MultiChain Developer Q&A - Recent questions tagged database

Database synchronization

Wed, 05 Feb 2020 16:26:53 +0000

It is mentioned within the white paper of multichain that

a future version of MultiChain will include a bridge between its blockchains and regular relational databases such as Oracle, SQL Server or MySQL

when can this version launch ? and could we use levelDB within the node to insert some data using regular database quries?

Connecting Multichain to Firebase Database and a mobile application

Fri, 21 Sep 2018 13:01:54 +0000

Hi there, anyone knows how:

1) to connect the firebase database with the multichain blockchain?

2) connect the blockchain with a mobile app (android and iOS)?

I managed to set up the blockchain via multichain but am clueless as to how the do up the connection. Would really appreciate if you could give detailed steps as to how to go about this matter. Thank you!

How does multichain deals with some unreliability problems that exist in LevelDB?

Thu, 16 Aug 2018 16:40:40 +0000

LevelDB has been categorized as unreliable due to it is prone to errors based on studies on previous versions. Apparently it can cause data corruption after systems crash or power failures. How does multichain deals with this type of bug when using LevelDB to store streams?

Can several Blockchains be merched into one new Blockchain?

Wed, 15 Aug 2018 15:05:48 +0000

Implementing "proof of origin" system for organic food industry

Wed, 13 Jun 2018 09:09:20 +0000

Hi,

We are trying to create concept of a "proof of origin" system based on SAP cloud platform and Multichain. The idea is to create distributed database but we wonder how to implement it. We have limited theoretical knowledge about blockchain technology. Do you know any real life example of such database we could analyze? Should we use data streams?

The overall goal is to create mobile app everyone can use to trail origin of different low-processed food (e.g. chicken, bag of sweet popatos) through some qr-code. What architecture we should chose to achieve such goal?

Is the levelDB database an attack vector when using streams?

Tue, 22 May 2018 18:38:23 +0000

In your response to this question, https://www.multichain.com/qa/9635/how-do-streams-work-under-the-hood, you stated that:

LevelDB stores indexes and transactions. But if the stream item data size is larger than 256 bytes, it is omitted from the LevelDB index, and replaced with a pointer to the data on disk (within the block). So large items are only stored once.

Does this mean that if someone were to find a way to edit data directly in levelDB, they could maliciously change the data that was stored in the database without having to change the blockchain, and mulitchain rpc calls would return this errant data?

For example, lets say I have a stream "myStream", and I publish to the key "foo" with the value "bar". An attacker decides the blockchain itself is too hard to attack, but they gain access to the levelDB instance, and replace the value for "foo" to be "attacker was here" instead of "bar". If I called "liststreamkeyitems foo". Would I get "bar", "attacker was here", or would there be some sort of error?

Thanks.

How do streams work under the hood?

Mon, 14 May 2018 22:13:21 +0000

As far as I know, blockchains do not provide a way to efficiently retrieve data. For example, if I'm looking for txs with a desired property (e.g. it has an output to a particular address), I simply have to traverse over each block and each tx in those blocks and fetch the matching txs.

However, Multichain seems to be providing a way to do the above task efficiently with streams if I understand correctly.How does it do that?

Here it says it indexes data like regular DBs. Where do these indexes stored? Are they stored off-chain, in local memory?

In general, how do streams achieve efficient retrieval of data?

How to exchange data between blockchain and database

Mon, 12 Mar 2018 07:27:16 +0000

I am working on a project wherein there are multiple systems that process the data and finally put it in a Azure SQL database. I have currently a blockchain with two nodes that is supposed to exchange (pull and push) data to this database in real time. Any ideas how this can be implemented adhering the best practices of using Multichain?

Reclaiming disk space

Thu, 22 Feb 2018 11:22:23 +0000

I understand that Multichain is an extension of Bitcoin, and section 7 of the bitcoin specification at http://www.bitcoin.com/bitcoin.pdf talks about reclaiming disk space from spent transactions. Does Multichain support this capability?

What can you store into Mutichain? Can it be Images, text and files?

Wed, 03 Jan 2018 17:15:43 +0000

I'm confused on what you can really save into Mutlichain. Is it just for money and finances or anything you want it to hold?

Multichain internal database

Sat, 09 Dec 2017 22:17:17 +0000

I understand bitcoin uses leveldb internally? What does Multichain use?

Thanks.

Regarding Custom Fields save in multichain Database

Thu, 02 Nov 2017 09:39:24 +0000

Hi,

I added custom fields in Multi-chain issues tab but i am not able to save my custom field value into database of multi chain. I checked database of multi-chain but they are in .dat files. How can i achieve these now.

thanks.

Can this platform be used to store other information too ?

Sun, 01 Oct 2017 13:00:49 +0000

Can this platform be used to store some other information too apart from using blockchains only as a source for cryptocurrency ?

is there any tutorial available for creating a database?

Thu, 21 Sep 2017 10:56:19 +0000

Is it possible to use MultiChain as database to store large XML in?

Thu, 14 Sep 2017 12:27:23 +0000

I'm looking for a blockchain solution to replace a centralized database solution. It will function as an exchange between multiple parties for the xml data.

I saw its possible to exchange data between parties using the MultiChain streams. Is this something I can use with storing big(0-10mb files) XML in the blockchain?

Where are the hashes stored

Mon, 10 Jul 2017 16:04:24 +0000

The transaction that i do from one node to other are blocks. So where do i see these blocks or hashes actually getting chained ? Is there some file or so

Also I am doing a transaction from no where,I create an asset named dollar and transfer any amount to other node, how do i link to a database and check if there is any is any fund to transfer to other node and it gets reflected in the database where the amount is debited and credited from one account to other in form of data ?

Could provide with the help

Performance measurement for Multichain streams

Sun, 15 Jan 2017 14:08:30 +0000

Hi,

Do you have any performance measurement for the use of Multichain stream as a nosql database?

R.

How do I automatically reject transactions with specific metadata?

Wed, 29 Jun 2016 11:20:48 +0000

I'm trying to build an application using MultiChain, using it as a append-only archive, as described here. How can I prevent nodes from adding entries with certain metadata? How can I make other nodes reject all transactions containing specific metadata? At least majority of the nodes run same code for validation, so rejecting doesn't create consensus problems.

Local DB vs Central DB in private blockchain

Mon, 16 May 2016 06:37:20 +0000

Hi,

We are working on a Letter of Credit(LC) POC on multichain. As part of our setup, we are having 4 nodes on private blockchain - Exporter,Importer and their corresponding banks. Now we want to build a trade/business view out of the transactions which happen on the blockchain for these entities as part of LC cycle. For that we are trying to capture the transactions happening on the blockchain in a database by parsing every block and inputting the LC related transactions in the database.

Now our question is should we do this at all nodes or can we keep a central database and through access control we manage that the nodes which are actually involved in the transaction get a full view otherwise, they only see a partial view of the transaction or don't see the transaction at all?

What would be your recommendation on the database setup?

Thanks.

Stores of data not financial transactions?

Tue, 03 May 2016 14:05:56 +0000

Hey all,

I have experience using and developing on multichain with making my own explorer before the official one was live.

My new project wants to implement a blockchain to store messages/data/files, then attribute meta-data to the record for easy searching on a front-end. I assume I can do this by just converting the raw strings to hexadecimal. What about perhaps a .pdf or .docx? Can this be attached/encoded then sent as a transaction to the network?

This chain will have free transactions.

To achieve meta information on transactions, is it possible to attach the data in a JSON object with the actual file/text in a sub-object?

Corrupted block database detected.

Tue, 22 Mar 2016 09:20:40 +0000

In the scenario where we have 3 nodes, lets say we made node 1 first then node 2 then 3. Nodes 2 and 3 are replicas of 1. If we insert assets from node 2 into the wallet of node 1 the assets are generated at a
high rate. At one point during "insert from 2 to 1" speed at which assets were being inserted dropped significantly (it seems that node 1 was choking) then node 1 crashed and speed of inserting got back to high.

when i tried to restart node 1 i got an error saying :

: Corrupted block database detected.

Please restart multichaind with reindex=1.

i assume this was probably a hardware glitch or something but i wanted to ask you what can cause this error and also what causes the "choke" that caused node 1 to crash in the first place? Should we add a small sleeep(5s) every 100 sec or so to avoid this or something?

debug log:

2016-03-22 08:55:48 MultiChain version build 1.0 alpha 18 protocol 10005 (2016-03-13 08:58:54 +0200)
2016-03-22 08:55:48 Using OpenSSL version OpenSSL 1.0.1h 5 Jun 2014
2016-03-22 08:55:48 Using BerkeleyDB version Berkeley DB 4.8.30: (April 9, 2010)
2016-03-22 08:55:48 Default data directory /home/sloba/.multichain/theone
2016-03-22 08:55:48 Using data directory /home/sloba/.multichain/theone
2016-03-22 08:55:48 Using config file /home/sloba/.multichain/theone/theone.conf
2016-03-22 08:55:48 Using at most 125 connections (1024 file descriptors available)
2016-03-22 08:55:48 Using 4 threads for script verification
2016-03-22 08:55:48 Using wallet wallet.dat
2016-03-22 08:55:48 init message: Verifying wallet...
2016-03-22 08:55:48 CDBEnv::Open : LogDir=/home/sloba/.multichain/theone/database ErrorFile=/home/sloba/.multichain/theone/db.log
2016-03-22 08:55:49 init message: Initializing multichain...
2016-03-22 08:55:50 nFileVersion = 100000
2016-03-22 08:55:50 Keys: 3 plaintext, 0 encrypted, 3 w/ metadata, 3 total
2016-03-22 08:55:50 mchn: Parameter set is valid - initializing blockchain parameters...
2016-03-22 08:55:50 Binding RPC on address ::1 port 7724 (IPv4+IPv6 bind any: 0)
2016-03-22 08:55:50 Binding RPC on address 127.0.0.1 port 7724 (IPv4+IPv6 bind any: 0)
2016-03-22 08:55:50 Bound to [::]:7725
2016-03-22 08:55:50 Bound to 0.0.0.0:7725
2016-03-22 08:55:50 init message: Loading block index...
2016-03-22 08:55:50 Opening LevelDB in /home/sloba/.multichain/theone/blocks/index
2016-03-22 08:55:50 Opened LevelDB successfully
2016-03-22 08:55:50 Opening LevelDB in /home/sloba/.multichain/theone/chainstate
2016-03-22 08:55:50 Opened LevelDB successfully
2016-03-22 08:55:50 LoadBlockIndexDB: last block file = 0
2016-03-22 08:55:50 LoadBlockIndexDB: last block file info: CBlockFileInfo(blocks=1404, size=16787062, heights=0...1396, time=2016-03-21...2016-03-22)
2016-03-22 08:55:50 Checking all blk files are present...
2016-03-22 08:55:50 LoadBlockIndexDB(): transaction index enabled
2016-03-22 08:55:51 LoadBlockIndexDB(): hashBestChain=00004bfc0db5821879c2b167ba2c6cefe8c18320b5eabb9043d2032dcf178dcb height=1396 date=2016-03-22 08:20:46 progress=1.000000
2016-03-22 08:55:51 init message: Verifying blocks...
2016-03-22 08:55:51 Verifying last 288 blocks at level 3
2016-03-22 08:55:51 ERROR: VerifyDB() : *** found bad permission data at 1396, hash=00004bfc0db5821879c2b167ba2c6cefe8c18320b5eabb9043d2032dcf178dcb

2016-03-22 08:55:51 : Corrupted block database detected.

Please restart multichaind with reindex=1.
2016-03-22 08:55:51 Aborted block database rebuild. Exiting.
2016-03-22 08:55:51 Shutdown: In progress...
2016-03-22 08:55:51 StopNode()
2016-03-22 08:55:51 Node stopped
2016-03-22 08:55:51 Shutdown: done
2016-03-22 08:55:51 CDBEnv::EnvShutdown : Error 22 shutting down database environment: Invalid argument

handshakelocal parameter is ignored

Thu, 17 Mar 2016 09:18:06 +0000

Greetings,

Unfortunately the only admin node's DB in my network became corrupt. I have tried to reindex, which did not help, so I have followed your instructions to:

delete everything but the multichain.conf and wallet.dat
connected to an other node to replicate the data
tried to start up the local installation with the -handshakelocal=<address> parameter

The address is the main address I had on the admin node and the only with admin permission. I tried to define the parameter with and without ' ', tried to put it into the multichain.conf, but whenever I try to start the blockchain, it insists on the newly created address:

$ multichaind zolichain1 --handshakelocal=1TFvWaHMkbBUnfGyXJZgtxCmMHmqMytiPz24Lm

MultiChain Core Daemon build 1.0 alpha 18 protocol 10005

Retrieving blockchain parameters from the seed node 10.0.1.152:8347 ...

Blockchain successfully initialized.

Please ask blockchain admin or user having activate permission to let you connect and/or transact:

multichain-cli zolichain1 grant 1UscW9kQinoKp9GncpybXCMPyyZK6m8zr3S8cd connect

multichain-cli zolichain1 grant 1UscW9kQinoKp9GncpybXCMPyyZK6m8zr3S8cd connect,send,receive

What do I do wrong here?

Many thanks in advance,

Kind Regards,

Zoli

Setup a multichain to contain arbitrary data

Thu, 25 Feb 2016 19:50:35 +0000

I'm starting a research project looking at storing small amounts i.e. up to 100k of arbitrary data (encrypted private data) within a blockchain and think multichain could be a good API choice. I guess follwing in the spirit of Namecoin but with arbitrary binary data blobs not DNS records. But I don't see how this could be achieved in the multichain blocks at least from the simple examples posted on the multichain.com site.

a) Is this actually possible with multichain?

b) If so is there an example anywhere or can someone point me in the right direction?

Thanks!

Storage of data

Tue, 23 Feb 2016 19:09:15 +0000

I've seen mention of 8MB transactions being stored, how is this effected? Is the OP_RETURN the only way to store data in the chain?

Thanks again,

Rua

MultiChain data storage limitations/questions.

Mon, 22 Feb 2016 20:23:47 +0000

Hello,

I am currently starting a project and am hoping that MultiChain will be fit for our uses. I want to be able to store a file in the chain (ranging in size from approx 3MB to 7MB) so as a locally stored copy of the file can be compared to the data that is stored within the blockchain to ensure that this indeed is the file in question and that it has been in no way altered since it was created.

I have done quite a bit of reading through this website and have seen how metadata can be stored as part of the OP_RETURN part of the transaction however the limit on this is approx 125KB. Elsewhere on this forum it has been stated that the maximum size one can encode is 8MB. Am I missing something here? Is there a way to encode more data than 1048576 in a transaction? If the transaction size can be set to 10000000 what happens to all this other available space and is there an api call to manipulate this? My current chain has the following params configured:

only-accept-std-txs = true              # Only standard transactions are accepted to mempool and relayed.
max-std-tx-size = 3000000               # Maximal size of standard transaction. (1024 - 10000000)
max-std-op-return-size = 1048576        # Maximal size of the data after OP_RETURN. (0 - 1048576)
max-std-op-drops-count = 5              # Maximal amount of OP_DROPs in the script. (0 - 100)
max-std-op-drop-size = 64               # Maximal size of the script element followed by OP_DROPs. (0 - 32768)

I have been currently using the sendwithmetadatafrom api, along with listtransactions and getwallettransaction to query the transactions from the other node. Could you elaborate a bit more on these limits of file size etc, and point me in the right direction as to how to best proceed.

On another related issue, I wrote a simple shell script which was basically a for loop to do 10000 of these transactions (sendwithmetadatafrom with the addresses and approx 100KB of metadata) however it appears to have broken the chain somewhat. 490 of these transactions completed and the rest I am not quite sure what has happened to them. I was thinking that perhaps with the 15secondconsensus time that some transactions got bottlenecked and were parsed wrong, however while I can see the send transactions from the first node they are not available for query on the second node? Am I on the right track here or do you have any information on what would be the best way to effectively "load" a chain full of transactions.

I am new to MultiChain and any help you can give me here will be greatly appreciated.

Thanks in advance,

Rua

Can multichain be used to save structured data or any data other than transactions?

Thu, 11 Feb 2016 13:30:07 +0000

Can multichain be used to save structured data or any data other than transactions? We are looking at a use case where some existing data which resides in database can be made available on blockchain.

Can multichain be used as data store instead of a database table? If yes, please point to the relevant documentation.

MultiChain as distributed MVCC

Sat, 23 Jan 2016 09:41:04 +0000

Basically, I want to put an arbitrary database on a blockchain (let's assume for argument's sake that I'm not trying to squeeze a silly amount of data into every transaction).

In this blog post, http://www.multichain.com/blog/2015/07/bitcoin-vs-blockchain-debate/, Gideon refers to using a blockchain as a form of distributed multiversion concurrency control for a database.

How would I go about using MultiChain to do this? My initial attempts have been to change a row of a table into a stringified JSON object, to be sent as transactional metadata. This feels hackish though. Is there a better way?

MultiChain as a distributed database

Sun, 06 Dec 2015 08:29:46 +0000

Hi,

I'd like to use MultiChain as a distributed database to store a variety of configuration and status information of a bunch of serves to avoid a single point of failure or setting up a database servers on each of the nodes with multi-master setup.

How would you configure MultiChain in this case?

Why use a blockchain?

Fri, 21 Aug 2015 12:42:13 +0000

I have a read articles on the why a distributed ledger is good and better that a normal DB? Today with the cloud and new DBs the flexibility in DB storage is pretty good. Any strong reason why the blockchain distributed ledger is much better than available traditional ledgers?