diff --git a/.gitignore b/.gitignore
index 6cac9f6..094933e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,3 +6,4 @@ graphdump/
 __pycache__
 core
 _testtmp/
+*.pyc
diff --git a/ptnk/db.h b/ptnk/db.h
index 848cb9c..7e18154 100644
--- a/ptnk/db.h
+++ b/ptnk/db.h
@@ -8,8 +8,6 @@
 namespace ptnk
 {
 
-class TPIO;
-class TPIOTxSession;
 class TPIO;
 class TPIOTxSession;
 
diff --git a/ptnk/partitionedpageio.cpp b/ptnk/partitionedpageio.cpp
index ba1350e..d98dde5 100644
--- a/ptnk/partitionedpageio.cpp
+++ b/ptnk/partitionedpageio.cpp
@@ -20,6 +20,7 @@ namespace ptnk
 
 PartitionedPageIO::PartitionedPageIO(const char* dbprefix, ptnk_opts_t opts, int mode)
 :	m_mode(mode), m_opts(opts),
+	m_needInit(false),
     m_pgidLast(PGID_INVALID),
 	m_partidFirst(PTNK_PARTID_INVALID), m_partidLast(0),
 	m_helper(nullptr), m_isHelperInvoked(true)
diff --git a/ptnk/tpio.cpp b/ptnk/tpio.cpp
index 19ea3e3..377a577 100644
--- a/ptnk/tpio.cpp
+++ b/ptnk/tpio.cpp
@@ -48,6 +48,8 @@ TPIOTxSession::TPIOTxSession(TPIO* tpio, shared_ptr<ActiveOvr> aovr, unique_ptr<
 	m_aovr(move(aovr)),
 	m_lovr(move(lovr))
 {
+	tpio->registerTx(this);
+
 	m_lovr->attachExtra(unique_ptr<OvrExtra>(new OvrExtra));
 	m_oldlink = &reinterpret_cast<OvrExtra*>(m_lovr->getExtra())->oldlink;
 }
@@ -66,7 +68,7 @@ TPIOTxSession::OvrExtra::~OvrExtra()
 
 TPIOTxSession::~TPIOTxSession()
 {
-	/* NOP */
+	m_tpio->unregisterTx(this);
 }
 
 pair<Page, page_id_t>
@@ -216,6 +218,11 @@ TPIO::TPIO(shared_ptr<PageIO> backend, ptnk_opts_t opts)
 	m_bDuringRebase(false),
 	m_bDuringRefresh(false)
 {
+	for(size_t i = 0; i < NTXPOOL; ++ i)
+	{
+		m_txpool[i] = nullptr;
+	}
+
 	if(m_backend->needInit())
 	{
 		m_aovr = unique_ptr<ActiveOvr>(new ActiveOvr);
@@ -261,6 +268,34 @@ TPIO::newTransaction()
 	return unique_ptr<TPIOTxSession>(new TPIOTxSession(this, move(aovr), move(lovr)));
 }
 
+void
+TPIO::registerTx(TPIOTxSession* tx)
+{
+#ifdef PTNK_REGTX
+	for(size_t i = 0; i < NTXPOOL; ++ i)
+	{
+		if(!m_txpool[i] && PTNK_CAS(&m_txpool[i], 0, tx))
+		{
+			tx->m_regtxidx = i;
+			return;
+		}
+	}
+
+	PTNK_THROW_RUNTIME_ERR("out of session pool");
+#endif
+}
+
+void
+TPIO::unregisterTx(TPIOTxSession* tx)
+{
+#ifdef PTNK_REGTX
+	size_t i = tx->m_regtxidx;
+
+	PTNK_ASSERT(m_txpool[i] == tx);
+	m_txpool[i] = nullptr;
+#endif
+}
+
 void
 TPIO::syncDelayed(const Vpage_id_t& pagesModified)
 {
diff --git a/ptnk/tpio.h b/ptnk/tpio.h
index 1528e28..f180fbe 100644
--- a/ptnk/tpio.h
+++ b/ptnk/tpio.h
@@ -102,7 +102,7 @@ class TPIOTxSession : public PageIO
 
 	void addOvr(page_id_t pgidOrig, page_id_t pgidOvr)
 	{
-		m_lovr->addOvr(pgidOrig, pgidOvr);	
+		m_lovr->addOvr(pgidOrig, pgidOvr);
 	}
 
 	void loadStreak(BufferCRef bufStreak);
@@ -121,6 +121,7 @@ class TPIOTxSession : public PageIO
 	PagesOldLink* m_oldlink;
 	Vpage_id_t m_pagesModified;
 	TPIOStat m_stat;
+	size_t m_regtxidx;
 };
 inline
 std::ostream& operator<<(std::ostream& s, const TPIOTxSession& o)
@@ -193,6 +194,12 @@ class TPIO
 
 	std::mutex m_mtxRebase;
 	std::condition_variable m_condRebase;
+
+	static const size_t NTXPOOL = 256;
+	TPIOTxSession* m_txpool[NTXPOOL];
+public:
+	void registerTx(TPIOTxSession* tx);
+	void unregisterTx(TPIOTxSession* tx);
 };
 inline
 std::ostream& operator<<(std::ostream& s, const TPIO& o)