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mdbx: updates the README to be less ugly.

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Change-Id: I41835f184cf9cc8ea1db0337e01449150b0b185f
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Leonid Yuriev 2019-07-18 20:19:44 +03:00
parent 6413dcc2c6
commit 7b4f5d9c4b
1 changed files with 26 additions and 29 deletions
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README.md
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@ -187,15 +187,14 @@ optimal query execution plan.
5. `mdbx_chk` tool for DB integrity check. 5. `mdbx_chk` tool for DB integrity check.
6. Support for keys and values of zero length, including sorted 6. Support for keys and values of zero length, including multi-values (aka sorted duplicates).
duplicates.
7. Ability to assign up to 3 persistent 64-bit markers to commiting transaction with 7. Ability to assign up to 3 persistent 64-bit markers to commiting transaction with
`mdbx_canary_put()` and then get them in read transaction by `mdbx_canary_put()` and then get them in read transaction by
`mdbx_canary_get()`. `mdbx_canary_get()`.
8. Ability to update or delete record and get previous value via 8. Ability to update or delete record and get previous value via `mdbx_replace()`.
`mdbx_replace()`. Also can update specific multi-value. Also allows update the specific item from multi-value with the same key.
9. Sequence generation via `mdbx_dbi_sequence()`. 9. Sequence generation via `mdbx_dbi_sequence()`.
@ -217,30 +216,29 @@ duplicates.
* abort current write transaction with returning error code. * abort current write transaction with returning error code.
11. Ability to open DB in exclusive mode with `MDBX_EXCLUSIVE` flag. 11. Ability to open DB in exclusive mode by `MDBX_EXCLUSIVE` flag.
12. Ability to get how far current read-only snapshot is from latest 12. Ability to get how far current read-transaction snapshot lags
version of the DB by `mdbx_txn_straggler()`. from the latest version of the DB by `mdbx_txn_straggler()`.
13. Ability to explicitly request update of present record without 13. Ability to explicitly update the existing record, not insertion
creating new record. Implemented as `MDBX_CURRENT` flag for a new one. Implemented as `MDBX_CURRENT` flag for `mdbx_put()`.
`mdbx_put()`.
14. Fixed `mdbx_cursor_count()`, which returns correct count of 14. Fixed `mdbx_cursor_count()`, which returns correct count of
duplicated for all table types and any cursor position. duplicated (aka multi-value) for all cases and any cursor position.
15. `mdbx_env_info()` to getting additional info, including number of 15. `mdbx_env_info()` to getting additional info, including number of
the oldest snapshot of DB, which is used by one of the readers. the oldest snapshot of DB, which is used by someone of the readers.
16. `mdbx_del()` doesn't ignore additional argument (specifier) `data` 16. `mdbx_del()` doesn't ignore additional argument (specifier) `data`
for tables without duplicates (without flag `MDBX_DUPSORT`), if `data` for tables without duplicates (without flag `MDBX_DUPSORT`), if `data`
is not null then always uses it to verify record, which is being is not null then always uses it to verify record, which is being
deleted. deleted.
17. Ability to open dbi-table with simultaneous setup of comparators for 17. Ability to open dbi-table with simultaneous with race-free setup
keys and values, via `mdbx_dbi_open_ex()`. of comparators for keys and values, via `mdbx_dbi_open_ex()`.
18. `mdbx_is_dirty()`to find out if key or value is on dirty page, that 18. `mdbx_is_dirty()`to find out if given key or value is on dirty page, that
useful to avoid copy-out before updates. useful to avoid copy-out before updates.
19. Correct update of current record in `MDBX_CURRENT` mode of 19. Correct update of current record in `MDBX_CURRENT` mode of
@ -255,21 +253,21 @@ useful to avoid copy-out before updates.
22. Ability to get value by key and duplicates count by `mdbx_get_ex()`. 22. Ability to get value by key and duplicates count by `mdbx_get_ex()`.
23. Functions `mdbx_cursor_on_first()` and `mdbx_cursor_on_last()`, 23. Functions `mdbx_cursor_on_first()` and `mdbx_cursor_on_last()`,
which allows to know if cursor is currently on first or last position which allows to check cursor is currently on first or last position
respectively. respectively.
24. Automatic creation of synchronization points (flush changes to 24. Automatic creation of steady commit-points (flushing data to the
persistent storage) when changes reach set threshold (threshold can be disk) when the volume of changes reaches a threshold, which can be
set by `mdbx_env_set_syncbytes()`). set by `mdbx_env_set_syncbytes()`.
25. Control over debugging and receiving of debugging messages via 25. Control over debugging and receiving of debugging messages via
`mdbx_setup_debug()`. `mdbx_setup_debug()`.
26. Function `mdbx_env_pgwalk()` for page-walking all pages in DB. 26. Function `mdbx_env_pgwalk()` for page-walking the DB.
27. Three meta-pages instead of two, this allows to guarantee 27. Three meta-pages instead of two, that allows to guarantee
consistently update weak sync-points without risking to corrupt last consistency of data when updating weak commit-points without the
steady sync-point. risk of damaging the last steady commit-point.
28. Guarantee of DB integrity in `WRITEMAP+MAPSYNC` mode: 28. Guarantee of DB integrity in `WRITEMAP+MAPSYNC` mode:
> Current _libmdbx_ gives a choice of safe async-write mode (default) > Current _libmdbx_ gives a choice of safe async-write mode (default)
@ -281,9 +279,9 @@ steady sync-point.
creation of steady synchronization point) via `mdbx_env_close_ex()`. creation of steady synchronization point) via `mdbx_env_close_ex()`.
30. If read transaction is aborted via `mdbx_txn_abort()` or 30. If read transaction is aborted via `mdbx_txn_abort()` or
`mdbx_txn_reset()` then DBI-handles, which were opened in it, aren't `mdbx_txn_reset()` then DBI-handles, which were opened during it,
closed or deleted. This allows to avoid several types of hard-to-debug will not be closed or deleted. In several cases this allows
errors. to avoid hard-to-debug errors.
31. All cursors in all read and write transactions can be reused by 31. All cursors in all read and write transactions can be reused by
`mdbx_cursor_renew()` and MUST be freed explicitly. `mdbx_cursor_renew()` and MUST be freed explicitly.
@ -300,9 +298,8 @@ errors.
## Gotchas ## Gotchas
1. At one moment there can be only one writer. But this allows to 1. There cannot be more than one writer at a time. This allows serialize an
serialize writes and eliminate any possibility of conflict or logical updates and eliminate any possibility of conflicts, deadlocks or logical errors.
errors during transaction rollback.
2. No [WAL](https://en.wikipedia.org/wiki/Write-ahead_logging) means 2. No [WAL](https://en.wikipedia.org/wiki/Write-ahead_logging) means
relatively big [WAF](https://en.wikipedia.org/wiki/Write_amplification) relatively big [WAF](https://en.wikipedia.org/wiki/Write_amplification)