How to get last N connected edges - orientdb

Question

I'm writing a large scale chat application and here is my db schema:
CREATE CLASS User EXTENDS V;
CREATE PROPERTY User.name STRING;
CREATE CLASS Message EXTENDS V;
CREATE PROPERTY Message.text STRING;
CREATE PROPERTY Message.createdAt DATETIME;
CREATE INDEX Message.createdAt ON Message(createdAt) NOTUNIQUE;
CREATE CLASS Send EXTENDS E;
i'm using lightweight edges and i have 200,000 edges connected to #12:0 like this:
CREATE VERTEX User SET name = 'john';
/* #12:0 */
CREATE VERTEX Message SET content = 'Lorem ipsum dolor sit amet', createdAt = SYSDATE();
/* #20:0 */
CREATE EDGE Send FROM #12:0 TO #20:0
i want to get last 5 messages that connected to the #12:0. i tried these queries:
Query 1:
SELECT FROM (
SELECT EXPAND(OUT('Send')) FROM #12:0
) ORDER BY createdAt DESC LIMIT 5
it took ~2s
"explain" result:
{
"result": [
{
"#type": "d",
"#version": 0,
"documentReads": 200000,
"current": "#19:66661",
"recordReads": 200000,
"fetchingFromTargetElapsed": 377,
"expandElapsed": 0,
"orderByElapsed": 5,
"evaluated": 200000,
"elapsed": 2416.7283,
"resultType": "collection",
"resultSize": 5,
"#fieldTypes": "documentReads=l,current=x,recordReads=l,fetchingFromTargetElapsed=l,expandElapsed=l,orderByElapsed=l,evaluated=l,elapsed=f"
}
],
"notification": "Query executed in 2.427 sec. Returned 1 record(s)"
}
Query 2:
SELECT OUT('Send')[199994-199999] FROM #12:0
it took ~6s
"explain" result:
{
"result": [
{
"#type": "d",
"#version": 0,
"documentReads": 1,
"current": "#12:0",
"recordReads": 1,
"optimizationElapsed": 0,
"fetchingFromTargetElapsed": 8749,
"evaluated": 1,
"elapsed": 8749.445,
"resultType": "collection",
"resultSize": 1,
"#fieldTypes": "documentReads=l,current=x,recordReads=l,optimizationElapsed=l,fetchingFromTargetElapsed=l,evaluated=l,elapsed=f"
}
],
"notification": "Query executed in 8.759 sec. Returned 1 record(s)"
}
is there any faster way to do this?
please don't refer to the chat use case...
i'm using orientdb 2.2.7

Answer 1

Finally! i find a fast way to do this.
I've change my db schema to:
CREATE CLASS User EXTENDS V;
CREATE PROPERTY User.name STRING;
CREATE CLASS Message;
CREATE PROPERTY Message.text STRING;
CREATE PROPERTY Message.writer LINK User;
CREATE PROPERTY Message.createdAt DATETIME;
CREATE INDEX Message.writer ON Message(writer) NOTUNIQUE_HASH_INDEX;
CREATE INDEX Message.createdAt ON Message(createdAt) NOTUNIQUE;
I'm using Message.writer to connect to the User instead of using edge.
Query:
SELECT FROM Message
WHERE createdAt < sysdate() AND writer = #12:0
ORDER BY createdAt DESC
SKIP 10 LIMIT 5
this takes ~30ms on 1.5 million records!
IMPORTANT: Notice the createdAt < sysdate() in WHERE clause,
you have to write a dummy condition on the ORDER BY field, this makes ORDER BY to use createdAt index (~700ms faster)
"explain" result (with createdAt < sysdate()):
{
"result": [
{
"#type": "d",
"#version": 0,
"documentReads": 252,
"fullySortedByIndex": true,
"documentAnalyzedCompatibleClass": 252,
"recordReads": 252,
"fetchingFromTargetElapsed": 6,
"indexIsUsedInOrderBy": true,
"compositeIndexUsed": 1,
"current": "#49:1493348",
"involvedIndexes": [
"Message.createdAt"
],
"limit": 5,
"evaluated": 252,
"elapsed": 6.447579,
"resultType": "collection",
"resultSize": 5,
"#fieldTypes": "documentReads=l,documentAnalyzedCompatibleClass=l,recordReads=l,fetchingFromTargetElapsed=l,compositeIndexUsed=l,current=x,involvedIndexes=e,evaluated=l,user=x,elapsed=f"
}
],
"notification": "Query executed in 0.032 sec. Returned 1 record(s)"
}
"explain" result (without createdAt < sysdate()):
{
"result": [
{
"#type": "d",
"#version": 0,
"documentReads": 48512,
"fullySortedByIndex": false,
"documentAnalyzedCompatibleClass": 48512,
"recordReads": 48512,
"fetchingFromTargetElapsed": 801,
"indexIsUsedInOrderBy": false,
"compositeIndexUsed": 1,
"current": "#49:1499971",
"involvedIndexes": [
"Message.writer"
],
"limit": 5,
"orderByElapsed": 49,
"evaluated": 48512,
"elapsed": 853.48004,
"resultType": "collection",
"resultSize": 5,
"#fieldTypes": "documentReads=l,documentAnalyzedCompatibleClass=l,recordReads=l,fetchingFromTargetElapsed=l,compositeIndexUsed=l,current=x,involvedIndexes=e,orderByElapsed=l,evaluated=l,user=x,elapsed=f"
}
],
"notification": "Query executed in 0.864 sec. Returned 1 record(s)"
}