Add option to use a temporary view instead of a table to reduce WAL churn during SqlMerge

2 files changed, 37 insertions, 13 deletions

diff --git a/project2/sqlMergeTask.cpp b/project2/sqlMergeTask.cpp
index 495a689..d59d356 100644
--- a/project2/sqlMergeTask.cpp
+++ b/project2/sqlMergeTask.cpp
@@ -4,6 +4,7 @@
 #include <misc.h>
 #include <stdio.h>
 #include <stdexcept>
+#include <boost/algorithm/string/join.hpp>
 
 bool _SqlMergeTask::defaultUseTempTable = true;
 static void attach(Iterate i, ModifyCommand * insert);
@@ -15,6 +16,7 @@ _SqlMergeTask::_SqlMergeTask(const xmlpp::Element * p) :
 	updateWhere(p->get_attribute_value("updatewhere")),
 	patchOrder(p->get_attribute_value("patchorder")),
 	earlyKeys(p->get_attribute_value("earlykeys") == "yes"),
+	useView(p->get_attribute_value("useview") == "yes"),
 	tempTableCreated(false),
 	insCmd(NULL),
 	destdb(NULL),
@@ -25,12 +27,18 @@ _SqlMergeTask::_SqlMergeTask(const xmlpp::Element * p) :
 	Loaders loaders;
 	_Iterate::AddLoaders(loaders, sources);
 	_LoaderBase::collectAll(loaders, "project2", p, true, true);
+	if (!sources.empty() && useView) {
+		throw std::runtime_error("useview not supported with iterate fillers");
+	}
 
 	BOOST_FOREACH(xmlpp::Node * psi, p->find("columns/column")) {
 		xmlpp::Element * e = static_cast<xmlpp::Element *>(psi);
 		TargetColumnPtr tcp(new TargetColumn(e->get_child_text()->get_content()));
 		tcp->maptable = e->get_attribute_value("maptable");
 		if (!tcp->maptable.empty()) {
+			if (useView) {
+				throw std::runtime_error("useview not supported with mapped columns");
+			}
 			tcp->mapcolumn = e->get_attribute_value("mapcolumn");
 		}
 		cols.insert(tcp);
@@ -95,16 +103,24 @@ _SqlMergeTask::execute() const
 void
 _SqlMergeTask::createTempTable() const
 {
-	ModifyCommand(*destdb, stringf(
-				"CREATE TEMPORARY TABLE %s AS SELECT * FROM %s WHERE 0=1",
-				dtablet.c_str(),
-				dtable.c_str())).execute();
-	BOOST_FOREACH(Columns::value_type c, cols) {
-		if (!c->maptable.empty()) {
-			ModifyCommand(*destdb, stringf(
-						"ALTER TABLE %s ADD COLUMN %s VARCHAR(1000)",
-						dtablet.c_str(),
-						c->mapcolumn.c_str())).execute();
+	if (useView) {
+		ModifyCommand(*destdb, stringf(
+					"CREATE VIEW %s AS %s",
+					dtablet.c_str(),
+					boost::algorithm::join(sqls, " UNION ").c_str())).execute();
+	}
+	else {
+		ModifyCommand(*destdb, stringf(
+					"CREATE TEMPORARY TABLE %s AS SELECT * FROM %s WHERE 0=1",
+					dtablet.c_str(),
+					dtable.c_str())).execute();
+		BOOST_FOREACH(Columns::value_type c, cols) {
+			if (!c->maptable.empty()) {
+				ModifyCommand(*destdb, stringf(
+							"ALTER TABLE %s ADD COLUMN %s VARCHAR(1000)",
+							dtablet.c_str(),
+							c->mapcolumn.c_str())).execute();
+			}
 		}
 	}
 	tempTableCreated = true;
@@ -113,12 +129,18 @@ void
 _SqlMergeTask::dropTempTable() const
 {
 	if (tempTableCreated) {
-		ModifyCommand(*destdb, "DROP TABLE " + dtablet).execute();
+		if (useView) {
+			ModifyCommand(*destdb, "DROP VIEW " + dtablet).execute();
+		}
+		else {
+			ModifyCommand(*destdb, "DROP TABLE " + dtablet).execute();
+		}
 	}
 }
 void
 _SqlMergeTask::createTempKey() const
 {
+	if (useView) return;
 	/* Primary key */
 	Buffer idx;
 	idx.appendf("ALTER TABLE %s ADD CONSTRAINT pk_%s PRIMARY KEY(",
@@ -218,6 +240,7 @@ static void attach(Iterate i, ModifyCommand * insert)
 void
 _SqlMergeTask::copyToTempTable() const
 {
+	if (useView) return;
 	BOOST_FOREACH(const Iterates::value_type & i, sources) {
 		i.second->execute();
 	}
diff --git a/project2/sqlMergeTask.h b/project2/sqlMergeTask.h
index 16dcdc7..ce10f70 100644
--- a/project2/sqlMergeTask.h
+++ b/project2/sqlMergeTask.h
@@ -44,9 +44,10 @@ class _SqlMergeTask : public _Task {
         Columns	           		cols;
         Keys                    keys;
         Keys                    indexes;
-        const Variable		updateWhere;
+        const Variable			updateWhere;
         const std::string       patchOrder;
-        bool                    earlyKeys;
+        const bool				earlyKeys;
+		const bool				useView;
 
     private:
         virtual void            copyToTempTable() const;