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// Contains helpers for checking, based on the explain output, properties of a
// plan. For instance, there are helpers for checking whether a plan is a collection
// scan or whether the plan is covered (index only).
/**
* Given the root stage of explain's JSON representation of a query plan ('root'), returns the
* subdocument with its stage as 'stage'. Returns null if the plan does not have such a stage.
*/
function getPlanStage(root, stage) {
if (root.stage === stage) {
return root;
} else if ("inputStage" in root) {
return getPlanStage(root.inputStage, stage);
} else if ("inputStages" in root) {
for (var i = 0; i < root.inputStages.length; i++) {
var stage = getPlanStage(root.inputStages[i], stage);
if (stage !== null) {
return stage;
}
}
} else if ("shards" in root) {
for (var i = 0; i < root.shards.length; i++) {
var stage = getPlanStage(root.shards[i].winningPlan, stage);
if (stage !== null) {
return stage;
}
}
}
return null;
}
/**
* Given the root stage of explain's BSON representation of a query plan ('root'),
* returns true if the plan has a stage called 'stage'.
*/
function planHasStage(root, stage) {
return getPlanStage(root, stage) !== null;
}
/**
* A query is covered iff it does *not* have a FETCH stage or a COLLSCAN.
*
* Given the root stage of explain's BSON representation of a query plan ('root'),
* returns true if the plan is index only. Otherwise returns false.
*/
function isIndexOnly(root) {
return !planHasStage(root, "FETCH") && !planHasStage(root, "COLLSCAN");
}
/**
* Returns true if the BSON representation of a plan rooted at 'root' is using
* an index scan, and false otherwise.
*/
function isIxscan(root) {
return planHasStage(root, "IXSCAN");
}
/**
* Returns true if the BSON representation of a plan rooted at 'root' is using
* the idhack fast path, and false otherwise.
*/
function isIdhack(root) {
return planHasStage(root, "IDHACK");
}
/**
* Returns true if the BSON representation of a plan rooted at 'root' is using
* a collection scan, and false otherwise.
*/
function isCollscan(root) {
return planHasStage(root, "COLLSCAN");
}
/**
* Get the number of chunk skips for the BSON exec stats tree rooted at 'root'.
*/
function getChunkSkips(root) {
if (root.stage === "SHARDING_FILTER") {
return root.chunkSkips;
}
else if ("inputStage" in root) {
return getChunkSkips(root.inputStage);
}
else if ("inputStages" in root) {
var skips = 0;
for (var i = 0; i < root.inputStages.length; i++) {
skips += getChunkSkips(root.inputStages[0]);
}
return skips;
}
return 0;
}
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