.pQd – Page 4 – .pQd's log

ClickHouse – dictionary with string keys

2021-09-032022-02-24 by .pQd

i wanted to create a clickhouse dictionary that used String as a key, not an int. docs mention here: “A composite key can consist of a single element. This makes it possible to use a string as the key, for instance”. I’ve been trying this and failed few times. creation worked but i could not ... Read More

“initramfs unpacking failed: write error” due to stupid typo in virsh-install

2021-08-262021-08-27 by .pQd

i’ve been trying to set up a new vm using: trying and trying, and each time i got the same boot failure: root cause? allocating 128MB instead of intended 128GB of RAM for the VM. hopefully this post helps some poor soul who runs into a similar issue.

clickhouse – getting n most significant digits of a number

2021-08-212021-08-22 by .pQd

i’m testing some wild idea of finding matches in quite a large dataset. part of the problem is that scaling of input is unknown, 123 might be correct match for 1.23 or for 12.3. here’s an expression that returns me n=4 most significant digits of each float from the input array:

suddenly in-kernel communication between lxc containers gets erratic

2021-08-172021-08-20 by .pQd

we’re using LXC containers to host multiple workloads on the same physical servers. e.g. few instances of database servers running side-by-side. once in a while we end up with strange situation where tcp connections between containers running on the same physical server get torn down abruptly. in our case – this manifested e.g. by those ... Read More

apache2 – redirect from http to https with some source-ip-based exceptions

2021-08-02 by .pQd

i was migrating a server from http to https. while header-based redirect worked for most of the clients, for some – i had to allow for a transition period where some configuration / code had to be adjusted. here’s the config that responds with 302 redir to most of the http requests, but for those ... Read More

switching source of SVN replica

2021-07-152021-07-15 by .pQd

i have svn replica that follows in near-real-time a master server using below run every few seconds: i had to change url of the source server; to reconfigure the the replica i’ve done:

changing source url of the svn repository replica

2021-04-202021-04-20 by .pQd

i have bunch of svn read-only replicas. they were created using: replication [ fetching of earlier not downloaded revisions ] is done via: to check from which url my replica repo fetches updates: to change it – run: that’s it – next execution of svnsync will fetch the data from the new origin url based ... Read More

fiddler returning “HTTP/1.1 502 Fiddler – Connection Failed” for HTTPs requests replied / made with it?

2021-04-152021-04-15 by .pQd

i’ve been using fiddler tool for ages. recently i’ve noticed most of my attempts of sending new requests fail with: solution? tools > options > [x] capture HTTPS CONNECTs > [x] Decrypt HTTPS traffic > protocols: enter there tls1.2 once it’s set you can un-tick [x] capture.

“Verify your Kindle document” for pdfs self-mailed to my kindle

2021-04-052021-04-05 by .pQd

whenever i travel i like to use kindle for reading some articles that i’ve earlier collected. for collecting i use a simple PHP script with rich text editor that allows me to copy & paste content and then mail it to my kindle address. recently i’ve started getting requests from Amazon to approve each document ... Read More

xiaomi robot vaccuum disassembly

2021-03-062021-03-06 by .pQd

i have 1st gen xiaomi mi robot vacuum cleaner. it’s been serving very well for the past 3 years. this video was very helpful with disassembly when i had to replace the main sucking motor fan: https://www.youtube.com/watch?v=wdDSBgJ1kRM i had to replace a fan and bought https://www.aliexpress.com/item/4000804127893.html instead of https://www.aliexpress.com/item/4000259186760.html ; not an exact fit but ... Read More

clickhouse

2021-02-212023-01-05 by .pQd

clickhouse is a column oriented OLAP database. i’ve started using it about half a year ago. i’m impressed. earlier i’ve read about it on percona’s blog but did not fully grasp how performant it was. i’ve tried it when i wrestling with MariaDB’s query planner on table with ~100M rows got me tired and each ... Read More

supermicro server getting stuck on “loading initial ramdisk”

2021-01-302021-02-19 by .pQd

i had a quite puzzling moment today when a server refused to boot up after routine maintenance. order of events: datacenter technician has taken server down and added Mellanox 25Gbit network card server booted up cleanly with Debian Buster and aged kernel 4.19.0-6 i’ve rebooted the server again and changed cpu performance settings in bios ... Read More

supermicro IPMI – mounting iso image via samba

2021-01-30 by .pQd

reminder for my self in case i need to do it again, relevant for X11DDW-NT and likely – other their platforms: log-in to the IPMI web interface, go to virtual media > CD-ROM image, provide: share host – ip or hostname of samba server. for instance: 10.1.2.3 paht to image – backlash share name backslash ... Read More

letting dbeaver talk with manticoresearch

2021-01-162021-01-16 by .pQd

here’s what i did to get dbeaver 7.3.2 + oracle’s JDBC mysql-connector-java-8.0.17.jar work with manticoresearch 3.5.4: /etc/manticoresearch/manticore.conf, under searchd: in dbeaver – new connection using oracle’s JDBC driver as above, under data editor – set ResultFetchSize to 0 to prevent errors like this: when i initially tried to get it working with JDBC driver from ... Read More

live-resizing KVM VM disk backed by qcow2 file

2021-01-102021-01-10 by .pQd

let’s say you have KVM VM with Linux and you’d like to resize its qcow2-backed disk without shutting down VM.

black hole, somewhere in the internet, swallowing UDP packets

2020-12-052022-01-26 by .pQd

UDP packets sent from specific source port, with public source IP address do not reach specific destination port of the public destination IP address. changing any of the parameters [ usually source port ] – fixes the issue. i’ve observed this phenomenon multiple times for long-running OpenVPN and Wireguard VPNs encapsulating encrypted traffic in UDP ... Read More

spooky HTTP requests arriving from the dark corners of the internet

2020-11-012020-11-01 by .pQd

i’ve spent most of the last week investigating spooky HTTP request that we’ve found in access logs of few production servers. very likely that traffic was replayed by mail content scanners used by messagelabs and mimecast.

UPC WiFree on Mikrotik and OpenWRT

2020-10-172023-03-22 by .pQd

UPC turns your cable modem into WiFi hot-spot available for others. outrageous! and i’ve been using it for quite a while – it generally works. below – how to connect OpenWRT or Mikrotik to such connection.

using dedicated server from hetzner

2020-09-252023-07-03 by .pQd

4 months ago i’ve started renting a dedicated server at https://www.hetzner.com/ and – so far – i’m quite happy with the service. i’ve picked cheapest suitable hardware from their auctions, after a month of trouble-free usage i’ve switched to quarterly billing. then server has crashed few times with “shutting down cpus with nmi” kernel messages. ... Read More

resizing btrfs on luks on mdadm raid10

2020-09-18 by .pQd

one of my KVM VMs keeps data on BTRFS on top of encrypted LUKS drive. that drive is a block device passed from virtualization server to VM… a block device which is mdadm software RAID10. below – steps taken to resize it.