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PostgreSQL Replication by Hans-Jürgen Schönig, Zoltan Böszörmenyi

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The internal structure of the XLOG

We will use the transaction log throughout this book, and to give you a deeper insight into how things work on a technical level, we have added this section dealing exclusively with the internal workings of the XLOG machinery. We will avoid going down to the C level as this would be ways beyond the scope of this book, but we will provide you with insights that are hopefully deep enough.

Understanding the XLOG records

Changes made to the XLOG are record-based. What does that mean? Let us assume you are adding a row to a table:

test=# INSERT INTO t_test VALUES (1, 'hans');
INSERT 0 1

In this example, we are inserting into a table containing two columns. For the sake of this example, we want to assume that both columns ...

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