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mdbx: корректировка README.

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Леонид Юрьев (Leonid Yuriev) 2024-09-10 08:41:23 +03:00
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@ -220,7 +220,8 @@ Thus syncing data to disk might be a bottleneck for write intensive workload.
but read transactions prevents recycling an old retired/freed pages, since it read ones. Thus altering of data during a parallel
long-lived read operation will increase the process work set, may exhaust entire free database space,
the database can grow quickly, and result in performance degradation.
Try to avoid long running read transactions.
Try to avoid long running read transactions, otherwise use [transaction parking](https://libmdbx.dqdkfa.ru/group__c__transactions.html#ga2c2c97730ff35cadcedfbd891ac9b12f)
and/or [Handle-Slow-Readers callback](https://libmdbx.dqdkfa.ru/group__c__err.html#ga2cb11b56414c282fe06dd942ae6cade6).
5. _libmdbx_ is extraordinarily fast and provides minimal overhead for data access,
so you should reconsider using brute force techniques and double check your code.
@ -278,45 +279,43 @@ the user's point of view.
5. The same database format for 32- and 64-bit builds.
> _libmdbx_ database format depends only on the [endianness](https://en.wikipedia.org/wiki/Endianness) but not on the [bitness](https://en.wiktionary.org/wiki/bitness).
6. LIFO policy for Garbage Collection recycling. This can significantly increase write performance due write-back disk cache up to several times in a best case scenario.
6. The "Big Foot" feature than solves speific performance issues with huge transactions and extra-large page-number-lists.
7. LIFO policy for Garbage Collection recycling. This can significantly increase write performance due write-back disk cache up to several times in a best case scenario.
> LIFO means that for reuse will be taken the latest becomes unused pages.
> Therefore the loop of database pages circulation becomes as short as possible.
> In other words, the set of pages, that are (over)written in memory and on disk during a series of write transactions, will be as small as possible.
> Thus creates ideal conditions for the battery-backed or flash-backed disk cache efficiency.
7. Fast estimation of range query result volume, i.e. how many items can
8. Parking of read transactions with ousting and auto-restart, [Handle-Slow-Readers callback](https://libmdbx.dqdkfa.ru/group__c__err.html#ga2cb11b56414c282fe06dd942ae6cade6) to resolve an issues due to long-lived read transactions.
9. Fast estimation of range query result volume, i.e. how many items can
be found between a `KEY1` and a `KEY2`. This is a prerequisite for build
and/or optimize query execution plans.
> _libmdbx_ performs a rough estimate based on common B-tree pages of the paths from root to corresponding keys.
8. Database integrity check API both with standalone `mdbx_chk` utility.
10. Database integrity check API both with standalone `mdbx_chk` utility.
9. Support for opening databases in the exclusive mode, including on a network share.
10. Zero-length for keys and values.
11. Ability to determine whether the particular data is on a dirty page
or not, that allows to avoid copy-out before updates.
11. Support for opening databases in the exclusive mode, including on a network share.
12. Extended information of whole-database, tables/sub-databases, transactions, readers enumeration.
> _libmdbx_ provides a lot of information, including dirty and leftover pages
> for a write transaction, reading lag and holdover space for read transactions.
13. Extended update and delete operations.
> _libmdbx_ allows one _at once_ with getting previous value
> and addressing the particular item from multi-value with the same key.
13. Support of Zero-length for keys and values.
14. Useful runtime options for tuning engine to application's requirements and use cases specific.
15. Automated steady sync-to-disk upon several thresholds and/or timeout via cheap polling.
16. Sequence generation and three persistent 64-bit markers.
16. Ability to determine whether the particular data is on a dirty page
or not, that allows to avoid copy-out before updates.
17. Handle-Slow-Readers callback to resolve a database full/overflow issues due to long-lived read transaction(s).
18. Ability to determine whether the cursor is pointed to a key-value
pair, to the first, to the last, or not set to anything.
17. Extended update and delete operations.
> _libmdbx_ allows one _at once_ with getting previous value
> and addressing the particular item from multi-value with the same key.
18. Sequence generation and three persistent 64-bit vector-clock like markers.
## Other fixes and specifics