mysql - Efficiency of query using NOT IN()? -


i have query runs on server:

delete pairing id not in (select f.id info f)

it takes 2 different tables, pairing , info , says delete entries pairing whenever id of pairing not in info.

i've run issue on server beginning take long execute, , believe has efficiency (or lack of constraints in select statement).

however, took @ mysql slow_log , number of compared entries lower should be. understanding, should o(mn) time m number of entries in pairing , n number of entries in info. number of entries in pairing 26,868 , in info 34,976.

this should add 939,735,168 comparisons. slow_log saying there 543,916,401: half amount.

i wondering if please explain me how efficiency of specific query works. realize fact it's performing quicker think should blessing in case, still need understand optimization comes can further improve upon it.

i haven't used slow query log (at all) isn't possible difference can chalked simple... can't think of word. basically, 939,735,168 theoretical worst case scenario query literally checks every single row except 1 needs first. realistically, distribution (and no use of indexing), check of row in pairing on average compare half rows in info.

it looks real world performance 15% off (worse) expected "average comparisons".

edit: actually, "worse expected" should expected when have rows in pairing not in info, skew number of comparisons.

...which still not great. if have id indexed in both tables, should work lot faster.

delete pairing  pairing left join info on pairing.id = info.id  info.id null ;

this should take advantage of index on id make comparisons needed o(nlogm).


Comments

Post a Comment

Popular posts from this blog

python Tkinter Capturing keyboard events save as one single string -

is possible store keyboard events 1 string? code below stores 1 char , prints it. card reader or bar code reader, contains collection of character/ string not 1 character @ time. goal save char pressed text variable. from tkinter import * root = tk() def key(event): text= event.char text+= event.char print ("pressed", text) def callback(event): frame.focus_set() print ("clicked at", event.x, event.y) frame = frame(root, width=100, height=100) frame.bind("<key>", key) frame.bind("<button-1>", callback) frame.pack() root.mainloop() currently, creating text variable , everytime key() function gets called, , text stores last character typed. you can define text module level variable , , use module level text inside key function - text = '' def key(event): global text text+= event.char print("pressed", text)
Read more

android - InAppBilling registering BroadcastReceiver in AndroidManifest -

i'm implementing inapp billing in android app. works well, however, i'm trying decouple broadcast receiver activity manifest. suggestion in android's trivialdrive sample: // important: dynamically register broadcast messages updated purchases. // register receiver here instead of <receiver> in manifest // because call getpurchases() @ startup, therefore can ignore // broadcasts sent while app isn't running. // note: registering listener in activity bad idea, done here // because sample. regardless, receiver must registered after // iabhelper setup, before first call getpurchases(). currently there's class extends broadcastreceiver : public class iabbroadcastreceiver extends broadcastreceiver { /** * intent action receiver should filter for. */ public static final string action = "com.android.vending.billing.purchases_updated"; private final iabbroadcastlistener mlistener; public iabbroadcastreceiver(iabbroadcastlistener listener) { m
Read more

javascript - Z-index in d3.js -

i have map , when hover effect on region of map below yellow line , circle, last ones disappear. how can solve problem? http://jsfiddle.net/ot21n9qx/ var arc = g.append("path") .style("fill", "none") .style("stroke", "yellow") .style("stroke-width", 2) .attr("d", "m" + pathorigin[0] + "," + pathorigin[1] + " q" + svgpoint[0] + "," + pathorigin[1] + " " + svgpoint[0] + "," + svgpoint[1]); var circlesize = d3.scale.linear() .domain([0, 0.5, 1]) .range([4, 10, 4]); svg not have z order draws objects in order created. need create path , circle after create highlight regions. here forked fiddle: http://jsfiddle.net/o00fzgaf/1/
Read more