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Database Development

Postgres tracking count of recent items in count table or by selecting count of recent records from history table

Which would generally be more efficient, or does it not matter? Option 1 is incrementing a count in a table that stores counts by the unique id, and resetting the count to zero when enough time has passed for that unique id. Option 2 is not storing a count and fetching the count of records […]

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Ask Chemistry

electrolysis with baking soda solution

I setup an electrolysis experiment to show my kids, and wanted to explain to them what is happening. My setup has a penny as the cathode and graphite for the anode. The solution is water with baking soda mixed in. I see bubbles at each of the electrodes which I assume are Hydrogen and Oxygen […]

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Ask Chemistry

How does the solubility of hydrated ions differ from unhydrated ions?

So the hydrated compound I am thinking about specifically is pentahydrate copper sulphate. I know when you put ionic compounds in water, the ions because hydrated by the water molecules. However, what happens when you are already putting a hydrated ion into the water? I think the solubility is supposed to be lower, but I […]

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Bitcoin Cryptocurrency Mastering Development

What do “support” and “resistance” mean?

I’m still very much a newbie to all this and would like to get some help.

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Linux Mastering Development

Error: transaction check vs depsolve… php dependencies

I’m trying to run sudo dnf system-upgrade download –refresh –releasever=30 –allowerasing (from fedora 25) and hitting the following errors. Running transaction check Error: transaction check vs depsolve: (php-composer(symfony/expression-language) >= 2.8 with php-composer(symfony/expression-language) < 5) is needed by php-phpmyadmin-motranslator-4.0-4.fc30.noarch (gcc >= 9 with gcc < 10) is needed by annobin-8.71-4.fc30.x86_64 (php-composer(symfony/translation) >= 2.7.1 with php-composer(symfony/translation) < […]

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Linux Mastering Development

Make wget save a page files in a single specific directory

When I save webpage page via Firefox I get a directory structure like this: . ├── Some Page/ └── Some Page.html So we have got a single .html file and a folder which contains images, javascript, css, etc. Can I obtain the same result (html + single big folder) with wget (or any other command-line […]

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Linux Mastering Development

Upgrading Fedora 25 to 32 “rpmlib(PayloadIsZstd) <= 5.4.18-1 is needed by …" errors

After running sudo dnf system-upgrade download –refresh –releasever=32 –allowerasing I get the following gigantic list of errors: rpmlib(PayloadIsZstd) <= 5.4.18-1 is needed by python3-audit-3.0-0.19.20191104git1c2f876.fc32.x86_64 rpmlib(PayloadIsZstd) <= 5.4.18-1 is needed by kexi-3.1.0-7.fc32.x86_64 rpmlib(PayloadIsZstd) <= 5.4.18-1 is needed by kexi-libs-3.1.0-7.fc32.x86_64 rpmlib(PayloadIsZstd) <= 5.4.18-1 is needed by alternatives-1.11-6.fc32.x86_64 … After reading https://serverfault.com/questions/280099/how-do-i-install-an-rpm-that-complains-about-rpmlibfiledigests-4-6-0-1 I gather this is because some […]

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Linux Mastering Development

Why does terminal output seem to be affected by stdout and stderr redirection

I am trying to get a certain piece of output from running a command in my Mac terminal. I’ve noticed that when I run my-command 2> a.txt, I am able to see it in the text file and it no longer outputs in the terminal. However, when I run my_command 1> a.txt, I don’t see […]

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Linux Mastering Development

Fail to install tcpdump package in UBI8 (Read hat Universal Base Image)

I am building a docker image based on UBI8(Read hat Universal Base Image), Dockerfile looks like FROM registry.access.redhat.com/ubi8/ubi-minimal RUN microdnf install sudo zip tar bash procps openssl iptables net-tools tcpdump && microdnf update; microdnf clean all ENTRYPOINT [ "/usr/sbin/tcpdump" ] But it failed to install tcpdump package. Downloading metadata… error: No package matches ‘tcpdump’ (process:57): […]

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Linux Mastering Development

Need some help to build my script

If I wanted to see the contents of one file data in another file how can i see that? For example I have one file named test inside which i have some path contents and another file test1 which has less path content: Inside test file: /home/ram/a.txt /home/ram/b.txt /home/shyam/c.txt /home/bhim/a.txt Inside test1 file: /home/ram/a.txt I […]