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features: run single-shot multi-query sub-queries concurrently #558

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2 changes: 1 addition & 1 deletion gradle/layers.versions.toml
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
[versions]
xtraplatform-core = '7.0.0-SNAPSHOT'
xtraplatform-core = '7.0.0-reactive-concurrent-flatmap-SNAPSHOT'
xtraplatform-native = '2.6.0-SNAPSHOT'

132 changes: 94 additions & 38 deletions ...tform-features-sql/src/main/java/de/ii/xtraplatform/features/sql/domain/SqlConnector.java
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@
import java.util.Objects;
import java.util.Optional;
import java.util.OptionalLong;
import java.util.concurrent.Semaphore;
import java.util.function.Function;
import java.util.function.IntFunction;
import java.util.stream.Collectors;
Expand All @@ -34,6 +35,12 @@ public interface SqlConnector

int getMaxConnections();

/**
* Shared budget of connection permits (sized to the connection pool) that bounds how many
* connections the concurrently running single-shot sub-queries hold at once, across all requests.
*/
Semaphore getConnectionBudget();

int getMinConnections();

int getQueueSize();
Expand Down Expand Up @@ -111,6 +118,9 @@ void register(String currentTable, SqlRowMeta metaResult) {
}
}

// Per-sub-query row buffer for the concurrent single-shot value phase (see getSourceStream).
int UNPAGED_SUBQUERY_PREFETCH = 256;

// TODO: simplify, class SqlQueryRunner, remove options, singleFeature
@Override
default Reactive.Source<SqlRow> getSourceStream(
Expand Down Expand Up @@ -218,48 +228,94 @@ default Reactive.Source<SqlRow> getSourceStream(
.build();
// a server-side cursor keeps memory bounded while streaming all rows
int fetchSize = unpaged ? (int) queryBatch.getChunkSize() : 0;
Function<Integer, Source<SqlRow>> valuePhase =
index -> {
int[] i = {0};
Source<SqlRow>[] sqlRows =
querySets
.get(index)
.getValueQueries()
.apply(sqlRowMeta, 0L, 0L)
.map(
valueQuery ->
getSqlClient()
.getSourceStream(
valueQuery,
new ImmutableSqlQueryOptions.Builder()
.from(options)
.tableSchema(
querySets
.get(index)
.getTableSchemas()
.get(i[0]))
.type(
querySets
.get(index)
.getOptions()
.getType())
.containerPriority(i[0]++)
.queryIndex(
querySets.get(index).getQueryIndex())
.fetchSize(fetchSize)
.isParallel(unpaged)
.build()))
.toArray((IntFunction<Source<SqlRow>[]>) Source[]::new);

Source<SqlRow> merged = mergeAndSort(sqlRows);

if (!unpaged) {
return merged;
}

// Bound the connections held by concurrently running sub-queries: a
// sub-query needs all its table connections at once, so acquire them
// as
// a block before its rows are read and release them when it
// terminates.
// The semaphore is shared across requests, so concurrent searches can
// never deadlock by each grabbing part of the pool.
int tables = querySets.get(index).getTableSchemas().size();
return Reactive.Source.guarded(
() -> getConnectionBudget().acquireUninterruptibly(tables),
() -> getConnectionBudget().release(tables),
merged);
};

// Single-shot multi-queries read every sub-query in one pass with no
// cross-sub-query dependency (the result sets are already materialized), so
// the sub-queries can run concurrently. Their rows are still emitted
// strictly
// in sub-query order, which the decoder requires; only the JDBC reads
// overlap.
// Concurrency is bounded so the sub-queries in flight never request more
// than
// the connection pool can serve. Single-feature reads keep the serial path.
Transformer<Integer, SqlRow> valueTransformer;
if (unpaged) {
int maxTables =
Math.max(
1,
querySets.stream()
.mapToInt(qs -> qs.getTableSchemas().size())
.max()
.orElse(1));
int maxConcurrency =
Math.max(
1,
Math.min(
querySets.size(), (getMaxConnections() - 1) / maxTables));
valueTransformer =
Transformer.flatMapConcurrent(
valuePhase, maxConcurrency, UNPAGED_SUBQUERY_PREFETCH);
} else {
valueTransformer = Transformer.flatMap(valuePhase);
}

return Source.iterable(
IntStream.range(0, querySets.size())
.boxed()
.collect(Collectors.toList()))
.via(
Transformer.flatMap(
index -> {
int[] i = {0};
Source<SqlRow>[] sqlRows =
querySets
.get(index)
.getValueQueries()
.apply(sqlRowMeta, 0L, 0L)
.map(
valueQuery ->
getSqlClient()
.getSourceStream(
valueQuery,
new ImmutableSqlQueryOptions.Builder()
.from(options)
.tableSchema(
querySets
.get(index)
.getTableSchemas()
.get(i[0]))
.type(
querySets
.get(index)
.getOptions()
.getType())
.containerPriority(i[0]++)
.queryIndex(
querySets
.get(index)
.getQueryIndex())
.fetchSize(fetchSize)
.build()))
.toArray(
(IntFunction<Source<SqlRow>[]>) Source[]::new);

return mergeAndSort(sqlRows);
}))
.via(valueTransformer)
.prepend(Source.single(sqlRowMeta));
}

Expand Down
10 changes: 10 additions & 0 deletions ...rm-features-sql/src/main/java/de/ii/xtraplatform/features/sql/domain/SqlQueryOptions.java
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Original file line number Diff line number Diff line change
Expand Up @@ -89,6 +89,16 @@ default int getFetchSize() {
return 0;
}

/**
* When enabled, the query is subscribed on a worker thread so that several such queries can
* execute concurrently (the blocking JDBC connection provider otherwise runs every query on the
* single subscribing thread). Used for the concurrent single-shot value phase.
*/
@Value.Default
default boolean isParallel() {
return false;
}

@Value.Default
default boolean isGeometryWkb() {
return false;
Expand Down
10 changes: 10 additions & 0 deletions ...form-features-sql/src/main/java/de/ii/xtraplatform/features/sql/infra/db/SqlClientRx.java
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@
import de.ii.xtraplatform.streams.domain.Reactive;
import de.ii.xtraplatform.streams.domain.Reactive.Transformer;
import io.reactivex.rxjava3.core.Flowable;
import io.reactivex.rxjava3.schedulers.Schedulers;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
Expand Down Expand Up @@ -159,6 +160,15 @@ public Reactive.Source<SqlRow> getSourceStream(String query, SqlQueryOptions opt
});
}

// The blocking connection provider runs connect+execute+read on the subscribing thread, so
// without this the whole stream is single-threaded. Subscribing on a worker thread lets several
// parallel-flagged queries (e.g. the concurrent single-shot value phase) run at once, each on
// its
// own connection.
if (options.isParallel()) {
flowable = flowable.subscribeOn(Schedulers.io());
}

return Reactive.Source.publisher(flowable);
}

Expand Down
8 changes: 8 additions & 0 deletions ...m-features-sql/src/main/java/de/ii/xtraplatform/features/sql/infra/db/SqlConnectorRx.java
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Original file line number Diff line number Diff line change
Expand Up @@ -48,6 +48,7 @@
import java.util.Map.Entry;
import java.util.Objects;
import java.util.Optional;
import java.util.concurrent.Semaphore;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.stream.Collectors;
import org.davidmoten.rxjava3.jdbc.Database;
Expand All @@ -72,6 +73,7 @@ public class SqlConnectorRx extends AbstractVolatilePolling implements SqlConnec
private final int maxConnections;
private final int minConnections;
private final int queueSize;
private final Semaphore connectionBudget;
private final Path dataDir;
private final String applicationName;
private final String providerId;
Expand Down Expand Up @@ -105,6 +107,7 @@ public SqlConnectorRx(
connectionInfo.getPool().getMinConnections() >= 0
? connectionInfo.getPool().getMinConnections()
: maxConnections;
this.connectionBudget = new Semaphore(Math.max(1, maxConnections), true);

// int capacity = maxConnections / maxQueries;
// TODO
Expand Down Expand Up @@ -138,6 +141,11 @@ public int getMaxConnections() {
return maxConnections;
}

@Override
public Semaphore getConnectionBudget() {
return connectionBudget;
}

@Override
public int getMinConnections() {
return minConnections;
Expand Down
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