Ethereum: Is there a way to reindex from disk but not start from blk0000.dat?

Reindexing Ethereum Blocks: Is it Possible to Start from a Different File?

As an experienced Bitcoin and Ethereum user, I recently encountered a frustrating issue during my daily sync process. My Ethereum wallet complained about downloading blocks from a corrupted file, which ultimately led me to investigate the possibility of reindexing from disk, but starting from a different file.

Error Message

Here is the error message that appeared on my terminal:

Error: File blk00217.dat or blk0000.dat not found

At first glance, it seemed like a simple problem with downloading complete blocks from disk. However, when I dug deeper into the problem, I discovered that Bitcoin-Qt was not only downloading full blocks, but also trying to start syncing from “blk0000.dat”, which is a corrupted file.

Understanding the Reindexing Process

To understand what’s going on, let’s dive into the basics of Ethereum block reindexing. When you run “eip155dumper” on your Bitcoin-Qt wallet (or any other Ethereum node), it creates a list of blocks that can be used to restore the blockchain to a previous state.

The reindexing process involves loading these blocks from disk and then rebuilding the blockchain. This is necessary because blocks are not stored in memory, but on disk, where the network updates them regularly.

Reindexing from disk, but not starting from a different file

Now let’s get to the heart of the matter: let’s start the reindexing from the file “blk0000.dat” instead of loading the full blocks from disk. To achieve this, you need to understand how Bitcoin-Qt loads and stores blocks on disk.

The file “blk0000.dat” is used as a “scratchpad” for loading new blocks during reindexing. It is not actual blockchain data stored on disk; rather, it is a temporary buffer containing the latest block from the network.

When Bitcoin-Qt starts reindexing, it loads this scratchpad file (or “blk0000.dat” in this case) and uses its contents to update the blockchain. The reindexed blocks are then written back to disk, restoring the blockchain to its previous state.

Workaround: Reindexing from a Different Scratchpad File

As I mentioned earlier, there is no direct way to start reindexing from a different Scratchpad file (i.e. “blk0000.dat”). However, you can achieve a similar result using a different approach:

• Load the blocks from disk using regular blk files (e.g. blk0010.dat, blk0020.dat, etc.).

• Create a new scratchpad file (e.g. scratchpad.dat) containing the latest block data.

• Use the scratched command to reindex from this scratchpad file.

You can use scratched as follows:

• Load the full blocks from disk using blk' files:blk0010.dat,blk0020.dat, etc.

• Create a new scratchpad file (e.g.scratchpad.dat) containing the latest block data:

scratch -o scratchpad.dat < blk0010.dat

• Run Ethereum-Qt in your wallet with the updated scratchpad file: eip155dumper`.

• Start the reindex from the Scratchpad file using reindex.

Conclusion

While it is not possible to start the reindex from another platform file, you can work around this limitation by using regular blk files and creating a new scratchpad file containing the latest block data. By following these steps, you should be able to achieve the desired result without having to download complete blocks from disk.

Remember that reindexing is an ongoing process, so check the status of your blockchain regularly and adjust your settings as needed. Have fun!