[FLASH-470/516] DM learner read and check gc safe point (pingcap#249)

* Do learner read before reading data from StorageDeltaMerge
* Check GC safe point

dbms/src/Debug/dbgFuncRegion.cpp

@@ -127,7 +127,7 @@ void dbgFuncRegionSnapshotWithData(Context & context, const ASTs & args, DBGInvo
     for (auto it = args_begin; it != args_end; it += len)
     {
         HandleID handle_id = (HandleID)safeGet<UInt64>(typeid_cast<const ASTLiteral &>(*it[0]).value);
-        Timestamp tso = safeGet<UInt64>(typeid_cast<const ASTLiteral &>(*it[1]).value);
+        Timestamp tso = (Timestamp)safeGet<UInt64>(typeid_cast<const ASTLiteral &>(*it[1]).value);
         UInt8 del = (UInt8)safeGet<UInt64>(typeid_cast<const ASTLiteral &>(*it[2]).value);
         {
             std::vector<Field> fields;

dbms/src/Storages/DeltaMerge/tests/gtest_dm_storage_delta_merge.cpp

@@ -185,8 +185,13 @@ try
         ASTPtr astptr(new ASTIdentifier("t", ASTIdentifier::Kind::Table));
         astptr->children.emplace_back(new ASTIdentifier("col1"));
 
-        storage           = StorageDeltaMerge::create(
-            ".", /* db_name= */ "default", /* name= */ "t", std::nullopt, ColumnsDescription{names_and_types_list}, astptr, DMTestEnv::getContext());
+        storage = StorageDeltaMerge::create(".",
+                                            /* db_name= */ "default",
+                                            /* name= */ "t",
+                                            std::nullopt,
+                                            ColumnsDescription{names_and_types_list},
+                                            astptr,
+                                            DMTestEnv::getContext());
         storage->startup();
     }
 
@@ -201,10 +206,14 @@ try
     }
 
     // get read stream from DeltaMergeStorage
+    Context &                  global_ctx = DMTestEnv::getContext();
     QueryProcessingStage::Enum stage2;
     SelectQueryInfo            query_info;
-    query_info.query        = std::make_shared<ASTSelectQuery>();
-    BlockInputStreamPtr dms = storage->read(column_names, query_info, DMTestEnv::getContext(), stage2, 8192, 1)[0];
+    query_info.query                          = std::make_shared<ASTSelectQuery>();
+    query_info.mvcc_query_info                = std::make_unique<MvccQueryInfo>();
+    query_info.mvcc_query_info->resolve_locks = global_ctx.getSettingsRef().resolve_locks;
+    query_info.mvcc_query_info->read_tso      = global_ctx.getSettingsRef().read_tso;
+    BlockInputStreamPtr dms                   = storage->read(column_names, query_info, global_ctx, stage2, 8192, 1)[0];
     dms->readPrefix();
 
     size_t num_rows_read = 0;

dbms/src/Storages/StorageDeltaMerge.cpp

@@ -20,6 +20,9 @@
 #include <Parsers/ASTInsertQuery.h>
 #include <Parsers/ASTLiteral.h>
 #include <Parsers/ASTSelectQuery.h>
+#include <Storages/Transaction/KVStore.h>
+#include <Storages/Transaction/Region.h>
+#include <Storages/Transaction/RegionException.h>
 #include <Storages/Transaction/TMTContext.h>
 #include <Storages/Transaction/TypeMapping.h>
 
@@ -238,6 +241,110 @@ BlockOutputStreamPtr StorageDeltaMerge::write(const ASTPtr & query, const Settin
 }
 
 
+namespace
+{
+
+void throwRetryRegion(const MvccQueryInfo::RegionsQueryInfo & regions_info)
+{
+    std::vector<RegionID> region_ids;
+    region_ids.reserve(regions_info.size());
+    for (const auto & info : regions_info)
+        region_ids.push_back(info.region_id);
+    throw RegionException(region_ids);
+}
+
+inline void doLearnerRead(const TiDB::TableID table_id,         //
+    const MvccQueryInfo::RegionsQueryInfo & regions_query_info, //
+    TMTContext & tmt, Poco::Logger * log)
+{
+    assert(log != nullptr);
+
+    MvccQueryInfo::RegionsQueryInfo regions_info;
+    if (!regions_query_info.empty())
+    {
+        regions_info = regions_query_info;
+    }
+    else
+    {
+        // Only for test, because regions_query_info should never be empty if query is from TiDB or TiSpark.
+        auto regions = tmt.getRegionTable().getRegionsByTable(table_id);
+        regions_info.reserve(regions.size());
+        for (const auto & [id, region] : regions)
+        {
+            if (region == nullptr)
+                continue;
+            regions_info.emplace_back(RegionQueryInfo{id, region->version(), region->confVer(), {0, 0}});
+        }
+    }
+
+    KVStorePtr & kvstore = tmt.getKVStore();
+    RegionMap kvstore_region;
+    // check region is not null and store region map.
+    for (const auto & info : regions_info)
+    {
+        auto region = kvstore->getRegion(info.region_id);
+        if (region == nullptr)
+        {
+            LOG_WARNING(log, "[region " << info.region_id << "] is not found in KVStore, try again");
+            throwRetryRegion(regions_info);
+        }
+        kvstore_region.emplace(info.region_id, std::move(region));
+    }
+    // make sure regions are not duplicated.
+    if (unlikely(kvstore_region.size() != regions_info.size()))
+        throw Exception("Duplicate region id", ErrorCodes::LOGICAL_ERROR);
+
+    auto start_time = Clock::now();
+    /// Blocking learner read. Note that learner read must be performed ahead of data read,
+    /// otherwise the desired index will be blocked by the lock of data read.
+    for (auto && [region_id, region] : kvstore_region)
+    {
+        (void)region_id;
+        region->waitIndex(region->learnerRead());
+    }
+    auto end_time = Clock::now();
+    LOG_DEBUG(log,
+        "[Learner Read] wait index cost " << std::chrono::duration_cast<std::chrono::milliseconds>(end_time - start_time).count() << " ms");
+
+    // After raft index is satisfied, we flush region to StorageDeltaMerge so that we can read all data
+    start_time = Clock::now();
+    std::set<RegionID> regions_flushing_in_bg_threads;
+    auto & region_table = tmt.getRegionTable();
+    for (auto && [region_id, region] : kvstore_region)
+    {
+        (void)region;
+        bool is_flushed = region_table.tryFlushRegion(region_id, table_id, false);
+        // If region is flushing by other bg threads, we should mark those regions to wait.
+        if (!is_flushed)
+        {
+            regions_flushing_in_bg_threads.insert(region_id);
+            LOG_DEBUG(log, "[Learner Read] region " << region_id << " is flushing by other thread.");
+        }
+    }
+    end_time = Clock::now();
+    LOG_DEBUG(log,
+        "[Learner Read] flush " << kvstore_region.size() - regions_flushing_in_bg_threads.size() << " regions of " << kvstore_region.size()
+                                << " to StorageDeltaMerge cost "
+                                << std::chrono::duration_cast<std::chrono::milliseconds>(end_time - start_time).count() << " ms");
+
+    // Maybe there is some data not flush to store yet, we should wait till all regions is flushed.
+    if (!regions_flushing_in_bg_threads.empty())
+    {
+        start_time = Clock::now();
+        for (const auto & region_id : regions_flushing_in_bg_threads)
+        {
+            region_table.waitTillRegionFlushed(region_id);
+        }
+        end_time = Clock::now();
+        LOG_DEBUG(log,
+            "[Learner Read] wait bg flush " << regions_flushing_in_bg_threads.size() << " regions to StorageDeltaMerge cost "
+                                            << std::chrono::duration_cast<std::chrono::milliseconds>(end_time - start_time).count()
+                                            << " ms");
+    }
+}
+
+} // namespace
+
 BlockInputStreams StorageDeltaMerge::read( //
     const Names & column_names,
     const SelectQueryInfo & query_info,
@@ -279,11 +386,30 @@ BlockInputStreams StorageDeltaMerge::read( //
         return store->readRaw(context, context.getSettingsRef(), to_read, num_streams);
     else
     {
-        // read with specify tso
-        UInt64 max_version = DEFAULT_MAX_READ_TSO;
-        if (query_info.mvcc_query_info)
-            max_version = query_info.mvcc_query_info->read_tso;
-        return store->read(context, context.getSettingsRef(), to_read, ranges, num_streams, max_version, max_block_size);
+        if (unlikely(!query_info.mvcc_query_info))
+            throw Exception("mvcc query info is null", ErrorCodes::LOGICAL_ERROR);
+
+        TMTContext & tmt = context.getTMTContext();
+        if (unlikely(!tmt.isInitialized()))
+            throw Exception("TMTContext is not initialized", ErrorCodes::LOGICAL_ERROR);
+
+        const auto & mvcc_query_info = *query_info.mvcc_query_info;
+        // Read with specify tso, check if tso is smaller than TiDB GcSafePoint
+        const auto safe_point = tmt.getPDClient()->getGCSafePoint();
+        if (mvcc_query_info.read_tso < safe_point)
+            throw Exception("query id: " + context.getCurrentQueryId() + ", read tso: " + toString(mvcc_query_info.read_tso)
+                    + " is smaller than tidb gc safe point: " + toString(safe_point),
+                ErrorCodes::LOGICAL_ERROR);
+
+        // With `no_kvstore` is true, we do not do learner read
+        if (likely(!select_query.no_kvstore))
+        {
+            /// Learner read.
+            doLearnerRead(tidb_table_info.id, mvcc_query_info.regions_query_info, tmt, log);
+        }
+
+        return store->read(
+            context, context.getSettingsRef(), to_read, ranges, num_streams, /*max_version=*/mvcc_query_info.read_tso, max_block_size);
     }
 }
 

dbms/src/Storages/Transaction/RegionTable.cpp

@@ -361,7 +361,7 @@ void RegionTable::tryFlushRegion(RegionID region_id)
         tryFlushRegion(region_id, table_id, false);
 }
 
-void RegionTable::tryFlushRegion(RegionID region_id, TableID table_id, const bool try_persist)
+bool RegionTable::tryFlushRegion(RegionID region_id, TableID table_id, const bool try_persist)
 {
     const auto func_update_region = [&](std::function<bool(InternalRegion &)> && callback) -> bool {
         std::lock_guard<std::mutex> lock(mutex);
@@ -397,7 +397,7 @@ void RegionTable::tryFlushRegion(RegionID region_id, TableID table_id, const boo
     });
 
     if (!status)
-        return;
+        return false;
 
     std::exception_ptr first_exception;
 
@@ -420,14 +420,16 @@ void RegionTable::tryFlushRegion(RegionID region_id, TableID table_id, const boo
         if (cache_bytes)
             dirty_regions.insert(region_id);
         else
-            dirty_regions.erase(region_id);
+            clearDirtyFlag(region_id);
 
         internal_region.last_flush_time = Clock::now();
         return true;
     });
 
     if (first_exception)
         std::rethrow_exception(first_exception);
+
+    return true;
 }
 
 bool RegionTable::tryFlushRegions()
@@ -466,7 +468,7 @@ bool RegionTable::tryFlushRegions()
             if (shouldFlush(region))
             {
                 to_flush = DataToFlush{table_id, region.region_id, true};
-                dirty_regions.erase(region.region_id);
+                clearDirtyFlag(region.region_id);
                 return true;
             }
             return false;
@@ -481,6 +483,19 @@ bool RegionTable::tryFlushRegions()
     return true;
 }
 
+void RegionTable::clearDirtyFlag(RegionID region_id)
+{
+    std::lock_guard lock(dirty_regions_mutex);
+    dirty_regions.erase(region_id);
+    dirty_regions_cv.notify_all();
+}
+
+void RegionTable::waitTillRegionFlushed(const RegionID region_id)
+{
+    std::unique_lock lock(dirty_regions_mutex);
+    dirty_regions_cv.wait(lock, [this, region_id]{ return dirty_regions.count(region_id) == 0;});
+}
+
 void RegionTable::handleInternalRegionsByTable(const TableID table_id, std::function<void(const InternalRegions &)> && callback) const
 {
     std::lock_guard<std::mutex> lock(mutex);

dbms/src/Storages/Transaction/RegionTable.h

@@ -1,6 +1,8 @@
 #pragma once
 
+#include <condition_variable>
 #include <functional>
+#include <mutex>
 #include <optional>
 #include <vector>
 
@@ -145,7 +147,9 @@ class RegionTable : private boost::noncopyable
     bool tryFlushRegions();
 
     void tryFlushRegion(RegionID region_id);
-    void tryFlushRegion(RegionID region_id, TableID table_id, const bool try_persist);
+    bool tryFlushRegion(RegionID region_id, TableID table_id, const bool try_persist);
+
+    void waitTillRegionFlushed(RegionID region_id);
 
     void handleInternalRegionsByTable(const TableID table_id, std::function<void(const InternalRegions &)> && callback) const;
     std::vector<std::pair<RegionID, RegionPtr>> getRegionsByTable(const TableID table_id) const;
@@ -191,6 +195,8 @@ class RegionTable : private boost::noncopyable
     void doShrinkRegionRange(const Region & region);
     void doUpdateRegion(const Region & region, TableID table_id);
 
+    void clearDirtyFlag(RegionID region_id);
+
     struct TableOptimizeChecker
     {
         std::mutex mutex;
@@ -203,6 +209,8 @@ class RegionTable : private boost::noncopyable
     TableMap tables;
     RegionInfoMap regions;
     std::unordered_set<RegionID> dirty_regions;
+    std::mutex dirty_regions_mutex;
+    std::condition_variable dirty_regions_cv;
     std::unordered_set<TableID> table_to_optimize;
 
     FlushThresholds flush_thresholds;

dbms/src/test_utils/TiflashTestBasic.h

@@ -1,8 +1,10 @@
 #pragma once
 
-#include <Interpreters/Context.h>
 #include <gtest/gtest.h>
 
+#include <Interpreters/Context.h>
+#include <Storages/Transaction/TMTContext.h>
+
 namespace DB
 {
 namespace tests
@@ -20,7 +22,8 @@ class TiFlashTestEnv
         }
         catch (Exception & e)
         {
-            context.createTMTContext({}, "", "", {"default"}, "./__tmp_data/kvstore", "./__tmp_data/regmap", TiDB::StorageEngine::TMT);
+            context.createTMTContext({}, "", "", {"default"}, "./__tmp_data/kvstore", TiDB::StorageEngine::TMT);
+            context.getTMTContext().restore();
         }
         context.getSettingsRef() = settings;
         return context;

tests/delta-merge-test/raft/read_with_specify_tso.test

@@ -17,9 +17,9 @@
 => DBGInvoke __region_snapshot_data(
     default, test_dm,
     4, 0, 1000,
-    2, 0, 0, 11,
-    1, 3, 0, 13,
-    3, 4, 0, 0
+    2, 20000000, 0,     11,
+    1, 20000003, 0,     13,
+    3, 20000004, 0,     0
     )
 => DBGInvoke __try_flush_region(4)
 => select * from default.test_dm
@@ -31,11 +31,11 @@
 
 ## raft_insert_row_full(db_name, tbl_name, region_id,   handle_id, tso, del, val1, val2, ...)
 ## upset rowid==3 with col_1 == 10086
-=> DBGInvoke __raft_insert_row_full(default, test_dm, 4,   3, 5, 0, 10086)
+=> DBGInvoke __raft_insert_row_full(default, test_dm, 4,   3, 20000005, 0, 10086)
 ## del rowid == 2
-=> DBGInvoke __raft_insert_row_full(default, test_dm, 4,   2, 5, 1, 0)
+=> DBGInvoke __raft_insert_row_full(default, test_dm, 4,   2, 20000005, 1, 0)
 ## insert rowid==4
-=> DBGInvoke __raft_insert_row_full(default, test_dm, 4,   4, 5, 0, 1234)
+=> DBGInvoke __raft_insert_row_full(default, test_dm, 4,   4, 20000005, 0, 1234)
 => DBGInvoke __try_flush_region(4)
 => select (*) from default.test_dm
 ┌─col_1─┬─_tidb_rowid─┐
@@ -45,32 +45,32 @@
 └───────┴─────────────┘
 
 ## read with specify tso
-=> select * from default.test_dm " --read_tso "0
+=> select * from default.test_dm " --read_tso "20000000
 ┌─col_1─┬─_tidb_rowid─┐
 │    11 │           2 │
 └───────┴─────────────┘
 
-=> select * from default.test_dm " --read_tso "3
+=> select * from default.test_dm " --read_tso "20000003
 ┌─col_1─┬─_tidb_rowid─┐
 │    13 │           1 │
 │    11 │           2 │
 └───────┴─────────────┘
 
-=> select * from default.test_dm " --read_tso "4
+=> select * from default.test_dm " --read_tso "20000004
 ┌─col_1─┬─_tidb_rowid─┐
 │    13 │           1 │
 │    11 │           2 │
 │     0 │           3 │
 └───────┴─────────────┘
 
-=> select * from default.test_dm " --read_tso "5
+=> select * from default.test_dm " --read_tso "20000005
 ┌─col_1─┬─_tidb_rowid─┐
 │    13 │           1 │
 │ 10086 │           3 │
 │  1234 │           4 │
 └───────┴─────────────┘
 
-=> select * from default.test_dm " --read_tso "100000
+=> select * from default.test_dm " --read_tso "90000000
 ┌─col_1─┬─_tidb_rowid─┐
 │    13 │           1 │
 │ 10086 │           3 │