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/// <reference path="lodash.d.ts" />
export class HelpService {
getNodeTypeDescription(nodeType: string) {
return NODE_DESCRIPTIONS[nodeType.toUpperCase()];
}
}
export var NODE_DESCRIPTIONS = {
'LIMIT':'returns a specified number of rows from a record set.',
'SORT': 'sorts a record set based on the specified sort key.',
'NESTED LOOP': `merges two record sets by looping through every record in the first set and
trying to find a match in the second set. All matching records are returned.`,
'MERGE JOIN': `merges two record sets by first sorting them on a <strong>join key</strong>.`,
'HASH': `generates a hash table from the records in the input recordset. Hash is used by
<strong>Hash Join</strong>.`,
'HASH JOIN': `joins to record sets by hashing one of them (using a <strong>Hash Scan</scan>).`,
'AGGREGATE': `groups records together based on a GROUP BY or aggregate function (like <code>sum()</code>).`,
'HASHAGGREGATE': `groups records together based on a GROUP BY or aggregate function (like sum()). Hash Aggregate uses
a hash to first organize the records by a key.`,
'SEQ SCAN': `finds relevant records by sequentially scanning the input record set. When reading from a table,
Seq Scans (unlike Index Scans) perform a single read operation (only the table is read).`,
'INDEX SCAN': `finds relevant records based on an <strong>Index</strong>. Index Scans perform 2 read operations: one to
read the index and another to read the actual value from the table.`,
'INDEX ONLY SCAN': `finds relevant records based on an <strong>Index</strong>. Index Only Scans perform a single read operation
from the index and do not read from the corresponding table.`,
'BITMAP HEAP SCAN': 'searches through the pages returned by the <strong>Bitmap Index Scan</strong> for relevant rows.',
'BITMAP INDEX SCAN': `uses a <strong>Bitmap Index</strong> (index which uses 1 bit per page) to find all relevant pages.
Results of this node are fed to the <strong>Bitmap Heap Scan</strong>.`,
'CTE SCAN': `performs a sequential scan of <strong>Common Table Expression (CTE) query</strong> results. Note that
results of a CTE are materialized (calculated and temporarily stored).`
};
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