyCursor
-	c.tsm.buf = make([]BooleanValue, 1000)
+	c.tsm.buf = make([]BooleanValue, 10)
 	c.tsm.values, _ = c.tsm.keyCursor.ReadBooleanBlock(c.tsm.buf)
 	c.tsm.pos = sort.Search(len(c.tsm.values), func(i int) bool {
 		return c.tsm.values[i].UnixNano() >= seek
@@ -1447,7 +1447,7 @@ func (c *booleanDescendingCursor) nextTSM() {
 		if len(c.tsm.values) == 0 {
 			return
 		}
-		c.tsm.pos = 0
+		c.tsm.pos = len(c.tsm.values) - 1
 	}
 }
 
diff --git a/tsdb/engine/tsm1/iterator.gen.go.tmpl b/tsdb/engine/tsm1/iterator.gen.go.tmpl
index 578f77e682..da6f5c1ec1 100644
--- a/tsdb/engine/tsm1/iterator.gen.go.tmpl
+++ b/tsdb/engine/tsm1/iterator.gen.go.tmpl
@@ -334,7 +334,7 @@ func new{{.Name}}DescendingCursor(seek int64, cacheValues Values, tsmKeyCursor *
 	}
 
 	c.tsm.keyCursor = tsmKeyCursor
-	c.tsm.buf = make([]{{.Name}}Value, 1000)
+	c.tsm.buf = make([]{{.Name}}Value, 10)
 	c.tsm.values, _ = c.tsm.keyCursor.Read{{.Name}}Block(c.tsm.buf)
 	c.tsm.pos = sort.Search(len(c.tsm.values), func(i int) bool {
 		return c.tsm.values[i].UnixNano() >= seek
@@ -414,7 +414,7 @@ func (c *{{.name}}DescendingCursor) nextTSM() {
 		if len(c.tsm.values) == 0 {
 			return
 		}
-		c.tsm.pos = 0
+		c.tsm.pos = len(c.tsm.values) - 1
 	}
 }