PostgreSQL

Postgres vs. Oracle access paths IX – Tid Scan

By Franck Pachot . In the previous post we have seen how Postgres and Oracle finds the table row from the index entry. It uses the TID / ROWID. I’ll focus on this access path(…)

Postgres vs. Oracle access paths VIII – Index Scan and Filter

By Franck Pachot . In the previous post we have seen a nice optimization to lower the consequences of bad correlation between the index and the table physical order: a bitmap, which may include false positives(…)

Postgres vs. Oracle access paths VI – Index Scan

By Franck Pachot . In the previous post my queries were still reading the indexed column only, from a table which had no modifications since the last vacuum, and then didn't need to read table pages:(…)

Postgres vs. Oracle access paths V – FIRST ROWS and MIN/MAX

By Franck Pachot . We have seen how an index can help to avoid a sorting operation in the previous post. This avoids a blocking operation: the startup cost is minimal and the first rows can(…)

Postgres vs. Oracle access paths IV – Order By and Index

By Franck Pachot . I realize that I'm talking about indexes in Oracle and Postgres, and didn't mention yet the best website you can find about indexes, with concepts and examples for all RDBMS: http://use-the-index-luke.com. You(…)

Postgres vs. Oracle access paths III – Partial Index

By Franck Pachot . In the previous post I said that an Index Only Access needs to find all rows in the index. Here is a case where, with similar data, Postgres can find all rows(…)

Postgres vs. Oracle access paths II – Index Only Scan

By Franck Pachot . In the previous post I've explained a sequential scan by accident: my query needed only one column which was indexed, and I expected to read the index rather than the table. And(…)

Postgres vs. Oracle access paths I – Seq Scan

By Franck Pachot . Here is the first test I've done for my Postgres vs. Oracle access paths series and the first query did a sequential scan. It illustrates the first constant you find in the(…)

Postgres unique constraint

By Franck Pachot . I'll start a series on Postgres vs. Oracle access paths because I know Oracle and I learn Postgres. While preparing it, I came upon some surprises because I'm so used to Oracle(…)

Postgres vs. Oracle access paths – intro

By Franck Pachot . This is the start of a series on PostgreSQL execution plans, access path, join methods, hints and execution statistics. The approach will compare Postgres and Oracle. It is not a comparison to see which one is(…)