When does MySQL begin to start sending data to a client?

I am working on MySQL 5.7 with the default configuration of InnoDB storage engine. I have 2 questions each for a different scenario and need to know the internal working on how MySQL sends data to the client.

Scenario 1:

If there is a select query on a very large data (Say 1 GB), does MySQL pull the entire data from the disk (from .idb files) to the InnoDB Buffer Pool or does it send data to the client in batches without exhausting the server’s memory?

Scenario 2:

A simple inner join of 2 tables without order by or group by clause (i.e the ordering of data doesn’t matter). In such case, does MySQL send the data as and when the join data is accumulated (i.e in batches) or does it construct the entire join result in the Buffer pool and sends the data after? Is the entire data loaded in-memory?

The my.cnf configuration of my local machine is as follows.

[mysqld] performance_schema=OFF innodb_buffer_pool_load_at_startup=OFF innodb_buffer_pool_dump_at_shutdown=OFF innodb_buffer_pool_size=4294967296  secure-file-priv = "" 

Note: I have disabled the buffer pool load on shutdown and startup so as to simulate the condition where none of data is cached when the server is started.

ssh.service failed to start “start-limit-hit” after dist-upgrade and restart

I was updating my Ubuntu 16.04 server with apt-get update and apt-get upgrade and then I restarted the server with sudo reboot. Since then, I can’t login via putty. I connected via console that my hosting provider gives and running the command sudo service ssh status i got the following :

enter image description here

Any advise how can I handle this?

Windows feature that stores specific data about applications run to help them start faster? [migrated]

do you know of a Windows feature that stores specific data about applications run to help them start faster? Asking because a forensics challenge I’m attempting to do had that as a hint to find the most recently run executable. Can I get any help?

macOS Mojave clean install installer doesn’t start

I wish to perform a clean install of macOS Mojave on my Mid 2013 MacBook Air. I am currently running macOS High Sierra 10.13.6.

I’ve done all the steps, from downloading the installer from the Mac App Store, to creating a bootable USB using the follow command:

sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled -- /Applications/Install\ macOS\ Mojave.app 

Then I rebooted my Mac with the USB flash drive plugged in, holding down the Option key, and got to the select boot media screen.

When I select the USB flash drive to start the installer, I got a black screen with Apple logo and a progress bar. That went well and fill the 100% bar, but then nothing happens.

I’ve already waited for like 4 hours with nothing happening.

Can anybody help me with what’s going wrong?

I just want to format my Mac to have a fresh start without any junk files.

Kafka consumer : Resetting offset for partition xxxx1-0 to offset 25143.Every time I start it

Toptic-A:

o.a.k.c.c.i.ConsumerCoordinator - [Consumer clientId=consumer-1, groupId=group-5] Revoking previously assigned partitions [] o.a.k.c.c.i.AbstractCoordinator - [Consumer clientId=consumer-1, groupId=group-5] (Re-)joining group o.a.k.c.c.i.AbstractCoordinator - [Consumer clientId=consumer-1, groupId=group-5] Successfully joined group with generation 1 o.a.k.c.c.i.ConsumerCoordinator - [Consumer clientId=consumer-1, groupId=group-5] Setting newly assigned partitions [A1-0] o.a.k.c.consumer.internals.Fetcher - [Consumer clientId=consumer-1, groupId=group-5] Resetting offset for partition A1-0 to offset 25143. 

last message:

o.a.k.c.consumer.internals.Fetcher - [Consumer clientId=consumer-1, groupId=group-5] Resetting offset for partition A1-0 to offset 25143. 

This causes me to reset the offset every time I start,Let’s say I run to number 25200,then I turn off that,the offset is reset to 25143 the next time I start, but I want to continue with the last offset.

This is another toptic,and this is the normal result I want:
Toptic-wallet:

org.apache.kafka.clients.Metadata - Cluster ID: iQU30Fo1TViA2rkH9cxVYQ o.a.k.c.c.i.AbstractCoordinator - [Consumer clientId=consumer-3, groupId=wallet-1] Discovered group coordinator localhost:9092 (id: 2147483646 rack: null) o.a.k.c.c.i.ConsumerCoordinator - [Consumer clientId=consumer-3, groupId=wallet-1] Revoking previously assigned partitions [] o.a.k.c.c.i.AbstractCoordinator - [Consumer clientId=consumer-3, groupId=wallet-1] (Re-)joining group o.a.k.c.c.i.AbstractCoordinator - [Consumer clientId=consumer-3, groupId=wallet-1] Successfully joined group with generation 13 o.a.k.c.c.i.ConsumerCoordinator - [Consumer clientId=consumer-3, groupId=wallet-1] Setting newly assigned partitions [blockaddresscomplete3-0] 

How should I set Toptic-A.

Why does iTunes stick on “Waiting for sync to start” when using WiFi sync?

Sometimes I get “Looking for iPhone” and then a silent failure. Sometimes it finds the iPhone and sticks on “Waiting for sync to start” long enough (more than 10 minutes) that I forget and/or try to quit iTunes. When I try to quit I usually have to force-quit if I actually want to get out of iTunes. I never get any error messages, just silent failures or iTunes frozen/not responding.

Sometimes a force-quit and relaunch gets things going, sometimes not. Just now after a force-quit/restart iTunes silently gave up after looking for the iPhone about 4 times and on the 5th try finally worked fine.

iPhone is on the same wifi network as the Mac running iTunes.

SSH failed to start – Missing privilege separation directory: /var/run/sshd

I have a VPS running Ubuntu 16.04.5 that’s been going for a number of years now with little issue. Today, however, I found I was unable to access the server using SSH, receiving ‘connection refused’ errors. I accessed the server using my VPS host’s serial console service, and traced the issue down to openssh server failing to start. Here’s an output of service status, service start, and sshd -t following a fresh reboot:

root@167:/# service ssh status ● ssh.service - OpenBSD Secure Shell server    Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled)    Active: failed (Result: start-limit-hit) since Fri 2019-01-18 04:56:42 EST; 24min ago   Process: 983 ExecStartPre=/usr/sbin/sshd -t (code=exited, status=255)  Jan 18 04:56:42 167 systemd[1]: Failed to start OpenBSD Secure Shell server. Jan 18 04:56:42 167 systemd[1]: ssh.service: Unit entered failed state. Jan 18 04:56:42 167 systemd[1]: ssh.service: Failed with result 'exit-code'. Jan 18 04:56:42 167 systemd[1]: ssh.service: Service hold-off time over, scheduling restart. Jan 18 04:56:42 167 systemd[1]: Stopped OpenBSD Secure Shell server. Jan 18 04:56:42 167 systemd[1]: ssh.service: Start request repeated too quickly. Jan 18 04:56:42 167 systemd[1]: Failed to start OpenBSD Secure Shell server. Jan 18 04:56:42 167 systemd[1]: ssh.service: Unit entered failed state. Jan 18 04:56:42 167 systemd[1]: ssh.service: Failed with result 'start-limit-hit'. root@167:/# service ssh start Job for ssh.service failed because the control process exited with error code. See "systemctl status ssh.service" and "journalctl -xe" for details. root@167:/# sshd -t Missing privilege separation directory: /var/run/sshd 

I’ve attempted some research into this, but nothing that’s come up seems to have an actual solution – Just endless cycles of ‘I have this problem’ with no answers, answers that are outdated, or just generally unhelpful information.

Does anybody have any ideas on what to do next to troubleshoot/resolve this issue? SSH was last working about 12 hours ago when I logged in to run updates and rebooted the server.

Service lifecycle with non blocking start and stop

So the basic scenario is I have a class that starts/stops service objects with the methods start(String serviceid)/stop(String serviceid). It is designed to then forward various execution tasks to the appropriate service.

What I am trying to achieve is for the start/stop methods to be non-blocking. Hence if you start you may stop immediately afterwards.

However your services may not have been initialised yet if you try to stop them after you request a start – so you want to cancel the startup process reliably. I also have methods to start/stop all defined services. The startup of a service is also bound to a timeout parameter so if it fails to start in that time it is again stopped.

Currently I have an implementation mostly based around the Executor classes. When starting a new initialisation task is created in a single thread executor. Within this is another timeout single thread executor. The initialisation task is submitted there. So in essence:

Runnable failedTask; Runnable initialisedTask; Callable<Exception> serviceInitialisationTask; ExecutorService initialisationExecutor = Executors.newSingleThreadExecutor(); ExecutorService timeoutExecutor = Executors.newSingleThreadExecutor(); timeoutExecutor.execute(() -> {     Future<Exception> future = initialisationExecutor.submit(serviceInitialisationTask);     Exception futureException;     try {         futureException = future.get(timeout, timeunit);     } catch (Exception e) {         futureException = e;     } finally {         initialisationExecutor.shutdownNow();     }     // Call back to the class that started the service initialisation     // This tells it whether or not the task failed and take action     if (futureException != null) {          failedTask.run();     } else {         initialisedTask.run();     }      timeoutExecutor.shutdownNow(); }); 

The initialisation task essentially creates a thread pool for the Service to execute tasks on. Failure attempts to use the same stop method as called externally. A concurrent map stores references to the servers by id. Sometimes the thread pools for the Service remain – presumably because the new service was created before the reference to the old one was used.

If that is clear does anyone know of anything that uses this sort of pattern? I have not been able to find anything that matches this but I cannot be the first person to attempt a system like this. I’m not tied to any particular way of doing this – the only thing I would like is to not have to block starting and stopping to the caller.