ADBDEV-5541: Backup statistics by one row

[RekGRpth]

Backup statistics by one row

gpbackup backuped statistics, loading them entirely into RAM. This can create
difficulties in the case of a huge number of tables and may come down to OOM.

This patch changes the backup logic: now statistics are not loaded entirely at
once, but are requested in portions by one row. This significantly reduces RAM
consumption when backing up statistics.

The test was not added because the result does not change. And to watch the
difference in memory consumption, we need a lot of tables with large statistics,
which is not very good for running tests.

[whitehawk]

When reading the description:

...
gpbackup backups statistics, first loading them entirely into RAM.
...
This patch allows to backup statistics not entirely at once, but by requesting them in portions by one row.
...

I can interpret in a way that this change adds an option: either use old way (load everything into RAM) or new way (get the data in portions).

I think it is better to tune the description, for ex:

...
gpbackup backuped statistics, loading them entirely into RAM.
...
This patch changes the backup logic: now statistics are not loaded entirely at once, but are requested in portions by one row.
...

to avoid possible wrong interpetation.

[RekGRpth]

When reading the description:

...
gpbackup backups statistics, first loading them entirely into RAM.
...
This patch allows to backup statistics not entirely at once, but by requesting them in portions by one row.
...

I can interpret in a way that this change adds an option: either use old way (load everything into RAM) or new way (get the data in portions).

I think it is better to tune the description, for ex:

...
gpbackup backuped statistics, loading them entirely into RAM.
...
This patch changes the backup logic: now statistics are not loaded entirely at once, but are requested in portions by one row.
...

to avoid possible wrong interpetation.

applied

[whitehawk]

In the description:

gpbackup backups statistics, first them entirely into RAM.

I guess the 'loading' word is missed. Also, it is better to use past tense for old problematic behavior.

[RekGRpth]

In the description:

gpbackup backups statistics, first them entirely into RAM.

I guess the 'loading' word is missed. Also, it is better to use past tense for old problematic behavior.

fixed