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Properly handle the caching of Cypher queries within metaqueries

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Reviewers: mtomic, teon.banek

Reviewed By: teon.banek

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1800
This commit is contained in:
Lovro Lugovic 2019-01-16 11:43:04 +01:00
parent 2133895db1
commit 12c8b3f75f
1 changed files with 41 additions and 11 deletions
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52
src/query/interpreter.cpp
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@ -590,7 +590,6 @@ Interpreter::Results Interpreter::operator()(
#endif
AstStorage ast_storage;
Context execution_context(db_accessor);
Parameters parameters;
std::map<std::string, TypedValue> summary;
@ -645,11 +644,36 @@ Interpreter::Results Interpreter::operator()(
<< "Expected stripped query to start with '" << kExplainQueryStart
<< "'";
auto cypher_query_hash =
fnv(stripped_query.query().substr(kExplainQueryStart.size()));
std::shared_ptr<CachedPlan> cypher_query_plan =
CypherQueryToPlan(cypher_query_hash, explain_query->cypher_query_,
std::move(ast_storage), parameters, &db_accessor);
// We want to cache the Cypher query that appears within this "metaquery".
// However, we can't just use the hash of that Cypher query string (as the
// cache key) but then continue to use the AST that was constructed with the
// full string. The parameters within the AST are looked up using their
// token positions, which depend on the query string as they're computed at
// the time the query string is parsed. So, for example, if one first runs
// EXPLAIN (or PROFILE) on a Cypher query and *then* runs the same Cypher
// query standalone, the second execution will crash because the cached AST
// (constructed using the first query string but cached using the substring
// (equivalent to the second query string)) will use the old token
// positions. For that reason, we fully strip and parse the substring as
// well.
//
// Note that the stripped subquery string's hash will be equivalent to the
// hash of the stripped query as if it was run standalone. This guarantees
// that we will reuse any cached plans from before, rather than create a new
// one every time. This is important because the planner takes the values of
// the query parameters into account when planning and might produce a
// totally different plan if we were to create a new one right now. Doing so
// would result in discrepancies between the explained (or profiled) plan
// and the one that's executed when the query is ran standalone.
auto queries =
StripAndParseQuery(query_string.substr(kExplainQueryStart.size()),
&parameters, &ast_storage, &db_accessor, params);
StrippedQuery &stripped_query = queries.first;
ParsedQuery &parsed_query = queries.second;
std::shared_ptr<CachedPlan> cypher_query_plan = CypherQueryToPlan(
stripped_query.hash(), dynamic_cast<CypherQuery *>(parsed_query.query),
std::move(ast_storage), parameters, &db_accessor);
std::stringstream printed_plan;
PrettyPrintPlan(db_accessor, &cypher_query_plan->plan(), &printed_plan);
@ -694,11 +718,17 @@ Interpreter::Results Interpreter::operator()(
throw QueryException("TSC support is missing for PROFILE");
}
auto cypher_query_hash =
fnv(stripped_query.query().substr(kProfileQueryStart.size()));
auto cypher_query_plan =
CypherQueryToPlan(cypher_query_hash, profile_query->cypher_query_,
std::move(ast_storage), parameters, &db_accessor);
// See the comment regarding the caching of Cypher queries within
// "metaqueries" for explain queries
auto queries =
StripAndParseQuery(query_string.substr(kProfileQueryStart.size()),
&parameters, &ast_storage, &db_accessor, params);
StrippedQuery &stripped_query = queries.first;
ParsedQuery &parsed_query = queries.second;
auto cypher_query_plan = CypherQueryToPlan(
stripped_query.hash(), dynamic_cast<CypherQuery *>(parsed_query.query),
std::move(ast_storage), parameters, &db_accessor);
// Copy the symbol table and add our own symbols (used by the `OutputTable`
// operator below)