From 782ead0dbf3095d0e843c2036bf40cc8ecd9b4d1 Mon Sep 17 00:00:00 2001
From: Ben Johnson <benbjohnson@yahoo.com>
Date: Mon, 19 May 2014 12:08:33 -0600
Subject: Fix freelist allocation direction.

This commit fixes the freelist so that it frees from the beginning of the data file
instead of the end. It also adds a fast path for pages which can be allocated from
the first free pages and it includes read transaction stats.
---
 db.go | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

(limited to 'db.go')

diff --git a/db.go b/db.go
index c768ce3..ed0f2cd 100644
--- a/db.go
+++ b/db.go
@@ -351,7 +351,6 @@ func (db *DB) beginTx() (*Tx, error) {
 
 	// Lock the meta pages while we initialize the transaction.
 	db.metalock.Lock()
-	defer db.metalock.Unlock()
 
 	// Exit if the database is not open yet.
 	if !db.opened {
@@ -365,6 +364,16 @@ func (db *DB) beginTx() (*Tx, error) {
 
 	// Keep track of transaction until it closes.
 	db.txs = append(db.txs, t)
+	n := len(db.txs)
+
+	// Unlock the meta pages.
+	db.metalock.Unlock()
+
+	// Update the transaction stats.
+	db.statlock.Lock()
+	db.stats.TxN++
+	db.stats.OpenTxN = n
+	db.statlock.Unlock()
 
 	return t, nil
 }
@@ -418,12 +427,14 @@ func (db *DB) removeTx(tx *Tx) {
 			break
 		}
 	}
+	n := len(db.txs)
 
 	// Unlock the meta pages.
 	db.metalock.Unlock()
 
 	// Merge statistics.
 	db.statlock.Lock()
+	db.stats.OpenTxN = n
 	db.stats.TxStats.add(&tx.stats)
 	db.statlock.Unlock()
 }
@@ -612,6 +623,10 @@ func (db *DB) allocate(count int) (*page, error) {
 
 // Stats represents statistics about the database.
 type Stats struct {
+	// Transaction stats
+	TxN     int // total number of completed read transactions
+	OpenTxN int // number of currently open read transactions
+
 	TxStats TxStats // global, ongoing stats.
 }
 
-- 
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