Re: how to securely delete the storage freed when a table is dropped?

After you drop a table, aren't the associated files dropped?

On 04/13/2018 02:29 PM, Ozz Nixon wrote:
> There are free utilities that do government leave wipes. The process would be, drop the table, shrink the old table space then (if linux based), dd fill the drive, and use wipe, 5x or 8x deletion to make sure the drive does not have readable imprints on the platers.
>
> Now what Jonathan mentions - sounds like he wants to do the same to the physical table. Never dabbling into PSQL’s storage and optimization algorithms, I would first assume, a script to do a row by row update table set field1…fieldx, different data patterns, existing field value length and field max length. Run the script at least 5 to 8 times, then drop the table .. the problem will be, does PSQL use a new page as you do this, then you are just playing with yourself. Let alone, how does PSQL handle indexes - new pages, or overwrite the existing page? And is any NPI (Non-Public-Info) data in the index itself?
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> * So any PSQL core-engine guys reading?
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> O.
>
>> On Apr 13, 2018, at 3:03 PM, Ron <ronljohnsonjr(at)gmail(dot)com> wrote:
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>> On 04/13/2018 12:48 PM, Jonathan Morgan wrote:
>>> For a system with information stored in a PostgreSQL 9.5 database, in which data stored in a table that is deleted must be securely deleted (like shred does to files), and where the system is persistent even though any particular table likely won't be (so can't just shred the disks at "completion"), I'm trying to figure out my options for securely deleting the underlying data files when a table is dropped.
>>>
>>> As background, I'm not a DBA, but I am an experienced implementor in many languages, contexts, and databases. I've looked online and haven't been able to find a way to ask PostgreSQL to do the equivalent of shredding its underlying files before releasing them to the OS when a table is DROPped. Is there a built-in way to ask PostgreSQL to do this? (I might just not have searched for the right thing - my apologies if I missed something)
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>>> A partial answer we're looking at is shredding the underlying data files for a given relation and its indexes manually before dropping the tables, but this isn't so elegant, and I'm not sure it is getting all the information from the tables that we need to delete.
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>>> We also are looking at strategies for shredding free space on our data disk - either running a utility to do that, or periodically replicating the data volume, swapping in the results of the copy, then shredding the entire volume that was the source so its "free" space is securely overwritten in the process.
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>>> Are we missing something? Are there other options we haven't found? If we have to clean up manually, are there other places we need to go to shred data than the relation files for a given table, and all its related indexes, in the database's folder? Any help or advice will be greatly appreciated.
>> I'd write a program that fills all free space on disk with a specific pattern. You're probably using a logging filesystem, so that'll be far from perfect, though.
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>> --
>> Angular momentum makes the world go 'round.
>>

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Angular momentum makes the world go 'round.