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Commit44fe30f

Browse files
Add default_char_signedness field to ControlFileData.
The signedness of the 'char' type in C isimplementation-dependent. For instance, 'signed char' is used bydefault on x86 CPUs, while 'unsigned char' is used on aarchCPUs. Previously, we accidentally let C implementation signednessaffect persistent data. This led to inconsistent results whencomparing char data across different platforms.This commit introduces a new 'default_char_signedness' field inControlFileData to store the signedness of the 'char' type. While thischange does not encourage the use of 'char' without explicitlyspecifying its signedness, this field can be used as a hint to ensureconsistent behavior for pre-v18 data files that store data sorted bythe 'char' type on disk (e.g., GIN and GiST indexes), especially incross-platform replication scenarios.Newly created database clusters unconditionally set the default charsignedness to true. pg_upgrade (with an upcoming commit) changes thisflag for clusters if the source database cluster hassignedness=false. As a result, signedness=false setting will becomerare over time. If we had known about the problem during the lastdevelopment cycle that forced initdb (v8.3), we would have made allclusters signed or all clusters unsigned. Making pg_upgrade the onlysource of signedness=false will cause the population of databaseclusters to converge toward that retrospective ideal.Bump catalog version (for the catalog changes) and PG_CONTROL_VERSION(for the additions in ControlFileData).Reviewed-by: Noah Misch <noah@leadboat.com>Discussion:https://postgr.es/m/CB11ADBC-0C3F-4FE0-A678-666EE80CBB07%40amazon.com
1 parent901a1cf commit44fe30f

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8 files changed

+64
-7
lines changed

8 files changed

+64
-7
lines changed

‎doc/src/sgml/func.sgml

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@@ -27991,6 +27991,11 @@ acl | {postgres=arwdDxtm/postgres,foo=r/postgres}
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<entry><type>integer</type></entry>
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</row>
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<row>
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<entry><structfield>default_char_signedness</structfield></entry>
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<entry><type>boolean</type></entry>
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</row>
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</tbody>
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</tgroup>
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</table>

‎src/backend/access/transam/xlog.c

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Original file line numberDiff line numberDiff line change
@@ -4284,6 +4284,33 @@ WriteControlFile(void)
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ControlFile->float8ByVal=FLOAT8PASSBYVAL;
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4287+
/*
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* Initialize the default 'char' signedness.
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*
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* The signedness of the char type is implementation-defined. For instance
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* on x86 architecture CPUs, the char data type is typically treated as
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* signed by default, whereas on aarch architecture CPUs, it is typically
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* treated as unsigned by default. In v17 or earlier, we accidentally let
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* C implementation signedness affect persistent data. This led to
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* inconsistent results when comparing char data across different
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* platforms.
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*
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* This flag can be used as a hint to ensure consistent behavior for
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* pre-v18 data files that store data sorted by the 'char' type on disk,
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* especially in cross-platform replication scenarios.
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*
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* Newly created database clusters unconditionally set the default char
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* signedness to true. pg_upgrade changes this flag for clusters that were
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* initialized on signedness=false platforms. As a result,
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* signedness=false setting will become rare over time. If we had known
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* about this problem during the last development cycle that forced initdb
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* (v8.3), we would have made all clusters signed or all clusters
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* unsigned. Making pg_upgrade the only source of signedness=false will
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* cause the population of database clusters to converge toward that
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* retrospective ideal.
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*/
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ControlFile->default_char_signedness= true;
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/* Contents are protected with a CRC */
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INIT_CRC32C(ControlFile->crc);
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COMP_CRC32C(ControlFile->crc,
@@ -4612,6 +4639,19 @@ DataChecksumsEnabled(void)
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return (ControlFile->data_checksum_version>0);
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}
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/*
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* Return true if the cluster was initialized on a platform where the
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* default signedness of char is "signed". This function exists for code
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* that deals with pre-v18 data files that store data sorted by the 'char'
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* type on disk (e.g., GIN and GiST indexes). See the comments in
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* WriteControlFile() for details.
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*/
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bool
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GetDefaultCharSignedness(void)
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{
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returnControlFile->default_char_signedness;
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}
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/*
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* Returns a fake LSN for unlogged relations.
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*

‎src/backend/utils/misc/pg_controldata.c

Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -203,8 +203,8 @@ pg_control_recovery(PG_FUNCTION_ARGS)
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Datum
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pg_control_init(PG_FUNCTION_ARGS)
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{
206-
Datumvalues[11];
207-
boolnulls[11];
206+
Datumvalues[12];
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boolnulls[12];
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TupleDesctupdesc;
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HeapTuplehtup;
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ControlFileData*ControlFile;
@@ -254,6 +254,9 @@ pg_control_init(PG_FUNCTION_ARGS)
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values[10]=Int32GetDatum(ControlFile->data_checksum_version);
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nulls[10]= false;
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values[11]=BoolGetDatum(ControlFile->default_char_signedness);
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nulls[11]= false;
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htup=heap_form_tuple(tupdesc,values,nulls);
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PG_RETURN_DATUM(HeapTupleGetDatum(htup));

‎src/bin/pg_controldata/pg_controldata.c

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Original file line numberDiff line numberDiff line change
@@ -336,6 +336,8 @@ main(int argc, char *argv[])
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(ControlFile->float8ByVal ?_("by value") :_("by reference")));
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printf(_("Data page checksum version: %u\n"),
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ControlFile->data_checksum_version);
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printf(_("Default char data signedness: %s\n"),
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(ControlFile->default_char_signedness ?_("signed") :_("unsigned")));
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printf(_("Mock authentication nonce: %s\n"),
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mock_auth_nonce_str);
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return0;

‎src/include/access/xlog.h

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@@ -231,6 +231,7 @@ extern XLogRecPtr GetXLogWriteRecPtr(void);
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externuint64GetSystemIdentifier(void);
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externchar*GetMockAuthenticationNonce(void);
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externboolDataChecksumsEnabled(void);
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externboolGetDefaultCharSignedness(void);
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externXLogRecPtrGetFakeLSNForUnloggedRel(void);
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externSizeXLOGShmemSize(void);
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externvoidXLOGShmemInit(void);

‎src/include/catalog/catversion.h

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@@ -57,6 +57,6 @@
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*/
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/*yyyymmddN */
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#defineCATALOG_VERSION_NO202502211
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#defineCATALOG_VERSION_NO202502212
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#endif

‎src/include/catalog/pg_control.h

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@@ -22,7 +22,7 @@
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/* Version identifier for this pg_control format */
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#definePG_CONTROL_VERSION1700
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#definePG_CONTROL_VERSION1800
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/* Nonce key length, see below */
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#defineMOCK_AUTH_NONCE_LEN32
@@ -221,6 +221,12 @@ typedef struct ControlFileData
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/* Are data pages protected by checksums? Zero if no checksum version */
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uint32data_checksum_version;
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224+
/*
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* True if the default signedness of char is "signed" on a platform where
226+
* the cluster is initialized.
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*/
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booldefault_char_signedness;
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/*
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* Random nonce, used in authentication requests that need to proceed
226232
* based on values that are cluster-unique, like a SASL exchange that

‎src/include/catalog/pg_proc.dat

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Original file line numberDiff line numberDiff line change
@@ -12206,9 +12206,9 @@
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descr => 'pg_controldata init state information as a function',
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proname => 'pg_control_init', provolatile => 'v', prorettype => 'record',
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proargtypes => '',
12209-
proallargtypes => '{int4,int4,int4,int4,int4,int4,int4,int4,int4,bool,int4}',
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proargmodes => '{o,o,o,o,o,o,o,o,o,o,o}',
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proargnames => '{max_data_alignment,database_block_size,blocks_per_segment,wal_block_size,bytes_per_wal_segment,max_identifier_length,max_index_columns,max_toast_chunk_size,large_object_chunk_size,float8_pass_by_value,data_page_checksum_version}',
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proallargtypes => '{int4,int4,int4,int4,int4,int4,int4,int4,int4,bool,int4,bool}',
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proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o}',
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proargnames => '{max_data_alignment,database_block_size,blocks_per_segment,wal_block_size,bytes_per_wal_segment,max_identifier_length,max_index_columns,max_toast_chunk_size,large_object_chunk_size,float8_pass_by_value,data_page_checksum_version,default_char_signedness}',
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prosrc => 'pg_control_init' },
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# subscripting support for built-in types

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