user19338: I'm using bitcoin core version 0.12.1 (To say precisely, I'm using addrindex patched bitcoin core by btcdrak)
I expected that mempool was maintained after restart bitcoind but that was deleted.
As far as I know that mempool is stored in chainstate/* directory as LevelDB data. 
I read this article. What is the database for?
Can you describe this is why and how can I avoid it. Sometimes, I have to restart my bitcoind for some reasons (like system maintanance). In that time I want to maintain the mempool data.
Getting mempool data from peers..? takes a long time.
getmempoolinfo before bitcoind restart
$ curl --user 'xxx:yyy' --data-binary '{"jsonrpc":"1.0","id":"curltext","method":"getmempoolinfo","params":[]}' -H 'content-type:text/plain;' http://127.0.0.1:8332
{"result":{"size":15350,"bytes":120107104,"usage":258574880,"maxmempool":300000000,"mempoolminfee":0.00000000},"error":null,"id":"curltext"}

getmempoolinfo after bitcoind restart
$ curl --user 'xxx:yyy' --data-binary '{"jsonrpc":"1.0","id":"curltext","method":"getmempoolinfo","params":[]}' -H 'content-type:text/plain;' http://127.0.0.1:8332
{"result":{"size":0,"bytes":0,"usage":0,"maxmempool":300000000,"mempoolminfee":0.00000000},"error":null,"id":"curltext"}


user208: So far, no released versions of Bitcoin Core exist that store the mempool on disk. That's why it's called the mempool; it's a pool of unconfirmed transactions kept in memory.
Version 0.14 is expected to introduce automatic dumping of the mempool to disk at shutdown.

19338: <p>I'm using bitcoin core version 0.12.1 (To say precisely, I'm using addrindex patched bitcoin core by btcdrak)</p>

<p>I expected that mempool was maintained after restart bitcoind but that was deleted.</p>

<p>As far as I know that mempool is stored in chainstate/* directory as LevelDB data. 
I read this article. <a href="https://bitcoin.stackexchange.com/questions/11104/what-is-the-database-for">What is the database for?</a></p>

<p>Can you describe this is why and how can I avoid it. Sometimes, I have to restart my bitcoind for some reasons (like system maintanance). In that time I want to maintain the mempool data.
Getting mempool data from peers..? takes a long time.</p>

<p>getmempoolinfo before bitcoind restart</p>

<pre><code>$ curl --user 'xxx:yyy' --data-binary '{"jsonrpc":"1.0","id":"curltext","method":"getmempoolinfo","params":[]}' -H 'content-type:text/plain;' http://127.0.0.1:8332
{"result":{"size":15350,"bytes":120107104,"usage":258574880,"maxmempool":300000000,"mempoolminfee":0.00000000},"error":null,"id":"curltext"}
</code></pre>

<p>getmempoolinfo after bitcoind restart</p>

<pre><code>$ curl --user 'xxx:yyy' --data-binary '{"jsonrpc":"1.0","id":"curltext","method":"getmempoolinfo","params":[]}' -H 'content-type:text/plain;' http://127.0.0.1:8332
{"result":{"size":0,"bytes":0,"usage":0,"maxmempool":300000000,"mempoolminfee":0.00000000},"error":null,"id":"curltext"}
</code></pre>
 208: <p>So far, no released versions of Bitcoin Core exist that store the mempool on disk. That's why it's called the <strong>mem</strong>pool; it's a pool of unconfirmed transactions kept in memory.</p>

<p>Version 0.14 is expected to introduce automatic dumping of the mempool to disk at shutdown.</p>
