Add v0.9.0 release notes.

doc/Changelog

@@ -1,4 +1,6 @@
 pgcenter (master) unstable; urgency=low
+
+pgcenter (0.9.0) unstable; urgency=low
   * record/report: add support for millisecond resolution
   * add support of pg_stat_wal WAL usage statistics (Postgres 14)
   * add support of pg_stat_database sessions statistics (Postgres 14)

doc/release-notes/v0.9.0.md

@@ -0,0 +1,104 @@
+## Release 0.9.0
+
+Release date: 2021-06-15
+
+This release contains new features and variety of fixes from 0.8.0.
+
+### Overview
+
+Pgcenter 0.8.0 contains new features and enhancements, including:
+- add session statistics from `pg_stat_database` (Postgres 14)
+- add WAL usage statistics from `pg_stat_wal` (Postgres 14)
+- add progress statistics about running COPY commands from `pg_stat_progress_copy` (Postgres 14)
+- add filesystem stats for `top` utility
+- extend statistics about tables sizes
+- add support for millisecond resolution for `record` and `report` utilities
+- add naming convention for columns names
+
+The above items and other changes are explained in more detail in the sections below.
+
+### New features
+
+1. Support of session statistics from [pg_stat_database](https://www.postgresql.org/docs/devel/monitoring-stats.html#MONITORING-PG-STAT-DATABASE-VIEW) view.
+
+Upcoming Postgres 14 has new session statistics available in `pg_stat_database` view. It includes information about how 
+much time were spent by sessions, and how many sessions were established and terminated due to various reasons.
+Pgcenter now provides databases statistics as separate views: general and sessions (like statements or progress statistics).
+For `top` utility a new shortcut has been introduced: `G` - it opens "database statistics" menu. Existing `g` shortcut now is
+working as switcher between databases statistics.
+
+In the picture below, an example of database sessions statistics.
+
+![](https://drive.google.com/uc?export=view&id=14dKVMOLSMatotNINCbO8-hVcox-pnWVR)
+
+2. Support of WAL usage statistics from [pg_stat_wal](https://www.postgresql.org/docs/devel/monitoring-stats.html#MONITORING-PG-STAT-WAL-VIEW) view.
+
+Upcoming Postgres 14 has new WAL usage statistics available in `pg_stat_wal`. This view contains a single-row about how much WAL
+is generated during server lifetime. Pgcenter now provides statistics based on `pg_stat_wal` in `top`, `record` and `report` tools.
+
+In the picture below, an example of WAL usage statistics.
+
+![](https://drive.google.com/uc?export=view&id=17Yxmq35fh7fmhy5dtYsHG4M7LHief2W-)
+
+3. Support of progress statistics about running COPY commands from [pg_stat_progress_copy](https://www.postgresql.org/docs/devel/progress-reporting.html#COPY-PROGRESS-REPORTING) view.
+
+Upcoming Postgres 14 has new "progress" statistics about running `COPY` in `pg_stat_progress_copy` view. This view is useful for
+tracking COPY commands which usually executed during import and export data (via `pg_dump` or `copy` utilities). Pgcenter now
+provides statistics based on `pg_stat_progress_copy` in `top`, `record` and `report` tools.
+
+In the picture below, an example of COPY progress statistics.
+
+![](https://drive.google.com/uc?export=view&id=1djbdidLR_0W1g4KSdc8maXkIjw0mbxLT)
+
+4. Add extra statistics about filesystems usage for `top` utility.
+
+`top` utility provides "extra" statistics (is not displayed by default), about block devices and network interfaces. New statistics
+about mounted filesystems is available now. There is information about total size of filesystem, used and free space and inodes.
+New shortcut has been added, `F` - toggles (on/off) displaying of filesystem usage stats.
+
+In the picture below, an example of screen with enabled filesystem statistics.
+
+![](https://drive.google.com/uc?export=view&id=1ORGBTNklCVidgsozLg6dExHGqalqul-F)
+
+5. Extend statistics about tables sizes.
+
+New values are added for tables sizes statistics: size of tables metadata (VM, FSM, init forks) and TOASTs. This gives more
+detailed overview of how disk space are utilized by particular table.
+
+In the picture below, an example of statistics with new values.
+
+![](https://drive.google.com/uc?export=view&id=1Nx5Dp4nahOuSqVeSX8ySU7IFyE7PKOVT)
+
+6. Support of millisecond resolution in `record` and `report` utilities.
+
+Earlier versions of `record` tool was designed to record statistics with 1 second (and higher) interval. Now it is possible
+to record statistics with millisecond resolution. This might be useful for recording statistics more frequently, especially
+during short-term periods (e.g. benchmarks). The `report` tool also supports sub-second resolution and prints this information
+when do report.
+
+7. Add naming convention for statistics columns names.
+
+Common naming rules are introduced for all column names. The goal is to make name of columns clear for the user. All column
+names have been reviewed and renamed if it was required. 
+
+### Fixes
+- fix crash of `top` utility when selecting an item "outside" of menus.
+
+- fix rare bug of `top` utility when program crashes on switching between stats views.
+
+- fix errors related to wrong query templating when displaying tables statistics.
+
+- fix issue when pg_stat_statements cannot be found due to installed on schema other than 'public'.
+
+- fix error occurred when `record` and `top` utilities attempts collecting stats which is not supported by Postgres.
+
+### Other
+- Show program version info in the help screen of `top` utility.
+
+- When install pgcenter from packages, use `/usr/bin` system path instead of `/usr/local/bin`.
+
+- Add `apk` package format when building packages on release.
+
+- Add support of `pg_stat_database.numbackends` field.
+
+- Remove `--rate` flag of `report` utility.