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Rewrite shared sstables only after entire CF is read

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Starting in commit 721f7d1d4f, we start "rewriting" a shared sstable (i.e.,
splitting it into individual shards) as soon as it is loaded in each shard.

However as discovered in issue #1366, this is too soon: Our compaction
process relies in several places that compaction is only done after all
the sstables of the same CF have been loaded. One example is that we
need to know the content of the other sstables to decide which tombstones
we can expire (this is issue #1366). Another example is that we use the
last generation number we are aware of to decide the number of the next
compaction output - and this is wrong before we saw all sstables.

So with this patch, while loading sstables we only make a list of shared
sstables which need to be rewritten - and the actual rewrite is only started
when we finish reading all the sstables for this CF. We need to do this in
two cases: reboot (when we load all the existing sstables we find on disk),
and nodetool referesh (when we import a set of new sstables).

Fixes #1366.

Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <1466344078-31290-1-git-send-email-nyh@scylladb.com>
This commit is contained in:
Nadav Har'El
2016-06-19 16:47:58 +03:00
committed by Avi Kivity
parent dde87e0b0e
commit faa45812b2
Notes: Avi Kivity 2016-06-19 17:20:18 +03:00 
backport: 1.1, 1.2
2 changed files with 24 additions and 2 deletions
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20
database.cc
View File

@@ -523,8 +523,11 @@ future<> column_family::load_sstable(sstables::sstable&& sstab, bool reset_level
// shard(s). Shared sstables cannot be deleted until all
// shards compacted them, so to reduce disk space usage we
// want to start splitting them now.
dblog.info("Splitting {} for shard", sst->get_filename());
_compaction_manager.submit_sstable_rewrite(this, sst);
// However, we need to delay this compaction until we read all
// the sstables belonging to this CF, because we need all of
// them to know which tombstones we can drop, and what
// generation number is free.
_sstables_need_rewrite.push_back(sst);
}
if (reset_level) {
// When loading a migrated sstable, set level to 0 because
@@ -539,6 +542,17 @@ future<> column_family::load_sstable(sstables::sstable&& sstab, bool reset_level
});
}
// load_sstable() wants to start rewriting sstables which are shared between
// several shards, but we can't start any compaction before all the sstables
// of this CF were loaded. So call this function to start rewrites, if any.
void column_family::start_rewrite() {
for (auto sst : _sstables_need_rewrite) {
dblog.info("Splitting {} for shard", sst->get_filename());
_compaction_manager.submit_sstable_rewrite(this, sst);
}
_sstables_need_rewrite.clear();
}
future<sstables::entry_descriptor> column_family::probe_file(sstring sstdir, sstring fname) {
using namespace sstables;
@@ -1065,6 +1079,7 @@ column_family::load_new_sstables(std::vector<sstables::entry_descriptor> new_tab
_schema->ks_name(), _schema->cf_name(), _config.datadir,
comps.generation, comps.version, comps.format), true);
}).then([this] {
start_rewrite();
// Drop entire cache for this column family because it may be populated
// with stale data.
return get_row_cache().clear();
@@ -1265,6 +1280,7 @@ future<> column_family::populate(sstring sstdir) {
});
});
}).then([this] {
start_rewrite();
// Make sure this is called even if CF is empty
mark_ready_for_writes();
});

6
database.hh
View File

@@ -343,6 +343,11 @@ private:
// have not been deleted yet, so must not GC any tombstones in other sstables
// that may delete data in these sstables:
std::vector<sstables::shared_sstable> _sstables_compacted_but_not_deleted;
// sstables that are shared between several shards so we want to rewrite
// them (split the data belonging to this shard to a separate sstable),
// but for correct compaction we need to start the compaction only after
// reading all sstables.
std::vector<sstables::shared_sstable> _sstables_need_rewrite;
// Control background fibers waiting for sstables to be deleted
seastar::gate _sstable_deletion_gate;
// There are situations in which we need to stop writing sstables. Flushers will take
@@ -372,6 +377,7 @@ private:
void add_sstable(sstables::sstable&& sstable);
void add_sstable(lw_shared_ptr<sstables::sstable> sstable);
future<> load_sstable(sstables::sstable&& sstab, bool reset_level = false);
void start_rewrite();
lw_shared_ptr<memtable> new_memtable();
lw_shared_ptr<memtable> new_streaming_memtable();
future<stop_iteration> try_flush_memtable_to_sstable(lw_shared_ptr<memtable> memt);