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* Merge xmin/xmax/cmin/cmax back into three header fields Before subtransactions, there used to be only three fields needed to store these four values. This was possible because only the current transaction looks at the cmin/cmax values. If the current transaction created and expired the row the fields stored where xmin (same as xmax), cmin, cmax, and if the transaction was expiring a row from a another transaction, the fields stored were xmin (cmin was not needed), xmax, and cmax. Such a system worked because a transaction could only see committed rows from another transaction. However, subtransactions can see rows from outer transactions, and once the subtransaction completes, the outer transaction continues, requiring the storage of all four fields. With subtransactions, an outer transaction can create a row, a subtransaction expire it, and when the subtransaction completes, the outer transaction still has to have proper visibility of the row, for example, for cursors. One possible solution is to create a phantom cid which represents a cmin/cmax pair and is stored in local memory. |
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The FAQ* files in this directory are the master versions, and the ../../FAQ* text files are created using lynx: lynx -force_html -dont_wrap_pre -dump -hiddenlinks=ignore -nolist FAQ* The TODO.html file in this directory is not the master, but ../../TODO is. The conversion is done using txt2html: txt2html -m -s 100 -p 100 --xhtml --titlefirst \ --body_deco ' bgcolor="#FFFFFF" text="#000000" link="#FF0000" vlink="#A00000" alink="#0000FF"' \ --caps_tag '' \ /pgtop/doc/TODO | sed 's;\[\([^]]*\)\];[<a href="http://momjian.postgresql.org/cgi-bin/pgtodo?\1">\1</a>];g' > /pgtop/doc/src/FAQ/TODO.html