ESQL: Split large pages on load sometimes (#131053) #132033
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This adds support for splitting `Page`s of large values when loading from single segment, non-descending hits. This is hottest code path as it's how we load data for aggregation. So! We had to make very very very sure this doesn't slow down the fast path of loading doc values. Caveat - this only defends against loading large values via the row-by-row load mechanism that we use for stored fields and _source. That covers the most common kinds of large values - mostly `text` and geo fields. If we need to split further on docs values, we'll have to invent something for them specifically. For now, just row-by-row. This works by flipping the order in which we load row-by-row and column-at-a-time values. Previously we loaded all column-at-a-time values first because that was simpler. Then we loaded all of the row-by-row values. Now we save the column-at-a-time values and instead load row-by-row until the `Page`'s estimated size is larger than a "jumbo" size which defaults to a megabyte. Once we load enough rows that we estimate the page is "jumbo", we then stop loading rows. The Page will look like this: ``` | txt1 | int | txt2 | long | double | |------|-----|------|------|--------| | XXXX | | XXXX | | | | XXXX | | XXXX | | | | XXXX | | XXXX | | | | XXXX | | XXXX | | | | XXXX | | XXXX | | | | XXXX | | XXXX | | | <-- after loading this row | | | | | | we crossed to "jumbo" size | | | | | | | | | | | | | | | | | | <-- these rows are entirely empty | | | | | | | | | | | | ``` Then we chop the page to the last row: ``` | txt1 | int | txt2 | long | double | |------|-----|------|------|--------| | XXXX | | XXXX | | | | XXXX | | XXXX | | | | XXXX | | XXXX | | | | XXXX | | XXXX | | | | XXXX | | XXXX | | | | XXXX | | XXXX | | | ``` Then fill in the column-at-a-time columns: ``` | txt1 | int | txt2 | long | double | |------|-----|------|------|--------| | XXXX | 1 | XXXX | 11 | 1.0 | | XXXX | 2 | XXXX | 22 | -2.0 | | XXXX | 3 | XXXX | 33 | 1e9 | | XXXX | 4 | XXXX | 44 | 913 | | XXXX | 5 | XXXX | 55 | 0.1234 | | XXXX | 6 | XXXX | 66 | 3.1415 | ``` And then we return *that* `Page`. On the next `Driver` iteration we start from where we left off.
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This adds support for splitting
Pages of large values when loading from single segment, non-descending hits. This is hottest code path as it's how we load data for aggregation. So! We had to make very very very sure this doesn't slow down the fast path of loading doc values.Caveat - this only defends against loading large values via the row-by-row load mechanism that we use for stored fields and _source. That covers the most common kinds of large values - mostly
textand geo fields. If we need to split further on docs values, we'll have to invent something for them specifically. For now, just row-by-row.This works by flipping the order in which we load row-by-row and column-at-a-time values. Previously we loaded all column-at-a-time values first because that was simpler. Then we loaded all of the row-by-row values. Now we save the column-at-a-time values and instead load row-by-row until the
Page's estimated size is larger than a "jumbo" size which defaults to a megabyte.Once we load enough rows that we estimate the page is "jumbo", we then stop loading rows. The Page will look like this:
Then we chop the page to the last row:
Then fill in the column-at-a-time columns:
And then we return that
Page. On the nextDriveriteration we start from where we left off.