Reformat journal index #7780
Reformat journal index #7780
Conversation
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@max-hoffman DOLT
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…t into max/streamline-journal-index
…t into max/streamline-journal-index
…t into max/streamline-journal-index
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#benchmark |
…t into max/streamline-journal-index
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@max-hoffman DOLT
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…t into max/streamline-journal-index
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#benchmark |
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@max-hoffman DOLT
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@max-hoffman DOLT
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@max-hoffman DOLT
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go/store/nbs/journal_index_record.go
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| recTag, err := rd.ReadByte() | ||
| if err != nil { | ||
| if errors.Is(err, io.EOF) { | ||
| return nil |
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We need to get the number of bytes we read after the last successfuly indexRecMeta callback back to the caller so that they can file.Seek() and file.Truncate() the output file to start at that point. Then we can start writing new records without causing a CRC failure in a later bootstrap.
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Same for the points where we return nil from ErrUnexpectedEOF down below.
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A bit of context that I was missing, the way this used to work was if anything went wrong we delete the index and exit process. The next startup loads all chunks into novel, and the next batch flush writes all chunks into a fresh index. Startup/clear/exit is the repeatable retry loop if anything goes wrong. Shitty for the next index flush, but it works.
The rewrite has different semantics that you pointed out. Now we are concerned with hanging index lookups after the last metadata record. I added a seek/truncate, which clears the handing lookups. We have to do an extra step where we add the hanging lookups back to the index for consistency. So I basically ignore most errors here, missing/malformed/io.EOF, we just truncate and rebuild. I think that should be equally repeatable, as long as there isn't a pathological loop where the index can't get a foothold for some reason.
Like one thing that is maybe a bit annoying in both versions is that we could rewrite the entire index, the server quits before writing a root value, and then next startup has to do it all over again. Reread all of the lookups, delete the index b/c no batch metadata, and then rebuilds the same index again. A 45 minute startup becoming like 3 hours would be annoying.
go/store/nbs/journal_index_record.go
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| batch = nil | ||
| batchCrc = 0 | ||
| default: | ||
| return fmt.Errorf("expected record to start with a chunk or metadata type tag") |
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In some ways different, in some ways...maybe not so different? Why an error here but ErrUnexpectedEOF is not one? If we there could be garbage beyond where we read...
go/store/nbs/journal_writer.go
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| if _, err = wr.index.Write(buf); err != nil { | ||
| return err | ||
| } | ||
| writeJournalIndexMeta(wr.indexWriter, root, wr.indexed, end, wr.batchCrc) |
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Update the comment here to be more accurate.
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@max-hoffman DOLT
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@max-hoffman DOLT
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@max-hoffman DOLT
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@max-hoffman DOLT
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@coffeegoddd DOLT
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Change the way we write journal index lookups. Each write appends a lookup to a
bufio.Writerthat lazily writes to disk. And after some increment we flush a CRC/root value record for consistency checking the index during bootstrap. This avoids big stalls for flushing a batch of index records. We also only write anaddr16now, because that's what we load into the default chunk address map.Databases with the older format will pay a one-time startup penalty to rewrite the journal index. In testing this appears to be 5-10% of the import time for the database.