used in*time series* (for example trade date). Presence of such column in projection allows to incrementally update projection.

Generated`PNAME_refresh()` method calls`populate` method with correspondent values of`predicate` and

`sort` parameters, selecting from original table only rows with`order_by` column value greater than maximal

value of this column in projection. It assumes that`order_by` is unique or at least refresh is done at the moment when there is some gap

value of this column intheprojection. It assumes that`order_by` is unique or at least refresh is done at the moment when there is some gap

in collected events. In addition to`order_by`, sort list for`populate` includes all scalar (grouping) columns.

It allows to efficiently group imported data by scalar columns and fill VOPS tiles (vector columns) with data.

When`order_by` attribute is specified, VOPS creates two functional BRIN indexes on`first()` and`last()`

functions of this attribute. Presence of such indexes allows to efficiently select time slices. If original query contains

predicates like`(trade_date between '01-01-2017' and '01-01-2018')` then VOPS projection substitution mechanism adds

`(first(trade_date) >= '01-01-2017' and last(trade_date) >= '01-01-2018')` conjuncts whichallows Postgres optimizer to use BRIN

indexes to locate affected pages.

predicate like`(trade_date between '01-01-2017' and '01-01-2018')` then VOPS projection substitution mechanism adds

`(first(trade_date) >= '01-01-2017' and last(trade_date) >= '01-01-2018')` conjuncts whichallow Postgres optimizer to use BRIN

index to locate affected pages.

In in addition to BRIN indexes for`order_by` attribute, VOPS also creates BRIN index for grouping (scalar) columns.

Such index allows to efficiently select groups and perform index join.

1. Query doesn't contain joins.

2. Query performs aggregation of vector (tile) columns.

3. All other expressions in target list,`ORDER BY` /`GROUP BY` clausesrefers only to scalar attributes of projection.

3. All other expressions in target list,`ORDER BY` /`GROUP BY` clausesrefer only to scalar attributes of projection.

Projection can be removed using`drop_projection(projection_name text)` function.

It not only drops the correspondent table, but also removes information about it from`vops_partitions` table