core/rawdb, cmd, ethdb, eth: implement freezer tail deletion #23954
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We need to bump the database verison. |
rjl493456442
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Feb 16, 2022
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Now the freezer is fully compatible with the old version Geth. It's unnecessary to bump the database version. |
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…m#23954) * core/rawdb, cmd, ethdb, eth: implement freezer tail deletion * core/rawdb: address comments from martin and sina * core/rawdb: fixes cornercase in tail deletion * core/rawdb: separate metadata into a standalone file * core/rawdb: remove unused code * core/rawdb: add random test * core/rawdb: polish code * core/rawdb: fsync meta file before manipulating the index * core/rawdb: fix typo * core/rawdb: address comments
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…m#23954) * core/rawdb, cmd, ethdb, eth: implement freezer tail deletion * core/rawdb: address comments from martin and sina * core/rawdb: fixes cornercase in tail deletion * core/rawdb: separate metadata into a standalone file * core/rawdb: remove unused code * core/rawdb: add random test * core/rawdb: polish code * core/rawdb: fsync meta file before manipulating the index * core/rawdb: fix typo * core/rawdb: address comments
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…m#23954) * core/rawdb, cmd, ethdb, eth: implement freezer tail deletion * core/rawdb: address comments from martin and sina * core/rawdb: fixes cornercase in tail deletion * core/rawdb: separate metadata into a standalone file * core/rawdb: remove unused code * core/rawdb: add random test * core/rawdb: polish code * core/rawdb: fsync meta file before manipulating the index * core/rawdb: fix typo * core/rawdb: address comments
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This PR introduces the tail deletion of freezer.
File level deletion
The tail deletion is at file level by design. It means whenever data items at tail are deleted, they will not be removed from the file immediately. Instead they will be hidden until items in the tail data file are all deleted then the entire data file will be dropped.
Reasons
Performance
The reason for designing this lazy deletion mechanism is mainly for saving cost of updating index file. The lookup in freezer is using item id to calculate the relative position in index file, read the data position info from the index file and finally read the data from data file.
However in order to delete the tail items from the data file, all the remaining items in this data file must be shifted forward and all of them need to be re-indexed by modifying the corresponding position information in the index file. This action is super expensive. So deletion by file is a good choice in terms of avoiding re-index.
Atomicity
Another big reason for lazy deletion is it's easier to gain atomicity guarantee. The deletion procedure contains the mutation to index file and data file. These two mutations should be applied at the same time, or apply none of them.
In this design we only need to update the index file atomically. The de-referenced data file can be dropped any time, even after the crash. For sake of simplification, it's a big win.