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mdbx: add notes about range query estimation into READMEs.

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Change-Id: Ia9e0b7e393082115839483ea7a3b37fb37ba0308
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Leonid Yuriev
2019-03-06 00:40:53 +03:00
parent ee899a21ed
commit 7f8cd66e11
2 changed files with 93 additions and 84 deletions
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README.md
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@@ -170,30 +170,18 @@ regular maintenance. Backups can be made on the fly on working DB
Improvements over LMDB
======================
1. `mdbx_chk` tool for DB integrity check.
2. Automatic dynamic DB size management according to the parameters
specified by `mdbx_env_set_geometry()` function. Including including
1. Automatic dynamic DB size management according to the parameters
specified by `mdbx_env_set_geometry()` function. Including
growth step and truncation threshold, as well as the choice of page
size.
3. Automatic returning of freed pages into unallocated space at the end
of database file with optionally automatic shrinking it. This reduces
2. Automatic returning of freed pages into unallocated space at the end
of database file, with optionally automatic shrinking it. This reduces
amount of pages resides in RAM and circulated in disk I/O. In fact
_libmdbx_ constantly performs DB compactification, without spending
additional resources for that.
4. Support for keys and values of zero length, including sorted
duplicates.
5. Ability to assign up to 3 markers to commiting transaction with
`mdbx_canary_put()` and then get them in read transaction by
`mdbx_canary_get()`.
6. Ability to update or delete record and get previous value via
`mdbx_replace()` Also can update specific multi-value.
7. `LIFO RECLAIM` mode:
3. `LIFO RECLAIM` mode:
The newest pages are picked for reuse instead of the oldest. This allows
to minimize reclaim loop and make it execution time independent of total
@@ -204,9 +192,25 @@ duplicates.
[BBWC](https://en.wikipedia.org/wiki/Disk_buffer#Write_acceleration)
this may greatly improve write performance.
8. Sequence generation via `mdbx_dbi_sequence()`.
4. Fast estimation of range query result size via functions `mdbx_estimate_range()`,
`mdbx_estimate_move()` and `mdbx_estimate_distance()`. E.g. for selection the
optimal query execution plan.
9. `OOM-KICK` callback.
5. `mdbx_chk` tool for DB integrity check.
6. Support for keys and values of zero length, including sorted
duplicates.
7. Ability to assign up to 3 markers to commiting transaction with
`mdbx_canary_put()` and then get them in read transaction by
`mdbx_canary_get()`.
8. Ability to update or delete record and get previous value via
`mdbx_replace()`. Also can update specific multi-value.
9. Sequence generation via `mdbx_dbi_sequence()`.
10. `OOM-KICK` callback.
`mdbx_env_set_oomfunc()` allows to set a callback, which will be called
in the event of DB space exhausting during long-time read transaction in
@@ -224,75 +228,75 @@ duplicates.
* abort current write transaction with returning error code.
10. Ability to open DB in exclusive mode with `MDBX_EXCLUSIVE` flag.
11. Ability to open DB in exclusive mode with `MDBX_EXCLUSIVE` flag.
11. Ability to get how far current read-only snapshot is from latest
12. Ability to get how far current read-only snapshot is from latest
version of the DB by `mdbx_txn_straggler()`.
12. Ability to explicitly request update of present record without
13. Ability to explicitly request update of present record without
creating new record. Implemented as `MDBX_CURRENT` flag for
`mdbx_put()`.
13. 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.
14. `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.
15. `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`
is not null then always uses it to verify record, which is being
deleted.
16. Ability to open dbi-table with simultaneous setup of comparators for
17. Ability to open dbi-table with simultaneous setup of comparators for
keys and values, via `mdbx_dbi_open_ex()`.
17. `mdbx_is_dirty()`to find out if key or value is on dirty page, that
18. `mdbx_is_dirty()`to find out if key or value is on dirty page, that
useful to avoid copy-out before updates.
18. Correct update of current record in `MDBX_CURRENT` mode of
19. Correct update of current record in `MDBX_CURRENT` mode of
`mdbx_cursor_put()`, including sorted duplicated.
19. Check if there is a row with data after current cursor position via
20. Check if there is a row with data after current cursor position via
`mdbx_cursor_eof()`.
20. Additional error code `MDBX_EMULTIVAL`, which is returned by
21. Additional error code `MDBX_EMULTIVAL`, which is returned by
`mdbx_put()` and `mdbx_replace()` in case is ambiguous update or delete.
21. 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()`.
22. 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
respectively.
23. Automatic creation of synchronization points (flush changes to
24. Automatic creation of synchronization points (flush changes to
persistent storage) when changes reach set threshold (threshold can be
set by `mdbx_env_set_syncbytes()`).
24. Control over debugging and receiving of debugging messages via
25. Control over debugging and receiving of debugging messages via
`mdbx_setup_debug()`.
25. Function `mdbx_env_pgwalk()` for page-walking all pages in DB.
26. Function `mdbx_env_pgwalk()` for page-walking all pages in DB.
26. Three meta-pages instead of two, this allows to guarantee
27. Three meta-pages instead of two, this allows to guarantee
consistently update weak sync-points without risking to corrupt last
steady sync-point.
27. 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)
> and `UTTERLY_NOSYNC` mode which may result in full
> DB corruption during system crash as with LMDB. For details see
> [Data safety in async-write mode](#data-safety-in-async-write-mode).
28. Ability to close DB in "dirty" state (without data flush and
29. Ability to close DB in "dirty" state (without data flush and
creation of steady synchronization point) via `mdbx_env_close_ex()`.
29. 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
closed or deleted. This allows to avoid several types of hard-to-debug
errors.
30. 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.
> ## Caution, please pay attention!
>
@@ -594,11 +598,11 @@ $ objdump -f -h -j .text libmdbx.so
libmdbx.so: file format elf64-x86-64
architecture: i386:x86-64, flags 0x00000150:
HAS_SYMS, DYNAMIC, D_PAGED
start address 0x000030e0
start address 0x0000000000003870
Sections:
Idx Name Size VMA LMA File off Algn
11 .text 00014d84 00000000000030e0 00000000000030e0 000030e0 2**4
11 .text 000173d4 0000000000003870 0000000000003870 00003870 2**4
CONTENTS, ALLOC, LOAD, READONLY, CODE
```