<p>This happens when <code>bitcoind</code> has processed a large amount of blocks in its dbcache but has not written them to disk before the process is exited.</p>

<p>See <a href="https://github.com/bitcoin/bitcoin/issues/11600#issuecomment-341733023" rel="nofollow noreferrer">here</a> for more details.</p>

CC BY-SA 3.0
2018-01-27T15:42:56.347Z
2018-01-27T15:42:56.347Z
mecampbellsoup
<p>When I start up bitcoin-qt, the screen says: <em>replaying blocks...0%</em>.</p>

<p>The <code>debug.log</code>'s tail contains messages</p>

<pre><code>2017-07-07 11:02:03 Rolling forward 0000000000000000010ac1a0c2f1003ae71457077a3a814a756f0b2b494e03d6 (472746)
2017-07-07 11:02:29 Rolling forward 00000000000000000124599553a07decfe065cc04f22a12fa5e5490e116242e5 (472747)
2017-07-07 11:02:45 Rolling forward 0000000000000000011da8f83f23856222693954dc38a0a203391cf51d3f1a52 (472748)
2017-07-07 11:03:04 Rolling forward 00000000000000000f382b835d682afbcbd2c248f85cbc4944bd8a3609455d3 (472749)
2017-07-07 11:03:17 Rolling forward 00000000000000000036c823c344ece1ca712257b7ed13a8fcea28f087f0a200 (472750)
2017-07-07 11:03:35 Rolling forward 000000000000000000048dbd7fa8b2732a2a1a22a5d8b9ebeaf938a96d52da41 (472751)
2017-07-07 11:03:53 Rolling forward 00000000000000000030d6c28b5cd8b7133c8a7fabc60f6ae65c646115e26237 (472752)
2017-07-07 11:04:16 Rolling forward 000000000000000000e4c2e323230fd6a266741f42aa965c86fae8205e2309ef (472753)
</code></pre>

<p>What does that mean? </p>

<p><strong>Edit</strong>
The <code>debug.log</code> also says:</p>

<pre><code>2017-07-07 10:50:35 LoadBlockIndexDB: transaction index disabled
</code></pre>

<p>I assume the transaction index should be enabled. Because it's not, this is the cause for the slow start up of bitcoin-qt.</p>

<p>If this is the case, how can I enable the transaction index?</p>

CC BY-SA 3.0
2018-01-27T15:40:46.217Z
I think it means it is re-validating those blocks to ensure it has the proper blockchain history. I'm not sure why this is necessary, however.
mecampbellsoup
CC BY-SA 3.0
2018-01-27T15:45:39.467Z
The transaction index is unrelated, and would only make things more slow.
Pieter Wuille
<blockchain><bitcoin-core>
What does "replaying blocks" mean?
René Nyffenegger
# What does "replaying blocks" mean?

(Asked by: username_0 on 2017-07-07)

When I start up bitcoin-qt, the screen says: replaying blocks...0%.
The debug.log's tail contains messages
2017-07-07 11:02:03 Rolling forward 0000000000000000010ac1a0c2f1003ae71457077a3a814a756f0b2b494e03d6 (472746)
2017-07-07 11:02:29 Rolling forward 00000000000000000124599553a07decfe065cc04f22a12fa5e5490e116242e5 (472747)
2017-07-07 11:02:45 Rolling forward 0000000000000000011da8f83f23856222693954dc38a0a203391cf51d3f1a52 (472748)
2017-07-07 11:03:04 Rolling forward 00000000000000000f382b835d682afbcbd2c248f85cbc4944bd8a3609455d3 (472749)
2017-07-07 11:03:17 Rolling forward 00000000000000000036c823c344ece1ca712257b7ed13a8fcea28f087f0a200 (472750)
2017-07-07 11:03:35 Rolling forward 000000000000000000048dbd7fa8b2732a2a1a22a5d8b9ebeaf938a96d52da41 (472751)
2017-07-07 11:03:53 Rolling forward 00000000000000000030d6c28b5cd8b7133c8a7fabc60f6ae65c646115e26237 (472752)
2017-07-07 11:04:16 Rolling forward 000000000000000000e4c2e323230fd6a266741f42aa965c86fae8205e2309ef (472753)

What does that mean? 
Edit
The debug.log also says:
2017-07-07 10:50:35 LoadBlockIndexDB: transaction index disabled

I assume the transaction index should be enabled. Because it's not, this is the cause for the slow start up of bitcoin-qt.
If this is the case, how can I enable the transaction index?

**Tags:** blockchain, bitcoin-core

> **Comments:**
> **username_1**: I think it means it is re-validating those blocks to ensure it has the proper blockchain history. I'm not sure why this is necessary, however.  
> **username_2**: The transaction index is unrelated, and would only make things more slow.  

---

## 1 answers

### Answer by username_1 on 2018-01-27. Score: 4 | Accepted answer

This happens when `bitcoind` has processed a large amount of blocks in its dbcache but has not written them to disk before the process is exited.

See [here](https://github.com/bitcoin/bitcoin/issues/11600#issuecomment-341733023) for more details.


---

