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Comments about stabilize operation, track unsynced_writes correctly

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This commit is contained in:
Vitaliy Filippov
2019-11-11 02:53:19 +03:00
parent 8edb9e9d6f
commit d2d8d6e7fb
4 changed files with 69 additions and 40 deletions
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blockstore_stable.cpp
+38 -14
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@@ -1,5 +1,29 @@
#include "blockstore.h"
// Stabilize small write:
// 1) Copy data from the journal to the data device
// Sync it before writing metadata if we want to keep metadata consistent
// Overall it's optional because it can be replayed from the journal until
// it's cleared, and reads are also fulfilled from the journal
// 2) Increase version on the metadata device and sync it
// 3) Advance clean_db entry's version, clear previous journal entries
//
// This makes 1 4K small write+sync look like:
// 512b+4K (journal) + sync + 512b (journal) + sync + 4K (data) [+ sync?] + 512b (metadata) + sync.
// WA = 2.375. It's not the best, SSD FTL-like redirect-write with defragmentation
// could probably be lower even with defragmentation. But it's fixed and it's still
// better than in Ceph. :)
// Stabilize big write:
// 1) Copy metadata from the journal to the metadata device
// 2) Move dirty_db entry to clean_db and clear previous journal entries
//
// This makes 1 128K big write+sync look like:
// 128K (data) + sync + 512b (journal) + sync + 512b (journal) + sync + 512b (metadata) + sync.
// WA = 1.012. Very good :)
// AND We must do it in batches, for the sake of reduced fsync call count
int blockstore::dequeue_stable(blockstore_operation *op)
{
auto dirty_it = dirty_db.find((obj_ver_id){
@@ -61,6 +85,11 @@ int blockstore::dequeue_stable(blockstore_operation *op)
return 1;
}
int blockstore::continue_stable(blockstore_operation *op)
{
return 0;
}
void blockstore::handle_stable_event(ring_data_t *data, blockstore_operation *op)
{
if (data->res < 0)
@@ -72,21 +101,13 @@ void blockstore::handle_stable_event(ring_data_t *data, blockstore_operation *op
op->pending_ops--;
if (op->pending_ops == 0)
{
// Mark dirty_db entry as stable
// Mark all dirty_db entries up to op->version as stable
auto dirty_it = dirty_db.find((obj_ver_id){
.oid = op->oid,
.version = op->version,
});
if (dirty_it->second.state == ST_J_SYNCED)
{
// 1) Copy data from the journal to the data device
// 2) Increase version on the metadata device
// 3) Advance clean_db entry's version, clear previous journal entries
// This makes 1 4K small write+sync look like:
// 512b+4K (journal) + sync + 512b (journal) + sync + 512b (metadata) + 4K (data) + sync.
// WA = 2.375. It's not the best, SSD FTL-like redirect-write with defragmentation
// could probably be lower even with defragmentation. But it's fixed and it's still
// better than in Ceph. :)
dirty_it->second.state = ST_J_STABLE;
// Acknowledge op
op->retval = 0;
@@ -94,15 +115,18 @@ void blockstore::handle_stable_event(ring_data_t *data, blockstore_operation *op
}
else if (dirty_it->second.state == ST_D_META_SYNCED)
{
// 1) Copy metadata from the journal to the metadata device
// 2) Move dirty_db entry to clean_db and clear previous journal entries
// This makes 1 128K big write+sync look like:
// 128K (data) + sync + 512b (journal) + sync + 512b (journal) + sync + 512b (metadata) + sync.
// WA = 1.012. Very good :)
dirty_it->second.state = ST_D_STABLE;
// Acknowledge op
op->retval = 0;
op->callback(op);
}
else if (dirty_it->second.state == ST_J_STABLE)
{
}
else if (dirty_it->second.state == ST_D_STABLE)
{
}
}
}