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Make backup write fully atomic. #664

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Merged
evoskuil merged 2 commits into from
Sep 11, 2025
Merged

Make backup write fully atomic. #664

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6b22363
Make backup write fully atomic.
evoskuil Sep 11, 2025
cea12a3
Purge temporary on restore, no purge on failed restore.
evoskuil Sep 11, 2025
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36 changes: 25 additions & 11 deletions include/bitcoin/database/impl/store.ipp
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Original file line number Diff line number Diff line change
Expand Up @@ -904,29 +904,40 @@ code CLASS::backup(const event_handler& handler, bool prune) NOEXCEPT

static const auto primary = configuration_.path / schema::dir::primary;
static const auto secondary = configuration_.path / schema::dir::secondary;
static const auto temporary = configuration_.path / schema::dir::temporary;

handler(event_t::archive_snapshot, table_t::store);

// Ensure existing and empty /temporary.
if ((ec = file::clear_directory_ex(temporary))) return ec;

// Ensure no /primary.
if (file::is_directory(primary))
{
// Delete /secondary, rename /primary to /secondary.
// Delete /secondary.
if ((ec = file::clear_directory_ex(secondary))) return ec;
if ((ec = file::remove_ex(secondary))) return ec;

// Rename /primary to /secondary (atomic).
if ((ec = file::rename_ex(primary, secondary))) return ec;
}

// Dump /heads memory maps to /primary.
if ((ec = file::clear_directory_ex(primary))) return ec;
ec = dump(primary, handler);
// Dump /heads memory maps to /temporary.
if ((ec = dump(temporary, handler)))
{
// Failed dump, clear temporary and rename secondary to primary.
if (file::clear_directory(temporary) && file::remove(temporary))
file::rename(secondary, primary);

// If failed clear primary and rename secondary to primary.
if (ec && file::clear_directory(primary) && file::remove(primary))
/* bool */ file::rename(secondary, primary);
// Return original fault.
return ec;
}

return ec;
// Rename /temporary to /primary (atomic).
return file::rename_ex(temporary, primary);
}

// Dump memory maps of /heads to new files in /primary.
// Dump memory maps of /heads to new files in /temporary.
// Heads are copied from RAM, not flushed to disk and copied as files.
TEMPLATE
code CLASS::dump(const path& folder,
Expand Down Expand Up @@ -1037,17 +1048,21 @@ code CLASS::restore(const event_handler& handler) NOEXCEPT
static const auto heads = configuration_.path / schema::dir::heads;
static const auto primary = configuration_.path / schema::dir::primary;
static const auto secondary = configuration_.path / schema::dir::secondary;
static const auto temporary = configuration_.path / schema::dir::temporary;

handler(event_t::recover_snapshot, table_t::store);

// Clean up any residual /temporary.
file::clear_directory(temporary);
file::remove(temporary);

if (file::is_directory(primary))
{
// Clear invalid /heads, recover from /primary, clone to /primary.
ec = file::clear_directory_ex(heads);
if (!ec) ec = file::remove_ex(heads);
if (!ec) ec = file::rename_ex(primary, heads);
if (!ec) ec = file::copy_directory_ex(heads, primary);
if (ec) /* bool */ file::remove_ex(primary);
}
else if (file::is_directory(secondary))
{
Expand All @@ -1056,7 +1071,6 @@ code CLASS::restore(const event_handler& handler) NOEXCEPT
if (!ec) ec = file::remove_ex(heads);
if (!ec) ec = file::rename_ex(secondary, heads);
if (!ec) ec = file::copy_directory_ex(heads, primary);
if (ec) /* bool */ file::remove_ex(secondary);
}
else
{
Expand Down
1 change: 1 addition & 0 deletions include/bitcoin/database/tables/names.hpp
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Expand Up @@ -31,6 +31,7 @@ namespace dir
constexpr auto heads = "heads";
constexpr auto primary = "primary";
constexpr auto secondary = "secondary";
constexpr auto temporary = "temporary";
}

namespace archive
Expand Down
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