Enhance the wal2 header comment in wal.c to explain how the wal-hook is

invoked in wal2 mode.

FossilOrigin-Name: 118aa7e32a94ad971a955ab60db5bfc5b6241f93734a41ba83ab72ea71bc9aaa

diff --git a/manifest b/manifest
index 6011543e8e0b32c0756ec704d07ecf0f4fa637c5..4a2e015de63cd3e01b60407127533f37073368b5 100644 (file)
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Add\sextra\stest\scase\sto\swal2recover.test.
-D 2018-12-17T15:22:24.652
+C Enhance\sthe\swal2\sheader\scomment\sin\swal.c\sto\sexplain\show\sthe\swal-hook\sis\ninvoked\sin\swal2\smode.
+D 2018-12-22T15:50:00.221
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in 68d0ba0f0b533d5bc84c78c13a6ce84ee81183a67014caa47a969e67f028fa1c
@@ -590,7 +590,7 @@ F src/vdbesort.c 90aad5a92608f2dd771c96749beabdb562c9d881131a860a7a5bccf66dc3be7
 F src/vdbetrace.c 79d6dbbc479267b255a7de8080eee6e729928a0ef93ed9b0bfa5618875b48392
 F src/vtab.c 70188a745dc4e57d26e942681ff4b2912b7c8249ad5de3f60f0677b4337bcfaa
 F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
-F src/wal.c beca1487f7cecd1d6a965ba899a5a6b8868b3eb80580d33b2a73f8e37ab4901b
+F src/wal.c 93dc58d21bc6e1d08edfa42ba03e07f9652cd4c17c4205c20528e84e3b26c892
 F src/wal.h d2a69695c84137f76e19a247a342cb02ab0131001b6f58153d94b71195bbd84d
 F src/walker.c fb94aadc9099ff9c6506d0a8b88d51266005bcaa265403f3d7caf732a562eb66
 F src/where.c 3818e8a736a05d2cb194e64399af707e367fbcc5c251d785804d02eaf121288e
@@ -1792,7 +1792,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 9cb5f8dab685f5ea36ad142cfa588dee82e87f3a89e8dcf84e0ee124bb29bc7f
-R 126e20a307613344c2c21be5333f4cc9
+P 1a5aa73435b11fff0567672dc921d34aad57adf0381ad430e1389f39a6f025b7
+R ae7a76a21801add0bf32d05f9dbcc082
 U dan
-Z 0b7e3c508818c5bb27b7cd0635e26287
+Z e66e7dac085eccd9e1ba0c66084130c4

diff --git a/manifest.uuid b/manifest.uuid
index 61b581122e4381d94829a4dd97a092c318ecb061..d16063f1f26ec25b0893e2fad81a3d7b163ce329 100644 (file)
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-1a5aa73435b11fff0567672dc921d34aad57adf0381ad430e1389f39a6f025b7
\ No newline at end of file
+118aa7e32a94ad971a955ab60db5bfc5b6241f93734a41ba83ab72ea71bc9aaa
\ No newline at end of file

diff --git a/src/wal.c b/src/wal.c
index 6200d59c9a749b25c5a944d3f2468437ce9e988d..3e9b32525bba396ffd9ce7334f777ab65b7b53d3 100644 (file)
--- a/src/wal.c
+++ b/src/wal.c
@@ -306,6 +306,31 @@
 ** The first wal file takes the same name as the wal file in legacy wal
 ** mode systems - "<db>-wal". The second is named "<db>-wal2".
 **
+** CHECKPOINTS
+**
+** The "pre-configured size" mentioned above is the value set by 
+** "PRAGMA journal_size_limit". Or, if journal_size_limit is not set, 
+** 1000 pages.
+**
+** There is only a single type of checkpoint in wal2 mode (no "truncate",
+** "restart" etc.), and it always checkpoints the entire contents of a single
+** wal file. A wal file cannot be checkpointed until after a writer has written
+** the first transaction into the other wal file and all readers are reading a
+** snapshot that includes at least one transaction from the other wal file.
+**
+** The wal-hook, if one is registered, is invoked after a write-transaction
+** is committed, just as it is in legacy wal mode. The integer parameter
+** passed to the wal-hook is the total number of uncheckpointed frames in both
+** wal files. Except, the parameter is set to zero if there is no frames 
+** that may be checkpointed. This happens in two scenarios:
+**
+**   1. The "other" wal file (the one that the writer did not just append to)
+**      is completely empty, or
+**
+**   2. The "other" wal file (the one that the writer did not just append to)
+**      has already been checkpointed.
+**
+**
 ** WAL FILE FORMAT
 **
 ** The file format used for each wal file in wal2 mode is the same as for