diff --git a/doc/TODO b/doc/TODO index 7c88a4afe33216459eb3ff1267a93f30b5e8bee7..29477a21a72f0d1e6507b3b8e5805df34e992f4b 100644 --- a/doc/TODO +++ b/doc/TODO @@ -2,7 +2,7 @@ PostgreSQL TODO List ==================== Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us) -Last updated: Thu Sep 1 20:49:44 EDT 2005 +Last updated: Fri Sep 2 11:22:36 EDT 2005 The most recent version of this document can be viewed at http://www.postgresql.org/docs/faqs.TODO.html. @@ -962,6 +962,26 @@ Miscellaneous Performance could hit disk before WAL is written. * Add a script to ask system configuration questions and tune postgresql.conf +* 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. + * Use a phantom command counter for nested subtransactions to reduce per-tuple overhead * Research storing disk pages with no alignment/padding diff --git a/doc/src/FAQ/TODO.html b/doc/src/FAQ/TODO.html index f24c9a5605f6f3899783cbcc6757c914c653c7cf..d3cb00608933485de0f640b682b9cd5200045ce1 100644 --- a/doc/src/FAQ/TODO.html +++ b/doc/src/FAQ/TODO.html @@ -8,7 +8,7 @@ <body bgcolor="#FFFFFF" text="#000000" link="#FF0000" vlink="#A00000" alink="#0000FF"> <h1><a name="section_1">PostgreSQL TODO List</a></h1> <p>Current maintainer: Bruce Momjian (<a href="mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</a>)<br/> -Last updated: Thu Sep 1 20:49:44 EDT 2005 +Last updated: Fri Sep 2 11:22:36 EDT 2005 </p> <p>The most recent version of this document can be viewed at<br/> <a href="http://www.postgresql.org/docs/faqs.TODO.html">http://www.postgresql.org/docs/faqs.TODO.html</a>. @@ -867,6 +867,25 @@ first. could hit disk before WAL is written. </p> </li><li>Add a script to ask system configuration questions and tune postgresql.conf + </li><li>Merge xmin/xmax/cmin/cmax back into three header fields +<p> 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. +</p> +<p> One possible solution is to create a phantom cid which represents a + cmin/cmax pair and is stored in local memory. +</p> </li><li>Use a phantom command counter for nested subtransactions to reduce per-tuple overhead </li><li>Research storing disk pages with no alignment/padding