PostgreSQL – Vacuum Basics

To implement one of the ACID properties called “Isolation”, PostgreSQL provides MVCC (Multi-Version Concurrency Control). In this way, the maximum possible concurrency among current transactions is achievable. PostgreSQL does this by creating versions of each tuple when the tuple receives any modifications. For instance, say that a tuple received n concurrent modifications. The n versions of the same tuple will still be kept and will make the last committed modified tuple visible to other transactions. Now, this will lead to more disk space usage because you are having both visible and non-visible tuples. The good news is that PostgreSQL offers a few ways to reuse the non-visible tuples to make way for further write operations. Read More

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